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Mel Gorman 2457aec637 mm: non-atomically mark page accessed during page cache allocation where possible ... aops->write_begin may allocate a new page and make it visible only to have mark_page_accessed called almost immediately after. Once the page is visible the atomic operations are necessary which is noticable overhead when writing to an in-memory filesystem like tmpfs but should also be noticable with fast storage. The objective of the patch is to initialse the accessed information with non-atomic operations before the page is visible. The bulk of filesystems directly or indirectly use grab_cache_page_write_begin or find_or_create_page for the initial allocation of a page cache page. This patch adds an init_page_accessed() helper which behaves like the first call to mark_page_accessed() but may called before the page is visible and can be done non-atomically. The primary APIs of concern in this care are the following and are used by most filesystems. find_get_page find_lock_page find_or_create_page grab_cache_page_nowait grab_cache_page_write_begin All of them are very similar in detail to the patch creates a core helper pagecache_get_page() which takes a flags parameter that affects its behavior such as whether the page should be marked accessed or not. Then old API is preserved but is basically a thin wrapper around this core function. Each of the filesystems are then updated to avoid calling mark_page_accessed when it is known that the VM interfaces have already done the job. There is a slight snag in that the timing of the mark_page_accessed() has now changed so in rare cases it's possible a page gets to the end of the LRU as PageReferenced where as previously it might have been repromoted. This is expected to be rare but it's worth the filesystem people thinking about it in case they see a problem with the timing change. It is also the case that some filesystems may be marking pages accessed that previously did not but it makes sense that filesystems have consistent behaviour in this regard. The test case used to evaulate this is a simple dd of a large file done multiple times with the file deleted on each iterations. The size of the file is 1/10th physical memory to avoid dirty page balancing. In the async case it will be possible that the workload completes without even hitting the disk and will have variable results but highlight the impact of mark_page_accessed for async IO. The sync results are expected to be more stable. The exception is tmpfs where the normal case is for the "IO" to not hit the disk. The test machine was single socket and UMA to avoid any scheduling or NUMA artifacts. Throughput and wall times are presented for sync IO, only wall times are shown for async as the granularity reported by dd and the variability is unsuitable for comparison. As async results were variable do to writback timings, I'm only reporting the maximum figures. The sync results were stable enough to make the mean and stddev uninteresting. The performance results are reported based on a run with no profiling. Profile data is based on a separate run with oprofile running. async dd 3.15.0-rc3 3.15.0-rc3 vanilla accessed-v2 ext3 Max elapsed 13.9900 ( 0.00%) 11.5900 ( 17.16%) tmpfs Max elapsed 0.5100 ( 0.00%) 0.4900 ( 3.92%) btrfs Max elapsed 12.8100 ( 0.00%) 12.7800 ( 0.23%) ext4 Max elapsed 18.6000 ( 0.00%) 13.3400 ( 28.28%) xfs Max elapsed 12.5600 ( 0.00%) 2.0900 ( 83.36%) The XFS figure is a bit strange as it managed to avoid a worst case by sheer luck but the average figures looked reasonable. samples percentage ext3 86107 0.9783 vmlinux-3.15.0-rc4-vanilla mark_page_accessed ext3 23833 0.2710 vmlinux-3.15.0-rc4-accessed-v3r25 mark_page_accessed ext3 5036 0.0573 vmlinux-3.15.0-rc4-accessed-v3r25 init_page_accessed ext4 64566 0.8961 vmlinux-3.15.0-rc4-vanilla mark_page_accessed ext4 5322 0.0713 vmlinux-3.15.0-rc4-accessed-v3r25 mark_page_accessed ext4 2869 0.0384 vmlinux-3.15.0-rc4-accessed-v3r25 init_page_accessed xfs 62126 1.7675 vmlinux-3.15.0-rc4-vanilla mark_page_accessed xfs 1904 0.0554 vmlinux-3.15.0-rc4-accessed-v3r25 init_page_accessed xfs 103 0.0030 vmlinux-3.15.0-rc4-accessed-v3r25 mark_page_accessed btrfs 10655 0.1338 vmlinux-3.15.0-rc4-vanilla mark_page_accessed btrfs 2020 0.0273 vmlinux-3.15.0-rc4-accessed-v3r25 init_page_accessed btrfs 587 0.0079 vmlinux-3.15.0-rc4-accessed-v3r25 mark_page_accessed tmpfs 59562 3.2628 vmlinux-3.15.0-rc4-vanilla mark_page_accessed tmpfs 1210 0.0696 vmlinux-3.15.0-rc4-accessed-v3r25 init_page_accessed tmpfs 94 0.0054 vmlinux-3.15.0-rc4-accessed-v3r25 mark_page_accessed [akpm@linux-foundation.org: don't run init_page_accessed() against an uninitialised pointer] Signed-off-by: Mel Gorman <mgorman@suse.de> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Jan Kara <jack@suse.cz> Cc: Michal Hocko <mhocko@suse.cz> Cc: Hugh Dickins <hughd@google.com> Cc: Dave Hansen <dave.hansen@intel.com> Cc: Theodore Ts'o <tytso@mit.edu> Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Rik van Riel <riel@redhat.com> Cc: Peter Zijlstra <peterz@infradead.org> Tested-by: Prabhakar Lad <prabhakar.csengg@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>		11 years ago
..
Kconfig	…
Makefile	…
acl.c	GFS2: inline function gfs2_set_mode	11 years ago
acl.h	GFS2: Increase the max number of ACLs	11 years ago
aops.c	mm: non-atomically mark page accessed during page cache allocation where possible	11 years ago
bmap.c	GFS2: fs/gfs2/bmap.c: kernel-doc warning fixes	11 years ago
bmap.h	GFS2: Clean up journal extent mapping	11 years ago
dentry.c	…
dir.c	GFS2: Use pr_<level> more consistently	11 years ago
dir.h	…
export.c	…
file.c	GFS2: fs/gfs2/file.c: kernel-doc warning fixes	11 years ago
gfs2.h	…
glock.c	arch: Mass conversion of smp_mb__*()	11 years ago
glock.h	…
glops.c	This must be about the smallest merge window patch set ever for GFS2.	11 years ago
glops.h	GFS2: remove transaction glock	11 years ago
incore.h	GFS2: Prevent recovery before the local journal is set	11 years ago
inode.c	GFS2: remove transaction glock	11 years ago
inode.h	…
lock_dlm.c	arch: Mass conversion of smp_mb__*()	11 years ago
log.c	GFS2: remove transaction glock	11 years ago
log.h	GFS2: remove transaction glock	11 years ago
lops.c	GFS2: lops.c: replace 0 by NULL for pointers	11 years ago
lops.h	GFS2: Move log buffer lists into transaction	11 years ago
main.c	GFS2: Use pr_<level> more consistently	11 years ago
meta_io.c	mm: non-atomically mark page accessed during page cache allocation where possible	11 years ago
meta_io.h	GFS2: Fix address space from page function	11 years ago
ops_fstype.c	GFS2: Prevent recovery before the local journal is set	11 years ago
quota.c	GFS2: remove transaction glock	11 years ago
quota.h	…
recovery.c	This must be about the smallest merge window patch set ever for GFS2.	11 years ago
recovery.h	GFS2: Move recovery variables to journal structure in memory	11 years ago
rgrp.c	GFS2: remove transaction glock	11 years ago
rgrp.h	…
super.c	GFS2: remove transaction glock	11 years ago
super.h	…
sys.c	This must be about the smallest merge window patch set ever for GFS2.	11 years ago
sys.h	…
trace_gfs2.h	…
trans.c	GFS2: remove transaction glock	11 years ago
trans.h	…
util.c	GFS2: Convert gfs2_lm_withdraw to use fs_err	11 years ago
util.h	GFS2: Convert gfs2_lm_withdraw to use fs_err	11 years ago
xattr.c	…
xattr.h	…