From 275b12bf5486f6f531111fd3d7dbbf01df427cfe Mon Sep 17 00:00:00 2001
From: Wu Fengguang <fengguang.wu@intel.com>
Date: Tue, 24 May 2011 17:12:28 -0700
Subject: [PATCH] readahead: return early when readahead is disabled
Reduce readahead overheads by returning early in do_sync_mmap_readahead().
tmpfs has ra_pages=0 and it can page fault really fast (not constraint by
IO if not swapping).
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
Tested-by: Tim Chen <tim.c.chen@intel.com>
Reported-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
mm/filemap.c | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)
diff --git a/mm/filemap.c b/mm/filemap.c
index 88354ae0b1fd..c974a2863897 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1556,6 +1556,8 @@ static void do_sync_mmap_readahead(struct vm_area_struct *vma,
/* If we don't want any read-ahead, don't bother */
if (VM_RandomReadHint(vma))
return;
+ if (!ra->ra_pages)
+ return;
if (VM_SequentialReadHint(vma) ||
offset - 1 == (ra->prev_pos >> PAGE_CACHE_SHIFT)) {
@@ -1578,12 +1580,10 @@ static void do_sync_mmap_readahead(struct vm_area_struct *vma,
* mmap read-around
*/
ra_pages = max_sane_readahead(ra->ra_pages);
- if (ra_pages) {
- ra->start = max_t(long, 0, offset - ra_pages/2);
- ra->size = ra_pages;
- ra->async_size = 0;
- ra_submit(ra, mapping, file);
- }
+ ra->start = max_t(long, 0, offset - ra_pages / 2);
+ ra->size = ra_pages;
+ ra->async_size = 0;
+ ra_submit(ra, mapping, file);
}
/*
--
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