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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>
hifive-unleashed-5.1
Wu Fengguang 2011-05-24 17:12:28 -07:00 committed by Linus Torvalds
parent 1495f230fa
commit 275b12bf54
1 changed files with 6 additions and 6 deletions
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12
mm/filemap.c
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@ -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);
}
/*