Commit 1ebf26a9 authored Jun 16, 2009 by Wu Fengguang Committed by Linus Torvalds Jun 16, 2009

readahead: make mmap_miss an unsigned int



This makes the performance impact of possible mmap_miss wrap around to be
temporary and tolerable: i.e.  MMAP_LOTSAMISS=100 extra readarounds.

Otherwise if ever mmap_miss wraps around to negative, it takes INT_MAX
cache misses to bring it back to normal state.  During the time mmap
readaround will be _enabled_ for whatever wild random workload.  That's
almost permanent performance impact.

Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
Cc: Ying Han <yinghan@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent bb1f17b0

include/linux/fs.h

+1 −1

Original line number	Diff line number	Diff line
		@@ -879,7 +879,7 @@ struct file_ra_state {
		there are only # of pages ahead */

		unsigned int ra_pages; /* Maximum readahead window */
		int mmap_miss; /* Cache miss stat for mmap accesses */
		unsigned int mmap_miss; /* Cache miss stat for mmap accesses */
		loff_t prev_pos; /* Cache last read() position */
		};