From: Greg Kroah-Hartman <[email protected]> 3.9-stable review patch. If anyone has any objections, please let me know.
------------------ From: Tomasz Stanislawski <[email protected]> commit 026b08147923142e925a7d0aaa39038055ae0156 upstream. 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. Laura said: We were observing allocation failures of higher order pages (order 5 = 128K typically) under tight memory conditions resulting in driver failure. The output from the page allocation failure showed plenty of free pages of the appropriate order/type/zone and mostly CMA pages in the lower orders. For full disclosure, we still observed some page allocation failures even after applying the patch but the number was drastically reduced and those failures were attributed to fragmentation/other system issues. Signed-off-by: Tomasz Stanislawski <[email protected]> Signed-off-by: Kyungmin Park <[email protected]> Tested-by: Laura Abbott <[email protected]> Cc: Bartlomiej Zolnierkiewicz <[email protected]> Acked-by: Minchan Kim <[email protected]> Cc: Mel Gorman <[email protected]> Tested-by: Marek Szyprowski <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]> Signed-off-by: Greg Kroah-Hartman <[email protected]> --- mm/page_alloc.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -1626,6 +1626,7 @@ static bool __zone_watermark_ok(struct z long min = mark; long lowmem_reserve = z->lowmem_reserve[classzone_idx]; int o; + long free_cma = 0; free_pages -= (1 << order) - 1; if (alloc_flags & ALLOC_HIGH) @@ -1635,9 +1636,10 @@ static bool __zone_watermark_ok(struct z #ifdef CONFIG_CMA /* If allocation can't use CMA areas don't use free CMA pages */ if (!(alloc_flags & ALLOC_CMA)) - free_pages -= zone_page_state(z, NR_FREE_CMA_PAGES); + free_cma = zone_page_state(z, NR_FREE_CMA_PAGES); #endif - if (free_pages <= min + lowmem_reserve) + + if (free_pages - free_cma <= min + lowmem_reserve) return false; for (o = 0; o < order; o++) { /* At the next order, this order's pages become unavailable */ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
