readahead: reduce unnecessary mmap_miss increases
The original INT_MAX is too large, reduce it to
- avoid unnecessarily dirtying/bouncing the cache line
- restore mmap read-around faster on changed access pattern
Background: in the mosbench exim benchmark which does multi-threaded page
faults on shared struct file, the ra->mmap_miss updates are found to cause
excessive cache line bouncing on tmpfs. The ra state updates are needless
for tmpfs because it actually disabled readahead totally
(shmem_backing_dev_info.ra_pages == 0).
Tested-by: Tim Chen <tim.c.chen@intel.com>
Signed-off-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/filemap.c b/mm/filemap.c
index c974a28..e513139 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1566,7 +1566,8 @@
return;
}
- if (ra->mmap_miss < INT_MAX)
+ /* Avoid banging the cache line if not needed */
+ if (ra->mmap_miss < MMAP_LOTSAMISS * 10)
ra->mmap_miss++;
/*