From: Andi Kleen <ak@linux.intel.com>
Date: Wed, 25 May 2011 00:12:29 +0000 (-0700)
Subject: readahead: reduce unnecessary mmap_miss increases
X-Git-Tag: v3.0-rc1~241
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=207d04baa3591a354711e863dd90087fc75873b3;p=pandora-kernel.git

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>
---

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