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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>
This commit is contained in:
Wu Fengguang 2009-06-16 15:31:19 -07:00 committed by Linus Torvalds
parent bb1f17b037
commit 1ebf26a9b3
1 changed files with 1 additions and 1 deletions
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2
include/linux/fs.h
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@ -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 */
};