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Commit 275b12bf authored by Wu Fengguang's avatar Wu Fengguang Committed by Linus Torvalds
Browse files

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: default avatarWu Fengguang <fengguang.wu@intel.com>
Tested-by: default avatarTim Chen <tim.c.chen@intel.com>
Reported-by: default avatarAndi Kleen <ak@linux.intel.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 1495f230

mm/filemap.c

+6 −6
Original line number Diff line number Diff line
@@ -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)) {
@@ -1578,13 +1580,11 @@ 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);

}

}



/*

 * Asynchronous readahead happens when we find the page and PG_readahead,