tree 8766e607dfe8983d293741f1392c9b6ee2962251
parent 1bf76b117b96667b906976c757ed2a5f6342246c
author Tomasz Stanislawski <t.stanislaws@samsung.com> 1368085846 +0200
committer Laura Abbott <lauraa@codeaurora.org> 1368669878 -0700

mm: page_alloc: fix watermark check in __zone_watermark_ok()

The watermark check consists of two sub-checks.
The first one is:

	if (free_pages <= min + lowmem_reserve)
		return false;

The check assures that there is minimal amount of RAM in the zone.  If CMA is
used then the free_pages is reduced by the number of free pages in CMA prior
to the over-mentioned check.

	if (!(alloc_flags & ALLOC_CMA))
		free_pages -= zone_page_state(z, NR_FREE_CMA_PAGES);

This prevents the zone from being drained from pages available for non-movable
allocations.

The second check prevents the zone from getting too fragmented.

	for (o = 0; o < order; o++) {
		free_pages -= z->free_area[o].nr_free << o;
		min >>= 1;
		if (free_pages <= min)
			return false;
	}

The field z->free_area[o].nr_free is equal to the number of free pages
including free CMA pages.  Therefore the CMA pages are subtracted twice.  This
may cause a false positive fail of __zone_watermark_ok() if the CMA area gets
strongly fragmented.  In such a case there are many 0-order free pages located
in CMA. Those pages are subtracted twice therefore they will quickly drain
free_pages during the check against fragmentation.  The test fails even though
there are many free non-cma pages in the zone.

This patch fixes this issue by subtracting CMA pages only for a purpose of
(free_pages <= min + lowmem_reserve) check.

Change-Id: I899919476cfca4bfa48bb5877ed6644784a43ce0
Signed-off-by: Tomasz Stanislawski <t.stanislaws@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Patch-mainline: linux-mm @ 05/09/2013, 12:50AM
Signed-off-by: Laura Abbott <lauraa@codeaurora.org>