linux/arch/arc/kernel
Michal Hocko 0ee931c4e3 mm: treewide: remove GFP_TEMPORARY allocation flag
GFP_TEMPORARY was introduced by commit e12ba74d8f ("Group short-lived
and reclaimable kernel allocations") along with __GFP_RECLAIMABLE.  It's
primary motivation was to allow users to tell that an allocation is
short lived and so the allocator can try to place such allocations close
together and prevent long term fragmentation.  As much as this sounds
like a reasonable semantic it becomes much less clear when to use the
highlevel GFP_TEMPORARY allocation flag.  How long is temporary? Can the
context holding that memory sleep? Can it take locks? It seems there is
no good answer for those questions.

The current implementation of GFP_TEMPORARY is basically GFP_KERNEL |
__GFP_RECLAIMABLE which in itself is tricky because basically none of
the existing caller provide a way to reclaim the allocated memory.  So
this is rather misleading and hard to evaluate for any benefits.

I have checked some random users and none of them has added the flag
with a specific justification.  I suspect most of them just copied from
other existing users and others just thought it might be a good idea to
use without any measuring.  This suggests that GFP_TEMPORARY just
motivates for cargo cult usage without any reasoning.

I believe that our gfp flags are quite complex already and especially
those with highlevel semantic should be clearly defined to prevent from
confusion and abuse.  Therefore I propose dropping GFP_TEMPORARY and
replace all existing users to simply use GFP_KERNEL.  Please note that
SLAB users with shrinkers will still get __GFP_RECLAIMABLE heuristic and
so they will be placed properly for memory fragmentation prevention.

I can see reasons we might want some gfp flag to reflect shorterm
allocations but I propose starting from a clear semantic definition and
only then add users with proper justification.

This was been brought up before LSF this year by Matthew [1] and it
turned out that GFP_TEMPORARY really doesn't have a clear semantic.  It
seems to be a heuristic without any measured advantage for most (if not
all) its current users.  The follow up discussion has revealed that
opinions on what might be temporary allocation differ a lot between
developers.  So rather than trying to tweak existing users into a
semantic which they haven't expected I propose to simply remove the flag
and start from scratch if we really need a semantic for short term
allocations.

[1] http://lkml.kernel.org/r/20170118054945.GD18349@bombadil.infradead.org

[akpm@linux-foundation.org: fix typo]
[akpm@linux-foundation.org: coding-style fixes]
[sfr@canb.auug.org.au: drm/i915: fix up]
  Link: http://lkml.kernel.org/r/20170816144703.378d4f4d@canb.auug.org.au
Link: http://lkml.kernel.org/r/20170728091904.14627-1-mhocko@kernel.org
Signed-off-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Acked-by: Mel Gorman <mgorman@suse.de>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Neil Brown <neilb@suse.de>
Cc: "Theodore Ts'o" <tytso@mit.edu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2017-09-13 18:53:16 -07:00
..
.gitignore ARC: Add some .gitignore entries 2013-08-26 09:40:24 +05:30
Makefile ARC: Remove empty kernel/pcibios.c 2017-08-02 14:53:35 -05:00
arc_hostlink.c ARC: Hostlink Pseudo-Driver for Metaware Debugger 2013-02-15 23:16:10 +05:30
arcksyms.c ARC: export __udivdi3 for modules 2016-08-19 14:09:33 -07:00
asm-offsets.c ARCv2: [vdk] dts files and defconfig for HS38 VDK 2015-06-25 06:00:21 +05:30
ctx_sw.c sched/headers: Prepare for new header dependencies before moving code to <linux/sched/debug.h> 2017-03-02 08:42:34 +01:00
ctx_sw_asm.S ARC: dw2 unwind: enable cfi pseudo ops in string lib 2016-09-30 14:48:22 -07:00
devtree.c ARC: [plat-hsdk] initial port for HSDK board 2017-09-01 11:26:28 -07:00
disasm.c ARC: rename kconfig option for unaligned emulation 2014-10-13 14:46:15 +05:30
entry-arcv2.S ARCv2: make unimplemented vectors as no-ops rather than halt core 2017-03-20 18:47:57 -07:00
entry-compact.S ARC: typos fix in kernel/entry-compact.S 2017-08-28 15:17:36 -07:00
entry.S ARC: Re-enable MMU upon Machine Check exception 2017-09-01 11:29:05 -07:00
fpu.c ARC: Process-creation/scheduling/idle-loop 2013-02-11 20:00:38 +05:30
head.S ARC: smp-boot: Decouple Non masters waiting API from jump to entry point 2017-01-24 11:12:28 -08:00
intc-arcv2.c ARCv2: SMP: Mask only private-per-core IRQ lines on boot at core intc 2017-08-28 16:11:15 -07:00
intc-compact.c ARCv2: SMP: Mask only private-per-core IRQ lines on boot at core intc 2017-08-28 16:11:15 -07:00
irq.c ARC: [intc-*] Do a domain lookup in primary handler for hwirq -> linux virq 2016-05-09 09:32:30 +05:30
kgdb.c sched/headers: Prepare for new header dependencies before moving code to <linux/sched/task_stack.h> 2017-03-02 08:42:36 +01:00
kprobes.c Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/trivial 2013-11-15 16:47:22 -08:00
mcip.c ARCv2: IDU-intc: Delete deprecated parameters in Device Trees 2017-02-06 09:37:57 -08:00
module.c ARC: module: Fix !CONFIG_ARC_DW2_UNWIND builds 2017-01-18 11:17:44 -08:00
perf_event.c arc: perf: Enable generic "cache-references" and "cache-misses" events 2016-09-30 14:48:18 -07:00
process.c ARC: [plat-eznps] handle extra aux regs #2: kernel/entry exit 2017-08-28 15:17:36 -07:00
ptrace.c ARCv2: ptrace: provide regset for accumulator/r30 regs 2017-05-03 11:21:31 -07:00
reset.c arc: export symbol for pm_power_off in reset.c 2013-11-06 10:41:44 +05:30
setup.c mm: treewide: remove GFP_TEMPORARY allocation flag 2017-09-13 18:53:16 -07:00
signal.c sched/headers: Prepare for new header dependencies before moving code to <linux/sched/task_stack.h> 2017-03-02 08:42:36 +01:00
smp.c sched/headers: Move task->mm handling methods to <linux/sched/mm.h> 2017-03-03 01:43:28 +01:00
stacktrace.c sched/headers: Prepare for new header dependencies before moving code to <linux/sched/debug.h> 2017-03-02 08:42:34 +01:00
sys.c ARC: ABIv3: fork/vfork wrappers not needed in "no-legacy-syscall" ABI 2013-03-11 19:01:10 +05:30
traps.c ARC: Show fault information passed to show_kernel_fault_diag() 2017-09-01 11:26:29 -07:00
troubleshoot.c mm: treewide: remove GFP_TEMPORARY allocation flag 2017-09-13 18:53:16 -07:00
unaligned.c ARC: [arcompact] brown paper bag bug in unaligned access delay slot fixup 2017-02-07 10:02:01 -08:00
unwind.c scripts/spelling.txt: add regsiter -> register spelling mistake 2017-05-08 17:15:13 -07:00
vmlinux.lds.S nmi_backtrace: generate one-line reports for idle cpus 2016-10-07 18:46:30 -07:00