linux/fs/qnx4
Nick Piggin fa0d7e3de6 fs: icache RCU free inodes
RCU free the struct inode. This will allow:

- Subsequent store-free path walking patch. The inode must be consulted for
  permissions when walking, so an RCU inode reference is a must.
- sb_inode_list_lock to be moved inside i_lock because sb list walkers who want
  to take i_lock no longer need to take sb_inode_list_lock to walk the list in
  the first place. This will simplify and optimize locking.
- Could remove some nested trylock loops in dcache code
- Could potentially simplify things a bit in VM land. Do not need to take the
  page lock to follow page->mapping.

The downsides of this is the performance cost of using RCU. In a simple
creat/unlink microbenchmark, performance drops by about 10% due to inability to
reuse cache-hot slab objects. As iterations increase and RCU freeing starts
kicking over, this increases to about 20%.

In cases where inode lifetimes are longer (ie. many inodes may be allocated
during the average life span of a single inode), a lot of this cache reuse is
not applicable, so the regression caused by this patch is smaller.

The cache-hot regression could largely be avoided by using SLAB_DESTROY_BY_RCU,
however this adds some complexity to list walking and store-free path walking,
so I prefer to implement this at a later date, if it is shown to be a win in
real situations. I haven't found a regression in any non-micro benchmark so I
doubt it will be a problem.

Signed-off-by: Nick Piggin <npiggin@kernel.dk>
2011-01-07 17:50:26 +11:00
..
Kconfig qnx4: remove write support 2009-09-23 07:39:30 -07:00
Makefile qnx4: remove write support 2009-09-23 07:39:30 -07:00
README Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
bitmap.c qnx4: use hweight8 2009-12-16 07:20:18 -08:00
dir.c BKL: remove BKL from qnx4 2010-10-21 18:48:04 +02:00
inode.c fs: icache RCU free inodes 2011-01-07 17:50:26 +11:00
namei.c BKL: remove BKL from qnx4 2010-10-21 18:48:04 +02:00
qnx4.h qnx4: remove write support 2009-09-23 07:39:30 -07:00

README

  This is a snapshot of the QNX4 filesystem for Linux.
  Please send diffs and remarks to <al@alarsen.net> .
  
Credits :

Richard "Scuba" A. Frowijn     <scuba@wxs.nl>
Frank "Jedi/Sector One" Denis  <j@pureftpd.org>
Anders Larsen                  <al@alarsen.net> (Maintainer)