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).
Tested-by: Tim Chen <tim.c.chen@xxxxxxxxx>
Reported-by: Andi Kleen <ak@xxxxxxxxxxxxxxx>
Signed-off-by: Wu Fengguang <fengguang.wu@xxxxxxxxx>
---
mm/filemap.c | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)
--- linux-next.orig/mm/filemap.c 2011-04-23 08:56:59.000000000 +0800
+++ linux-next/mm/filemap.c 2011-04-23 09:01:44.000000000 +0800
@@ -1528,6 +1528,8 @@ static void do_sync_mmap_readahead(struc
/* 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)) {
@@ -1550,12 +1552,10 @@ static void do_sync_mmap_readahead(struc
* 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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