Commit 207d04ba authored May 24, 2011 by Andi Kleen Committed by Linus Torvalds May 25, 2011

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>

parent 275b12bf

mm/filemap.c

+2 −1

Original line number	Original line	Diff line number	Diff line
	@@ -1566,7 +1566,8 @@ static void do_sync_mmap_readahead(struct vm_area_struct *vma,
	return;		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++;		ra->mmap_miss++;

	/*		/*