Commit Graph

86 Commits

Author SHA1 Message Date
Paul E. McKenney 5f0d5a3ae7 mm: Rename SLAB_DESTROY_BY_RCU to SLAB_TYPESAFE_BY_RCU
A group of Linux kernel hackers reported chasing a bug that resulted
from their assumption that SLAB_DESTROY_BY_RCU provided an existence
guarantee, that is, that no block from such a slab would be reallocated
during an RCU read-side critical section.  Of course, that is not the
case.  Instead, SLAB_DESTROY_BY_RCU only prevents freeing of an entire
slab of blocks.

However, there is a phrase for this, namely "type safety".  This commit
therefore renames SLAB_DESTROY_BY_RCU to SLAB_TYPESAFE_BY_RCU in order
to avoid future instances of this sort of confusion.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: <linux-mm@kvack.org>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
[ paulmck: Add comments mentioning the old name, as requested by Eric
  Dumazet, in order to help people familiar with the old name find
  the new one. ]
Acked-by: David Rientjes <rientjes@google.com>
2017-04-18 11:42:36 -07:00
Tejun Heo 01fb58bcba slab: remove synchronous synchronize_sched() from memcg cache deactivation path
With kmem cgroup support enabled, kmem_caches can be created and
destroyed frequently and a great number of near empty kmem_caches can
accumulate if there are a lot of transient cgroups and the system is not
under memory pressure.  When memory reclaim starts under such
conditions, it can lead to consecutive deactivation and destruction of
many kmem_caches, easily hundreds of thousands on moderately large
systems, exposing scalability issues in the current slab management
code.  This is one of the patches to address the issue.

slub uses synchronize_sched() to deactivate a memcg cache.
synchronize_sched() is an expensive and slow operation and doesn't scale
when a huge number of caches are destroyed back-to-back.  While there
used to be a simple batching mechanism, the batching was too restricted
to be helpful.

This patch implements slab_deactivate_memcg_cache_rcu_sched() which slub
can use to schedule sched RCU callback instead of performing
synchronize_sched() synchronously while holding cgroup_mutex.  While
this adds online cpus, mems and slab_mutex operations, operating on
these locks back-to-back from the same kworker, which is what's gonna
happen when there are many to deactivate, isn't expensive at all and
this gets rid of the scalability problem completely.

Link: http://lkml.kernel.org/r/20170117235411.9408-9-tj@kernel.org
Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Jay Vana <jsvana@fb.com>
Acked-by: Vladimir Davydov <vdavydov.dev@gmail.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2017-02-22 16:41:27 -08:00
Tejun Heo c9fc586403 slab: introduce __kmemcg_cache_deactivate()
__kmem_cache_shrink() is called with %true @deactivate only for memcg
caches.  Remove @deactivate from __kmem_cache_shrink() and introduce
__kmemcg_cache_deactivate() instead.  Each memcg-supporting allocator
should implement it and it should deactivate and drain the cache.

This is to allow memcg cache deactivation behavior to further deviate
from simple shrinking without messing up __kmem_cache_shrink().

This is pure reorganization and doesn't introduce any observable
behavior changes.

v2: Dropped unnecessary ifdef in mm/slab.h as suggested by Vladimir.

Link: http://lkml.kernel.org/r/20170117235411.9408-8-tj@kernel.org
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Vladimir Davydov <vdavydov.dev@gmail.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2017-02-22 16:41:27 -08:00
Tejun Heo 510ded33e0 slab: implement slab_root_caches list
With kmem cgroup support enabled, kmem_caches can be created and
destroyed frequently and a great number of near empty kmem_caches can
accumulate if there are a lot of transient cgroups and the system is not
under memory pressure.  When memory reclaim starts under such
conditions, it can lead to consecutive deactivation and destruction of
many kmem_caches, easily hundreds of thousands on moderately large
systems, exposing scalability issues in the current slab management
code.  This is one of the patches to address the issue.

slab_caches currently lists all caches including root and memcg ones.
This is the only data structure which lists the root caches and
iterating root caches can only be done by walking the list while
skipping over memcg caches.  As there can be a huge number of memcg
caches, this can become very expensive.

This also can make /proc/slabinfo behave very badly.  seq_file processes
reads in 4k chunks and seeks to the previous Nth position on slab_caches
list to resume after each chunk.  With a lot of memcg cache churns on
the list, reading /proc/slabinfo can become very slow and its content
often ends up with duplicate and/or missing entries.

This patch adds a new list slab_root_caches which lists only the root
caches.  When memcg is not enabled, it becomes just an alias of
slab_caches.  memcg specific list operations are collected into
memcg_[un]link_cache().

Link: http://lkml.kernel.org/r/20170117235411.9408-7-tj@kernel.org
Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Jay Vana <jsvana@fb.com>
Acked-by: Vladimir Davydov <vdavydov@tarantool.org>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2017-02-22 16:41:27 -08:00
Tejun Heo bc2791f857 slab: link memcg kmem_caches on their associated memory cgroup
With kmem cgroup support enabled, kmem_caches can be created and
destroyed frequently and a great number of near empty kmem_caches can
accumulate if there are a lot of transient cgroups and the system is not
under memory pressure.  When memory reclaim starts under such
conditions, it can lead to consecutive deactivation and destruction of
many kmem_caches, easily hundreds of thousands on moderately large
systems, exposing scalability issues in the current slab management
code.  This is one of the patches to address the issue.

While a memcg kmem_cache is listed on its root cache's ->children list,
there is no direct way to iterate all kmem_caches which are assocaited
with a memory cgroup.  The only way to iterate them is walking all
caches while filtering out caches which don't match, which would be most
of them.

This makes memcg destruction operations O(N^2) where N is the total
number of slab caches which can be huge.  This combined with the
synchronous RCU operations can tie up a CPU and affect the whole machine
for many hours when memory reclaim triggers offlining and destruction of
the stale memcgs.

This patch adds mem_cgroup->kmem_caches list which goes through
memcg_cache_params->kmem_caches_node of all kmem_caches which are
associated with the memcg.  All memcg specific iterations, including
stat file access, are updated to use the new list instead.

Link: http://lkml.kernel.org/r/20170117235411.9408-6-tj@kernel.org
Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Jay Vana <jsvana@fb.com>
Acked-by: Vladimir Davydov <vdavydov.dev@gmail.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2017-02-22 16:41:27 -08:00
Tejun Heo 9eeadc8b6e slab: reorganize memcg_cache_params
We're going to change how memcg caches are iterated.  In preparation,
clean up and reorganize memcg_cache_params.

* The shared ->list is replaced by ->children in root and
  ->children_node in children.

* ->is_root_cache is removed.  Instead ->root_cache is moved out of
  the child union and now used by both root and children.  NULL
  indicates root cache.  Non-NULL a memcg one.

This patch doesn't cause any observable behavior changes.

Link: http://lkml.kernel.org/r/20170117235411.9408-5-tj@kernel.org
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Vladimir Davydov <vdavydov.dev@gmail.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2017-02-22 16:41:27 -08:00
Tejun Heo 290b6a58b7 Revert "slub: move synchronize_sched out of slab_mutex on shrink"
Patch series "slab: make memcg slab destruction scalable", v3.

With kmem cgroup support enabled, kmem_caches can be created and
destroyed frequently and a great number of near empty kmem_caches can
accumulate if there are a lot of transient cgroups and the system is not
under memory pressure.  When memory reclaim starts under such
conditions, it can lead to consecutive deactivation and destruction of
many kmem_caches, easily hundreds of thousands on moderately large
systems, exposing scalability issues in the current slab management
code.

I've seen machines which end up with hundred thousands of caches and
many millions of kernfs_nodes.  The current code is O(N^2) on the total
number of caches and has synchronous rcu_barrier() and
synchronize_sched() in cgroup offline / release path which is executed
while holding cgroup_mutex.  Combined, this leads to very expensive and
slow cache destruction operations which can easily keep running for half
a day.

This also messes up /proc/slabinfo along with other cache iterating
operations.  seq_file operates on 4k chunks and on each 4k boundary
tries to seek to the last position in the list.  With a huge number of
caches on the list, this becomes very slow and very prone to the list
content changing underneath it leading to a lot of missing and/or
duplicate entries.

This patchset addresses the scalability problem.

* Add root and per-memcg lists.  Update each user to use the
  appropriate list.

* Make rcu_barrier() for SLAB_DESTROY_BY_RCU caches globally batched
  and asynchronous.

* For dying empty slub caches, remove the sysfs files after
  deactivation so that we don't end up with millions of sysfs files
  without any useful information on them.

This patchset contains the following nine patches.

 0001-Revert-slub-move-synchronize_sched-out-of-slab_mutex.patch
 0002-slub-separate-out-sysfs_slab_release-from-sysfs_slab.patch
 0003-slab-remove-synchronous-rcu_barrier-call-in-memcg-ca.patch
 0004-slab-reorganize-memcg_cache_params.patch
 0005-slab-link-memcg-kmem_caches-on-their-associated-memo.patch
 0006-slab-implement-slab_root_caches-list.patch
 0007-slab-introduce-__kmemcg_cache_deactivate.patch
 0008-slab-remove-synchronous-synchronize_sched-from-memcg.patch
 0009-slab-remove-slub-sysfs-interface-files-early-for-emp.patch
 0010-slab-use-memcg_kmem_cache_wq-for-slab-destruction-op.patch

0001 reverts an existing optimization to prepare for the following
changes.  0002 is a prep patch.  0003 makes rcu_barrier() in release
path batched and asynchronous.  0004-0006 separate out the lists.
0007-0008 replace synchronize_sched() in slub destruction path with
call_rcu_sched().  0009 removes sysfs files early for empty dying
caches.  0010 makes destruction work items use a workqueue with limited
concurrency.

This patch (of 10):

Revert 89e364db71 ("slub: move synchronize_sched out of slab_mutex on
shrink").

With kmem cgroup support enabled, kmem_caches can be created and destroyed
frequently and a great number of near empty kmem_caches can accumulate if
there are a lot of transient cgroups and the system is not under memory
pressure.  When memory reclaim starts under such conditions, it can lead
to consecutive deactivation and destruction of many kmem_caches, easily
hundreds of thousands on moderately large systems, exposing scalability
issues in the current slab management code.  This is one of the patches to
address the issue.

Moving synchronize_sched() out of slab_mutex isn't enough as it's still
inside cgroup_mutex.  The whole deactivation / release path will be
updated to avoid all synchronous RCU operations.  Revert this insufficient
optimization in preparation to ease future changes.

Link: http://lkml.kernel.org/r/20170117235411.9408-2-tj@kernel.org
Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Jay Vana <jsvana@fb.com>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2017-02-22 16:41:27 -08:00
Vlastimil Babka af3b5f8764 mm, slab: rename kmalloc-node cache to kmalloc-<size>
SLAB as part of its bootstrap pre-creates one kmalloc cache that can fit
the kmem_cache_node management structure, and puts it into the generic
kmalloc cache array (e.g. for 128b objects).  The name of this cache is
"kmalloc-node", which is confusing for readers of /proc/slabinfo as the
cache is used for generic allocations (and not just the kmem_cache_node
struct) and it appears as the kmalloc-128 cache is missing.

An easy solution is to use the kmalloc-<size> name when pre-creating the
cache, which we can get from the kmalloc_info array.

Example /proc/slabinfo before the patch:

  ...
  kmalloc-256         1647   1984    256   16    1 : tunables  120   60    8 : slabdata    124    124    828
  kmalloc-192         1974   1974    192   21    1 : tunables  120   60    8 : slabdata     94     94    133
  kmalloc-96          1332   1344    128   32    1 : tunables  120   60    8 : slabdata     42     42    219
  kmalloc-64          2505   5952     64   64    1 : tunables  120   60    8 : slabdata     93     93    715
  kmalloc-32          4278   4464     32  124    1 : tunables  120   60    8 : slabdata     36     36    346
  kmalloc-node        1352   1376    128   32    1 : tunables  120   60    8 : slabdata     43     43     53
  kmem_cache           132    147    192   21    1 : tunables  120   60    8 : slabdata      7      7      0

After the patch:

  ...
  kmalloc-256         1672   2160    256   16    1 : tunables  120   60    8 : slabdata    135    135    807
  kmalloc-192         1992   2016    192   21    1 : tunables  120   60    8 : slabdata     96     96    203
  kmalloc-96          1159   1184    128   32    1 : tunables  120   60    8 : slabdata     37     37    116
  kmalloc-64          2561   4864     64   64    1 : tunables  120   60    8 : slabdata     76     76    785
  kmalloc-32          4253   4340     32  124    1 : tunables  120   60    8 : slabdata     35     35    270
  kmalloc-128         1256   1280    128   32    1 : tunables  120   60    8 : slabdata     40     40     39
  kmem_cache           125    147    192   21    1 : tunables  120   60    8 : slabdata      7      7      0

[vbabka@suse.cz: export the whole kmalloc_info structure instead of just a name accessor, per Christoph Lameter]
  Link: http://lkml.kernel.org/r/54e80303-b814-4232-66d4-95b34d3eb9d0@suse.cz
Link: http://lkml.kernel.org/r/20170203181008.24898-1-vbabka@suse.cz
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: Matthew Wilcox <mawilcox@microsoft.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Christoph Lameter <cl@linux.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2017-02-22 16:41:27 -08:00
David Rientjes bf00bd3458 mm, slab: maintain total slab count instead of active count
Rather than tracking the number of active slabs for each node, track the
total number of slabs.  This is a minor improvement that avoids active
slab tracking when a slab goes from free to partial or partial to free.

For slab debugging, this also removes an explicit free count since it
can easily be inferred by the difference in number of total objects and
number of active objects.

Link: http://lkml.kernel.org/r/alpine.DEB.2.10.1612042020110.115755@chino.kir.corp.google.com
Signed-off-by: David Rientjes <rientjes@google.com>
Suggested-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Greg Thelen <gthelen@google.com>
Cc: Aruna Ramakrishna <aruna.ramakrishna@oracle.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2016-12-12 18:55:07 -08:00
Greg Thelen f728b0a5d7 mm, slab: faster active and free stats
Reading /proc/slabinfo or monitoring slabtop(1) can become very
expensive if there are many slab caches and if there are very lengthy
per-node partial and/or free lists.

Commit 07a63c41fa ("mm/slab: improve performance of gathering slabinfo
stats") addressed the per-node full lists which showed a significant
improvement when no objects were freed.  This patch has the same
motivation and optimizes the remainder of the usecases where there are
very lengthy partial and free lists.

This patch maintains per-node active_slabs (full and partial) and
free_slabs rather than iterating the lists at runtime when reading
/proc/slabinfo.

When allocating 100GB of slab from a test cache where every slab page is
on the partial list, reading /proc/slabinfo (includes all other slab
caches on the system) takes ~247ms on average with 48 samples.

As a result of this patch, the same read takes ~0.856ms on average.

[rientjes@google.com: changelog]
Link: http://lkml.kernel.org/r/alpine.DEB.2.10.1611081505240.13403@chino.kir.corp.google.com
Signed-off-by: Greg Thelen <gthelen@google.com>
Signed-off-by: David Rientjes <rientjes@google.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2016-12-12 18:55:06 -08:00
Thomas Garnier e70954fd6d mm/slab_common.c: check kmem_create_cache flags are common
Verify that kmem_create_cache flags are not allocator specific.  It is
done before removing flags that are not available with the current
configuration.

The current kmem_cache_create removes incorrect flags but do not
validate the callers are using them right.  This change will ensure that
callers are not trying to create caches with flags that won't be used
because allocator specific.

Link: http://lkml.kernel.org/r/1478553075-120242-2-git-send-email-thgarnie@google.com
Signed-off-by: Thomas Garnier <thgarnie@google.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2016-12-12 18:55:06 -08:00
Vladimir Davydov 89e364db71 slub: move synchronize_sched out of slab_mutex on shrink
synchronize_sched() is a heavy operation and calling it per each cache
owned by a memory cgroup being destroyed may take quite some time.  What
is worse, it's currently called under the slab_mutex, stalling all works
doing cache creation/destruction.

Actually, there isn't much point in calling synchronize_sched() for each
cache - it's enough to call it just once - after setting cpu_partial for
all caches and before shrinking them.  This way, we can also move it out
of the slab_mutex, which we have to hold for iterating over the slab
cache list.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=172991
Link: http://lkml.kernel.org/r/0a10d71ecae3db00fb4421bcd3f82bcc911f4be4.1475329751.git.vdavydov.dev@gmail.com
Signed-off-by: Vladimir Davydov <vdavydov.dev@gmail.com>
Reported-by: Doug Smythies <dsmythies@telus.net>
Acked-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Pekka Enberg <penberg@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2016-12-12 18:55:06 -08:00
Aruna Ramakrishna 07a63c41fa mm/slab: improve performance of gathering slabinfo stats
On large systems, when some slab caches grow to millions of objects (and
many gigabytes), running 'cat /proc/slabinfo' can take up to 1-2
seconds.  During this time, interrupts are disabled while walking the
slab lists (slabs_full, slabs_partial, and slabs_free) for each node,
and this sometimes causes timeouts in other drivers (for instance,
Infiniband).

This patch optimizes 'cat /proc/slabinfo' by maintaining a counter for
total number of allocated slabs per node, per cache.  This counter is
updated when a slab is created or destroyed.  This enables us to skip
traversing the slabs_full list while gathering slabinfo statistics, and
since slabs_full tends to be the biggest list when the cache is large,
it results in a dramatic performance improvement.  Getting slabinfo
statistics now only requires walking the slabs_free and slabs_partial
lists, and those lists are usually much smaller than slabs_full.

We tested this after growing the dentry cache to 70GB, and the
performance improved from 2s to 5ms.

Link: http://lkml.kernel.org/r/1472517876-26814-1-git-send-email-aruna.ramakrishna@oracle.com
Signed-off-by: Aruna Ramakrishna <aruna.ramakrishna@oracle.com>
Acked-by: David Rientjes <rientjes@google.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2016-10-27 18:43:43 -07:00
Alexander Potapenko 80a9201a59 mm, kasan: switch SLUB to stackdepot, enable memory quarantine for SLUB
For KASAN builds:
 - switch SLUB allocator to using stackdepot instead of storing the
   allocation/deallocation stacks in the objects;
 - change the freelist hook so that parts of the freelist can be put
   into the quarantine.

[aryabinin@virtuozzo.com: fixes]
  Link: http://lkml.kernel.org/r/1468601423-28676-1-git-send-email-aryabinin@virtuozzo.com
Link: http://lkml.kernel.org/r/1468347165-41906-3-git-send-email-glider@google.com
Signed-off-by: Alexander Potapenko <glider@google.com>
Cc: Andrey Konovalov <adech.fo@gmail.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Steven Rostedt (Red Hat) <rostedt@goodmis.org>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Kostya Serebryany <kcc@google.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Kuthonuzo Luruo <kuthonuzo.luruo@hpe.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2016-07-28 16:07:41 -07:00
Vladimir Davydov 452647784b mm: memcontrol: cleanup kmem charge functions
- Handle memcg_kmem_enabled check out to the caller. This reduces the
   number of function definitions making the code easier to follow. At
   the same time it doesn't result in code bloat, because all of these
   functions are used only in one or two places.

 - Move __GFP_ACCOUNT check to the caller as well so that one wouldn't
   have to dive deep into memcg implementation to see which allocations
   are charged and which are not.

 - Refresh comments.

Link: http://lkml.kernel.org/r/52882a28b542c1979fd9a033b4dc8637fc347399.1464079537.git.vdavydov@virtuozzo.com
Signed-off-by: Vladimir Davydov <vdavydov@virtuozzo.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Minchan Kim <minchan@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2016-07-26 16:19:19 -07:00
Thomas Garnier 7c00fce98c mm: reorganize SLAB freelist randomization
The kernel heap allocators are using a sequential freelist making their
allocation predictable.  This predictability makes kernel heap overflow
easier to exploit.  An attacker can careful prepare the kernel heap to
control the following chunk overflowed.

For example these attacks exploit the predictability of the heap:
 - Linux Kernel CAN SLUB overflow (https://goo.gl/oMNWkU)
 - Exploiting Linux Kernel Heap corruptions (http://goo.gl/EXLn95)

***Problems that needed solving:
 - Randomize the Freelist (singled linked) used in the SLUB allocator.
 - Ensure good performance to encourage usage.
 - Get best entropy in early boot stage.

***Parts:
 - 01/02 Reorganize the SLAB Freelist randomization to share elements
   with the SLUB implementation.
 - 02/02 The SLUB Freelist randomization implementation. Similar approach
   than the SLAB but tailored to the singled freelist used in SLUB.

***Performance data:

slab_test impact is between 3% to 4% on average for 100000 attempts
without smp.  It is a very focused testing, kernbench show the overall
impact on the system is way lower.

Before:

  Single thread testing
  =====================
  1. Kmalloc: Repeatedly allocate then free test
  100000 times kmalloc(8) -> 49 cycles kfree -> 77 cycles
  100000 times kmalloc(16) -> 51 cycles kfree -> 79 cycles
  100000 times kmalloc(32) -> 53 cycles kfree -> 83 cycles
  100000 times kmalloc(64) -> 62 cycles kfree -> 90 cycles
  100000 times kmalloc(128) -> 81 cycles kfree -> 97 cycles
  100000 times kmalloc(256) -> 98 cycles kfree -> 121 cycles
  100000 times kmalloc(512) -> 95 cycles kfree -> 122 cycles
  100000 times kmalloc(1024) -> 96 cycles kfree -> 126 cycles
  100000 times kmalloc(2048) -> 115 cycles kfree -> 140 cycles
  100000 times kmalloc(4096) -> 149 cycles kfree -> 171 cycles
  2. Kmalloc: alloc/free test
  100000 times kmalloc(8)/kfree -> 70 cycles
  100000 times kmalloc(16)/kfree -> 70 cycles
  100000 times kmalloc(32)/kfree -> 70 cycles
  100000 times kmalloc(64)/kfree -> 70 cycles
  100000 times kmalloc(128)/kfree -> 70 cycles
  100000 times kmalloc(256)/kfree -> 69 cycles
  100000 times kmalloc(512)/kfree -> 70 cycles
  100000 times kmalloc(1024)/kfree -> 73 cycles
  100000 times kmalloc(2048)/kfree -> 72 cycles
  100000 times kmalloc(4096)/kfree -> 71 cycles

After:

  Single thread testing
  =====================
  1. Kmalloc: Repeatedly allocate then free test
  100000 times kmalloc(8) -> 57 cycles kfree -> 78 cycles
  100000 times kmalloc(16) -> 61 cycles kfree -> 81 cycles
  100000 times kmalloc(32) -> 76 cycles kfree -> 93 cycles
  100000 times kmalloc(64) -> 83 cycles kfree -> 94 cycles
  100000 times kmalloc(128) -> 106 cycles kfree -> 107 cycles
  100000 times kmalloc(256) -> 118 cycles kfree -> 117 cycles
  100000 times kmalloc(512) -> 114 cycles kfree -> 116 cycles
  100000 times kmalloc(1024) -> 115 cycles kfree -> 118 cycles
  100000 times kmalloc(2048) -> 147 cycles kfree -> 131 cycles
  100000 times kmalloc(4096) -> 214 cycles kfree -> 161 cycles
  2. Kmalloc: alloc/free test
  100000 times kmalloc(8)/kfree -> 66 cycles
  100000 times kmalloc(16)/kfree -> 66 cycles
  100000 times kmalloc(32)/kfree -> 66 cycles
  100000 times kmalloc(64)/kfree -> 66 cycles
  100000 times kmalloc(128)/kfree -> 65 cycles
  100000 times kmalloc(256)/kfree -> 67 cycles
  100000 times kmalloc(512)/kfree -> 67 cycles
  100000 times kmalloc(1024)/kfree -> 64 cycles
  100000 times kmalloc(2048)/kfree -> 67 cycles
  100000 times kmalloc(4096)/kfree -> 67 cycles

Kernbench, before:

  Average Optimal load -j 12 Run (std deviation):
  Elapsed Time 101.873 (1.16069)
  User Time 1045.22 (1.60447)
  System Time 88.969 (0.559195)
  Percent CPU 1112.9 (13.8279)
  Context Switches 189140 (2282.15)
  Sleeps 99008.6 (768.091)

After:

  Average Optimal load -j 12 Run (std deviation):
  Elapsed Time 102.47 (0.562732)
  User Time 1045.3 (1.34263)
  System Time 88.311 (0.342554)
  Percent CPU 1105.8 (6.49444)
  Context Switches 189081 (2355.78)
  Sleeps 99231.5 (800.358)

This patch (of 2):

This commit reorganizes the previous SLAB freelist randomization to
prepare for the SLUB implementation.  It moves functions that will be
shared to slab_common.

The entropy functions are changed to align with the SLUB implementation,
now using get_random_(int|long) functions.  These functions were chosen
because they provide a bit more entropy early on boot and better
performance when specific arch instructions are not available.

[akpm@linux-foundation.org: fix build]
Link: http://lkml.kernel.org/r/1464295031-26375-2-git-send-email-thgarnie@google.com
Signed-off-by: Thomas Garnier <thgarnie@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2016-07-26 16:19:19 -07:00
Alexander Potapenko 55834c5909 mm: kasan: initial memory quarantine implementation
Quarantine isolates freed objects in a separate queue.  The objects are
returned to the allocator later, which helps to detect use-after-free
errors.

When the object is freed, its state changes from KASAN_STATE_ALLOC to
KASAN_STATE_QUARANTINE.  The object is poisoned and put into quarantine
instead of being returned to the allocator, therefore every subsequent
access to that object triggers a KASAN error, and the error handler is
able to say where the object has been allocated and deallocated.

When it's time for the object to leave quarantine, its state becomes
KASAN_STATE_FREE and it's returned to the allocator.  From now on the
allocator may reuse it for another allocation.  Before that happens,
it's still possible to detect a use-after free on that object (it
retains the allocation/deallocation stacks).

When the allocator reuses this object, the shadow is unpoisoned and old
allocation/deallocation stacks are wiped.  Therefore a use of this
object, even an incorrect one, won't trigger ASan warning.

Without the quarantine, it's not guaranteed that the objects aren't
reused immediately, that's why the probability of catching a
use-after-free is lower than with quarantine in place.

Quarantine isolates freed objects in a separate queue.  The objects are
returned to the allocator later, which helps to detect use-after-free
errors.

Freed objects are first added to per-cpu quarantine queues.  When a
cache is destroyed or memory shrinking is requested, the objects are
moved into the global quarantine queue.  Whenever a kmalloc call allows
memory reclaiming, the oldest objects are popped out of the global queue
until the total size of objects in quarantine is less than 3/4 of the
maximum quarantine size (which is a fraction of installed physical
memory).

As long as an object remains in the quarantine, KASAN is able to report
accesses to it, so the chance of reporting a use-after-free is
increased.  Once the object leaves quarantine, the allocator may reuse
it, in which case the object is unpoisoned and KASAN can't detect
incorrect accesses to it.

Right now quarantine support is only enabled in SLAB allocator.
Unification of KASAN features in SLAB and SLUB will be done later.

This patch is based on the "mm: kasan: quarantine" patch originally
prepared by Dmitry Chernenkov.  A number of improvements have been
suggested by Andrey Ryabinin.

[glider@google.com: v9]
  Link: http://lkml.kernel.org/r/1462987130-144092-1-git-send-email-glider@google.com
Signed-off-by: Alexander Potapenko <glider@google.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Andrey Konovalov <adech.fo@gmail.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Konstantin Serebryany <kcc@google.com>
Cc: Dmitry Chernenkov <dmitryc@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2016-05-20 17:58:30 -07:00
Alexander Potapenko 505f5dcb1c mm, kasan: add GFP flags to KASAN API
Add GFP flags to KASAN hooks for future patches to use.

This patch is based on the "mm: kasan: unified support for SLUB and SLAB
allocators" patch originally prepared by Dmitry Chernenkov.

Signed-off-by: Alexander Potapenko <glider@google.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Andrey Konovalov <adech.fo@gmail.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Konstantin Serebryany <kcc@google.com>
Cc: Dmitry Chernenkov <dmitryc@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2016-03-25 16:37:42 -07:00
Vladimir Davydov 27ee57c93f mm: memcontrol: report slab usage in cgroup2 memory.stat
Show how much memory is used for storing reclaimable and unreclaimable
in-kernel data structures allocated from slab caches.

Signed-off-by: Vladimir Davydov <vdavydov@virtuozzo.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2016-03-17 15:09:34 -07:00
Laura Abbott becfda68ab slub: convert SLAB_DEBUG_FREE to SLAB_CONSISTENCY_CHECKS
SLAB_DEBUG_FREE allows expensive consistency checks at free to be turned
on or off.  Expand its use to be able to turn off all consistency
checks.  This gives a nice speed up if you only want features such as
poisoning or tracing.

Credit to Mathias Krause for the original work which inspired this
series

Signed-off-by: Laura Abbott <labbott@fedoraproject.org>
Acked-by: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <js1304@gmail.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Mathias Krause <minipli@googlemail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2016-03-15 16:55:16 -07:00
Jesper Dangaard Brouer 9f706d6820 mm: fix some spelling
Fix up trivial spelling errors, noticed while reading the code.

Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Vladimir Davydov <vdavydov@virtuozzo.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2016-03-15 16:55:16 -07:00
Jesper Dangaard Brouer fab9963a69 mm: fault-inject take over bootstrap kmem_cache check
Remove the SLAB specific function slab_should_failslab(), by moving the
check against fault-injection for the bootstrap slab, into the shared
function should_failslab() (used by both SLAB and SLUB).

This is a step towards sharing alloc_hook's between SLUB and SLAB.

This bootstrap slab "kmem_cache" is used for allocating struct
kmem_cache objects to the allocator itself.

Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Vladimir Davydov <vdavydov@virtuozzo.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2016-03-15 16:55:16 -07:00
Jesper Dangaard Brouer 11c7aec2a9 mm/slab: move SLUB alloc hooks to common mm/slab.h
First step towards sharing alloc_hook's between SLUB and SLAB
allocators.  Move the SLUB allocators *_alloc_hook to the common
mm/slab.h for internal slab definitions.

Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Vladimir Davydov <vdavydov@virtuozzo.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2016-03-15 16:55:16 -07:00
Dmitry Safonov 52b4b950b5 mm: slab: free kmem_cache_node after destroy sysfs file
When slub_debug alloc_calls_show is enabled we will try to track
location and user of slab object on each online node, kmem_cache_node
structure and cpu_cache/cpu_slub shouldn't be freed till there is the
last reference to sysfs file.

This fixes the following panic:

   BUG: unable to handle kernel NULL pointer dereference at 0000000000000020
   IP:  list_locations+0x169/0x4e0
   PGD 257304067 PUD 438456067 PMD 0
   Oops: 0000 [#1] SMP
   CPU: 3 PID: 973074 Comm: cat ve: 0 Not tainted 3.10.0-229.7.2.ovz.9.30-00007-japdoll-dirty #2 9.30
   Hardware name: DEPO Computers To Be Filled By O.E.M./H67DE3, BIOS L1.60c 07/14/2011
   task: ffff88042a5dc5b0 ti: ffff88037f8d8000 task.ti: ffff88037f8d8000
   RIP: list_locations+0x169/0x4e0
   Call Trace:
     alloc_calls_show+0x1d/0x30
     slab_attr_show+0x1b/0x30
     sysfs_read_file+0x9a/0x1a0
     vfs_read+0x9c/0x170
     SyS_read+0x58/0xb0
     system_call_fastpath+0x16/0x1b
   Code: 5e 07 12 00 b9 00 04 00 00 3d 00 04 00 00 0f 4f c1 3d 00 04 00 00 89 45 b0 0f 84 c3 00 00 00 48 63 45 b0 49 8b 9c c4 f8 00 00 00 <48> 8b 43 20 48 85 c0 74 b6 48 89 df e8 46 37 44 00 48 8b 53 10
   CR2: 0000000000000020

Separated __kmem_cache_release from __kmem_cache_shutdown which now
called on slab_kmem_cache_release (after the last reference to sysfs
file object has dropped).

Reintroduced locking in free_partial as sysfs file might access cache's
partial list after shutdowning - partial revert of the commit
69cb8e6b7c ("slub: free slabs without holding locks").  Zap
__remove_partial and use remove_partial (w/o underscores) as
free_partial now takes list_lock which s partial revert for commit
1e4dd9461f ("slub: do not assert not having lock in removing freed
partial")

Signed-off-by: Dmitry Safonov <dsafonov@virtuozzo.com>
Suggested-by: Vladimir Davydov <vdavydov@virtuozzo.com>
Acked-by: Vladimir Davydov <vdavydov@virtuozzo.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2016-02-18 16:23:24 -08:00
Johannes Weiner 127424c86b mm: memcontrol: move kmem accounting code to CONFIG_MEMCG
The cgroup2 memory controller will account important in-kernel memory
consumers per default.  Move all necessary components to CONFIG_MEMCG.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Vladimir Davydov <vdavydov@virtuozzo.com>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2016-01-20 17:09:18 -08:00
Vladimir Davydov 230e9fc286 slab: add SLAB_ACCOUNT flag
Currently, if we want to account all objects of a particular kmem cache,
we have to pass __GFP_ACCOUNT to each kmem_cache_alloc call, which is
inconvenient.  This patch introduces SLAB_ACCOUNT flag which if passed
to kmem_cache_create will force accounting for every allocation from
this cache even if __GFP_ACCOUNT is not passed.

This patch does not make any of the existing caches use this flag - it
will be done later in the series.

Note, a cache with SLAB_ACCOUNT cannot be merged with a cache w/o
SLAB_ACCOUNT, because merged caches share the same kmem_cache struct and
hence cannot have different sets of SLAB_* flags.  Thus using this flag
will probably reduce the number of merged slabs even if kmem accounting
is not used (only compiled in).

Signed-off-by: Vladimir Davydov <vdavydov@virtuozzo.com>
Suggested-by: Tejun Heo <tj@kernel.org>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Greg Thelen <gthelen@google.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2016-01-14 16:00:49 -08:00
Jesper Dangaard Brouer 865762a811 slab/slub: adjust kmem_cache_alloc_bulk API
Adjust kmem_cache_alloc_bulk API before we have any real users.

Adjust API to return type 'int' instead of previously type 'bool'.  This
is done to allow future extension of the bulk alloc API.

A future extension could be to allow SLUB to stop at a page boundary, when
specified by a flag, and then return the number of objects.

The advantage of this approach, would make it easier to make bulk alloc
run without local IRQs disabled.  With an approach of cmpxchg "stealing"
the entire c->freelist or page->freelist.  To avoid overshooting we would
stop processing at a slab-page boundary.  Else we always end up returning
some objects at the cost of another cmpxchg.

To keep compatible with future users of this API linking against an older
kernel when using the new flag, we need to return the number of allocated
objects with this API change.

Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Cc: Vladimir Davydov <vdavydov@virtuozzo.com>
Acked-by: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2015-11-22 11:58:44 -08:00
Vladimir Davydov f3ccb2c422 memcg: unify slab and other kmem pages charging
We have memcg_kmem_charge and memcg_kmem_uncharge methods for charging and
uncharging kmem pages to memcg, but currently they are not used for
charging slab pages (i.e.  they are only used for charging pages allocated
with alloc_kmem_pages).  The only reason why the slab subsystem uses
special helpers, memcg_charge_slab and memcg_uncharge_slab, is that it
needs to charge to the memcg of kmem cache while memcg_charge_kmem charges
to the memcg that the current task belongs to.

To remove this diversity, this patch adds an extra argument to
__memcg_kmem_charge that can be a pointer to a memcg or NULL.  If it is
not NULL, the function tries to charge to the memcg it points to,
otherwise it charge to the current context.  Next, it makes the slab
subsystem use this function to charge slab pages.

Since memcg_charge_kmem and memcg_uncharge_kmem helpers are now used only
in __memcg_kmem_charge and __memcg_kmem_uncharge, they are inlined.  Since
__memcg_kmem_charge stores a pointer to the memcg in the page struct, we
don't need memcg_uncharge_slab anymore and can use free_kmem_pages.
Besides, one can now detect which memcg a slab page belongs to by reading
/proc/kpagecgroup.

Note, this patch switches slab to charge-after-alloc design.  Since this
design is already used for all other memcg charges, it should not make any
difference.

[hannes@cmpxchg.org: better to have an outer function than a magic parameter for the memcg lookup]
Signed-off-by: Vladimir Davydov <vdavydov@virtuozzo.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2015-11-05 19:34:48 -08:00
Vladimir Davydov d60fdcc9e3 mm/slab_common.c: clear pointers to per memcg caches on destroy
Currently, we do not clear pointers to per memcg caches in the
memcg_params.memcg_caches array when a global cache is destroyed with
kmem_cache_destroy.

This is fine if the global cache does get destroyed.  However, a cache can
be left on the list if it still has active objects when kmem_cache_destroy
is called (due to a memory leak).  If this happens, the entries in the
array will point to already freed areas, which is likely to result in data
corruption when the cache is reused (via slab merging).

Signed-off-by: Vladimir Davydov <vdavydov@virtuozzo.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2015-11-05 19:34:48 -08:00
Daniel Borkmann 2d16e0fd32 mm/slab.h: fix argument order in cache_from_obj's error message
While debugging a networking issue, I hit a condition that triggered an
object to be freed into the wrong kmem cache, and thus triggered the
warning in cache_from_obj().

The arguments in the error message are in wrong order: the location
of the object's kmem cache is in cachep, not s.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2015-09-04 16:54:41 -07:00
Christoph Lameter 484748f0b6 slab: infrastructure for bulk object allocation and freeing
Add the basic infrastructure for alloc/free operations on pointer arrays.
It includes a generic function in the common slab code that is used in
this infrastructure patch to create the unoptimized functionality for slab
bulk operations.

Allocators can then provide optimized allocation functions for situations
in which large numbers of objects are needed.  These optimization may
avoid taking locks repeatedly and bypass metadata creation if all objects
in slab pages can be used to provide the objects required.

Allocators can extend the skeletons provided and add their own code to the
bulk alloc and free functions.  They can keep the generic allocation and
freeing and just fall back to those if optimizations would not work (like
for example when debugging is on).

Signed-off-by: Christoph Lameter <cl@linux.com>
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2015-09-04 16:54:41 -07:00
Daniel Sanders 34cc6990d4 slab: correct size_index table before replacing the bootstrap kmem_cache_node
This patch moves the initialization of the size_index table slightly
earlier so that the first few kmem_cache_node's can be safely allocated
when KMALLOC_MIN_SIZE is large.

There are currently two ways to generate indices into kmalloc_caches (via
kmalloc_index() and via the size_index table in slab_common.c) and on some
arches (possibly only MIPS) they potentially disagree with each other
until create_kmalloc_caches() has been called.  It seems that the
intention is that the size_index table is a fast equivalent to
kmalloc_index() and that create_kmalloc_caches() patches the table to
return the correct value for the cases where kmalloc_index()'s
if-statements apply.

The failing sequence was:
* kmalloc_caches contains NULL elements
* kmem_cache_init initialises the element that 'struct
  kmem_cache_node' will be allocated to. For 32-bit Mips, this is a
  56-byte struct and kmalloc_index returns KMALLOC_SHIFT_LOW (7).
* init_list is called which calls kmalloc_node to allocate a 'struct
  kmem_cache_node'.
* kmalloc_slab selects the kmem_caches element using
  size_index[size_index_elem(size)]. For MIPS, size is 56, and the
  expression returns 6.
* This element of kmalloc_caches is NULL and allocation fails.
* If it had not already failed, it would have called
  create_kmalloc_caches() at this point which would have changed
  size_index[size_index_elem(size)] to 7.

I don't believe the bug to be LLVM specific but GCC doesn't normally
encounter the problem.  I haven't been able to identify exactly what GCC
is doing better (probably inlining) but it seems that GCC is managing to
optimize to the point that it eliminates the problematic allocations.
This theory is supported by the fact that GCC can be made to fail in the
same way by changing inline, __inline, __inline__, and __always_inline in
include/linux/compiler-gcc.h such that they don't actually inline things.

Signed-off-by: Daniel Sanders <daniel.sanders@imgtec.com>
Acked-by: Pekka Enberg <penberg@kernel.org>
Acked-by: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2015-06-24 17:49:41 -07:00
Vladimir Davydov d6e0b7fa11 slub: make dead caches discard free slabs immediately
To speed up further allocations SLUB may store empty slabs in per cpu/node
partial lists instead of freeing them immediately.  This prevents per
memcg caches destruction, because kmem caches created for a memory cgroup
are only destroyed after the last page charged to the cgroup is freed.

To fix this issue, this patch resurrects approach first proposed in [1].
It forbids SLUB to cache empty slabs after the memory cgroup that the
cache belongs to was destroyed.  It is achieved by setting kmem_cache's
cpu_partial and min_partial constants to 0 and tuning put_cpu_partial() so
that it would drop frozen empty slabs immediately if cpu_partial = 0.

The runtime overhead is minimal.  From all the hot functions, we only
touch relatively cold put_cpu_partial(): we make it call
unfreeze_partials() after freezing a slab that belongs to an offline
memory cgroup.  Since slab freezing exists to avoid moving slabs from/to a
partial list on free/alloc, and there can't be allocations from dead
caches, it shouldn't cause any overhead.  We do have to disable preemption
for put_cpu_partial() to achieve that though.

The original patch was accepted well and even merged to the mm tree.
However, I decided to withdraw it due to changes happening to the memcg
core at that time.  I had an idea of introducing per-memcg shrinkers for
kmem caches, but now, as memcg has finally settled down, I do not see it
as an option, because SLUB shrinker would be too costly to call since SLUB
does not keep free slabs on a separate list.  Besides, we currently do not
even call per-memcg shrinkers for offline memcgs.  Overall, it would
introduce much more complexity to both SLUB and memcg than this small
patch.

Regarding to SLAB, there's no problem with it, because it shrinks
per-cpu/node caches periodically.  Thanks to list_lru reparenting, we no
longer keep entries for offline cgroups in per-memcg arrays (such as
memcg_cache_params->memcg_caches), so we do not have to bother if a
per-memcg cache will be shrunk a bit later than it could be.

[1] http://thread.gmane.org/gmane.linux.kernel.mm/118649/focus=118650

Signed-off-by: Vladimir Davydov <vdavydov@parallels.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2015-02-12 18:54:10 -08:00
Vladimir Davydov 426589f571 slab: link memcg caches of the same kind into a list
Sometimes, we need to iterate over all memcg copies of a particular root
kmem cache.  Currently, we use memcg_cache_params->memcg_caches array for
that, because it contains all existing memcg caches.

However, it's a bad practice to keep all caches, including those that
belong to offline cgroups, in this array, because it will be growing
beyond any bounds then.  I'm going to wipe away dead caches from it to
save space.  To still be able to perform iterations over all memcg caches
of the same kind, let us link them into a list.

Signed-off-by: Vladimir Davydov <vdavydov@parallels.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Tejun Heo <tj@kernel.org>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Dave Chinner <david@fromorbit.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2015-02-12 18:54:09 -08:00
Vladimir Davydov f7ce3190c4 slab: embed memcg_cache_params to kmem_cache
Currently, kmem_cache stores a pointer to struct memcg_cache_params
instead of embedding it.  The rationale is to save memory when kmem
accounting is disabled.  However, the memcg_cache_params has shrivelled
drastically since it was first introduced:

* Initially:

struct memcg_cache_params {
	bool is_root_cache;
	union {
		struct kmem_cache *memcg_caches[0];
		struct {
			struct mem_cgroup *memcg;
			struct list_head list;
			struct kmem_cache *root_cache;
			bool dead;
			atomic_t nr_pages;
			struct work_struct destroy;
		};
	};
};

* Now:

struct memcg_cache_params {
	bool is_root_cache;
	union {
		struct {
			struct rcu_head rcu_head;
			struct kmem_cache *memcg_caches[0];
		};
		struct {
			struct mem_cgroup *memcg;
			struct kmem_cache *root_cache;
		};
	};
};

So the memory saving does not seem to be a clear win anymore.

OTOH, keeping a pointer to memcg_cache_params struct instead of embedding
it results in touching one more cache line on kmem alloc/free hot paths.
Besides, it makes linking kmem caches in a list chained by a field of
struct memcg_cache_params really painful due to a level of indirection,
while I want to make them linked in the following patch.  That said, let
us embed it.

Signed-off-by: Vladimir Davydov <vdavydov@parallels.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Tejun Heo <tj@kernel.org>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2015-02-12 18:54:09 -08:00
Vladimir Davydov dbf22eb6d8 memcg: zap __memcg_{charge,uncharge}_slab
They are simple wrappers around memcg_{charge,uncharge}_kmem, so let's
zap them and call these functions directly.

Signed-off-by: Vladimir Davydov <vdavydov@parallels.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2015-02-10 14:30:34 -08:00
Vladimir Davydov b047501cd9 memcg: use generic slab iterators for showing slabinfo
Let's use generic slab_start/next/stop for showing memcg caches info.  In
contrast to the current implementation, this will work even if all memcg
caches' info doesn't fit into a seq buffer (a page), plus it simply looks
neater.

Actually, the main reason I do this isn't mere cleanup.  I'm going to zap
the memcg_slab_caches list, because I find it useless provided we have the
slab_caches list, and this patch is a step in this direction.

It should be noted that before this patch an attempt to read
memory.kmem.slabinfo of a cgroup that doesn't have kmem limit set resulted
in -EIO, while after this patch it will silently show nothing except the
header, but I don't think it will frustrate anyone.

Signed-off-by: Vladimir Davydov <vdavydov@parallels.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-12-10 17:41:07 -08:00
Pranith Kumar 8df0c2dcf6 slab: replace smp_read_barrier_depends() with lockless_dereference()
Recently lockless_dereference() was added which can be used in place of
hard-coding smp_read_barrier_depends().  The following PATCH makes the
change.

Signed-off-by: Pranith Kumar <bobby.prani@gmail.com>
Cc: "Paul E. McKenney" <paulmck@us.ibm.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-12-10 17:41:04 -08:00
Vladimir Davydov 1df3b26f20 slab: print slabinfo header in seq show
Currently we print the slabinfo header in the seq start method, which
makes it unusable for showing leaks, so we have leaks_show, which does
practically the same as s_show except it doesn't show the header.

However, we can print the header in the seq show method - we only need
to check if the current element is the first on the list.  This will
allow us to use the same set of seq iterators for both leaks and
slabinfo reporting, which is nice.

Signed-off-by: Vladimir Davydov <vdavydov@parallels.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-12-10 17:41:04 -08:00
Joonsoo Kim bf0dea23a9 mm/slab: use percpu allocator for cpu cache
Because of chicken and egg problem, initialization of SLAB is really
complicated.  We need to allocate cpu cache through SLAB to make the
kmem_cache work, but before initialization of kmem_cache, allocation
through SLAB is impossible.

On the other hand, SLUB does initialization in a more simple way.  It uses
percpu allocator to allocate cpu cache so there is no chicken and egg
problem.

So, this patch try to use percpu allocator in SLAB.  This simplifies the
initialization step in SLAB so that we could maintain SLAB code more
easily.

In my testing there is no performance difference.

This implementation relies on percpu allocator.  Because percpu allocator
uses vmalloc address space, vmalloc address space could be exhausted by
this change on many cpu system with *32 bit* kernel.  This implementation
can cover 1024 cpus in worst case by following calculation.

Worst: 1024 cpus * 4 bytes for pointer * 300 kmem_caches *
	120 objects per cpu_cache = 140 MB
Normal: 1024 cpus * 4 bytes for pointer * 150 kmem_caches(slab merge) *
	80 objects per cpu_cache = 46 MB

Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Acked-by: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Jeremiah Mahler <jmmahler@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-10-09 22:25:51 -04:00
Joonsoo Kim 12220dea07 mm/slab: support slab merge
Slab merge is good feature to reduce fragmentation.  If new creating slab
have similar size and property with exsitent slab, this feature reuse it
rather than creating new one.  As a result, objects are packed into fewer
slabs so that fragmentation is reduced.

Below is result of my testing.

* After boot, sleep 20; cat /proc/meminfo | grep Slab

<Before>
Slab: 25136 kB

<After>
Slab: 24364 kB

We can save 3% memory used by slab.

For supporting this feature in SLAB, we need to implement SLAB specific
kmem_cache_flag() and __kmem_cache_alias(), because SLUB implements some
SLUB specific processing related to debug flag and object size change on
these functions.

Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-10-09 22:25:51 -04:00
Joonsoo Kim 423c929cbb mm/slab_common: commonize slab merge logic
Slab merge is good feature to reduce fragmentation.  Now, it is only
applied to SLUB, but, it would be good to apply it to SLAB.  This patch is
preparation step to apply slab merge to SLAB by commonizing slab merge
logic.

Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-10-09 22:25:51 -04:00
Mikulas Patocka 9163582c3f slab: fix for_each_kmem_cache_node()
Fix a bug (discovered with kmemcheck) in for_each_kmem_cache_node().  The
for loop reads the array "node" before verifying that the index is within
the range.  This results in kmemcheck warning.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Reviewed-by: Pekka Enberg <penberg@kernel.org>
Acked-by: Christoph Lameter <cl@linux.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-10-09 22:25:51 -04:00
Joonsoo Kim 07f361b2be mm/slab_common: move kmem_cache definition to internal header
We don't need to keep kmem_cache definition in include/linux/slab.h if we
don't need to inline kmem_cache_size().  According to my code inspection,
this function is only called at lc_create() in lib/lru_cache.c which may
be called at initialization phase of something, so we don't need to inline
it.  Therfore, move it to slab_common.c and move kmem_cache definition to
internal header.

After this change, we can change kmem_cache definition easily without full
kernel build.  For instance, we can turn on/off CONFIG_SLUB_STATS without
full kernel build.

[akpm@linux-foundation.org: export kmem_cache_size() to modules]
[rdunlap@infradead.org: add header files to fix kmemcheck.c build errors]
Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Acked-by: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Zhang Yanfei <zhangyanfei@cn.fujitsu.com>
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-10-09 22:25:50 -04:00
Joe Perches c42e571561 slab: convert last use of __FUNCTION__ to __func__
Just about all of these have been converted to __func__, so convert the
last use.

Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-08-06 18:01:15 -07:00
Joonsoo Kim c8522a3a58 slab: introduce alien_cache
Currently, we use array_cache for alien_cache.  Although they are mostly
similar, there is one difference, that is, need for spinlock.  We don't
need spinlock for array_cache itself, but to use array_cache for
alien_cache, array_cache structure should have spinlock.  This is
needless overhead, so removing it would be better.  This patch prepare
it by introducing alien_cache and using it.  In the following patch, we
remove spinlock in array_cache.

Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Acked-by: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-08-06 18:01:14 -07:00
Andrey Ryabinin 5240ab4076 mm: slab.h: wrap the whole file with guarding macro
Guarding section:
	#ifndef MM_SLAB_H
	#define MM_SLAB_H
	...
	#endif
currently doesn't cover the whole mm/slab.h. It seems like it was
done unintentionally.

Wrap the whole file by moving closing #endif to the end of it.

Signed-off-by: Andrey Ryabinin <a.ryabinin@samsung.com>
Acked-by: Christoph Lameter <cl@linux.com>
Acked-by: David Rientjes <rientjes@google.com>
Reviewed-by: Vladimir Davydov <vdavydov@parallels.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>

Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-08-06 18:01:14 -07:00
Christoph Lameter 44c5356fb4 slab common: add functions for kmem_cache_node access
The patchset provides two new functions in mm/slab.h and modifies SLAB
and SLUB to use these.  The kmem_cache_node structure is shared between
both allocators and the use of common accessors will allow us to move
more code into slab_common.c in the future.

This patch (of 3):

These functions allow to eliminate repeatedly used code in both SLAB and
SLUB and also allow for the insertion of debugging code that may be
needed in the development process.

Signed-off-by: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Acked-by: David Rientjes <rientjes@google.com>
Acked-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-08-06 18:01:13 -07:00
Vladimir Davydov c67a8a685a memcg, slab: merge memcg_{bind,release}_pages to memcg_{un}charge_slab
Currently we have two pairs of kmemcg-related functions that are called on
slab alloc/free.  The first is memcg_{bind,release}_pages that count the
total number of pages allocated on a kmem cache.  The second is
memcg_{un}charge_slab that {un}charge slab pages to kmemcg resource
counter.  Let's just merge them to keep the code clean.

Signed-off-by: Vladimir Davydov <vdavydov@parallels.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Glauber Costa <glommer@gmail.com>
Cc: Pekka Enberg <penberg@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-06-04 16:54:01 -07:00
Vladimir Davydov 1e32e77f95 memcg, slab: do not schedule cache destruction when last page goes away
This patchset is a part of preparations for kmemcg re-parenting.  It
targets at simplifying kmemcg work-flows and synchronization.

First, it removes async per memcg cache destruction (see patches 1, 2).
Now caches are only destroyed on memcg offline.  That means the caches
that are not empty on memcg offline will be leaked.  However, they are
already leaked, because memcg_cache_params::nr_pages normally never drops
to 0 so the destruction work is never scheduled except kmem_cache_shrink
is called explicitly.  In the future I'm planning reaping such dead caches
on vmpressure or periodically.

Second, it substitutes per memcg slab_caches_mutex's with the global
memcg_slab_mutex, which should be taken during the whole per memcg cache
creation/destruction path before the slab_mutex (see patch 3).  This
greatly simplifies synchronization among various per memcg cache
creation/destruction paths.

I'm still not quite sure about the end picture, in particular I don't know
whether we should reap dead memcgs' kmem caches periodically or try to
merge them with their parents (see https://lkml.org/lkml/2014/4/20/38 for
more details), but whichever way we choose, this set looks like a
reasonable change to me, because it greatly simplifies kmemcg work-flows
and eases further development.

This patch (of 3):

After a memcg is offlined, we mark its kmem caches that cannot be deleted
right now due to pending objects as dead by setting the
memcg_cache_params::dead flag, so that memcg_release_pages will schedule
cache destruction (memcg_cache_params::destroy) as soon as the last slab
of the cache is freed (memcg_cache_params::nr_pages drops to zero).

I guess the idea was to destroy the caches as soon as possible, i.e.
immediately after freeing the last object.  However, it just doesn't work
that way, because kmem caches always preserve some pages for the sake of
performance, so that nr_pages never gets to zero unless the cache is
shrunk explicitly using kmem_cache_shrink.  Of course, we could account
the total number of objects on the cache or check if all the slabs
allocated for the cache are empty on kmem_cache_free and schedule
destruction if so, but that would be too costly.

Thus we have a piece of code that works only when we explicitly call
kmem_cache_shrink, but complicates the whole picture a lot.  Moreover,
it's racy in fact.  For instance, kmem_cache_shrink may free the last slab
and thus schedule cache destruction before it finishes checking that the
cache is empty, which can lead to use-after-free.

So I propose to remove this async cache destruction from
memcg_release_pages, and check if the cache is empty explicitly after
calling kmem_cache_shrink instead.  This will simplify things a lot w/o
introducing any functional changes.

And regarding dead memcg caches (i.e.  those that are left hanging around
after memcg offline for they have objects), I suppose we should reap them
either periodically or on vmpressure as Glauber suggested initially.  I'm
going to implement this later.

Signed-off-by: Vladimir Davydov <vdavydov@parallels.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Glauber Costa <glommer@gmail.com>
Cc: Pekka Enberg <penberg@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-06-04 16:54:01 -07:00