From: Minchan Kim <minchan@xxxxxxxxxx> Subject: mm: make unreserve highatomic functions reliable Currently, unreserve_highatomic_pageblock bails out if it found highatomic pageblock regardless of really moving free pages from the one so that it could mitigate unreserve logic's goal which saves OOM of a process. This patch makes unreserve functions bail out only if it moves some pages out of !highatomic free list to avoid such false positive. Another potential problem is that by race between page freeing and reserve highatomic function, pages could be in highatomic free list even though the pageblock is !high atomic migratetype. In that case, unreserve_highatomic_pageblock can be void if count of highatomic reserve is less than pageblock_nr_pages. We could solve it simply via draining all of reserved pages before the OOM. It would have a safeguard role to exhuast reserved pages before converging to OOM. Link: http://lkml.kernel.org/r/1476259429-18279-5-git-send-email-minchan@xxxxxxxxxx Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx> Signed-off-by: Michal Hocko <mhocko@xxxxxxxx> Acked-by: Vlastimil Babka <vbabka@xxxxxxx> Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx> Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> Cc: Sangseok Lee <sangseok.lee@xxxxxxx> Cc: Michal Hocko <mhocko@xxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/page_alloc.c | 24 +++++++++++++++++------- 1 file changed, 17 insertions(+), 7 deletions(-) diff -puN mm/page_alloc.c~mm-make-unreserve-highatomic-functions-reliable mm/page_alloc.c --- a/mm/page_alloc.c~mm-make-unreserve-highatomic-functions-reliable +++ a/mm/page_alloc.c @@ -2058,8 +2058,12 @@ out_unlock: * potentially hurts the reliability of high-order allocations when under * intense memory pressure but failed atomic allocations should be easier * to recover from than an OOM. + * + * If @force is true, try to unreserve a pageblock even though highatomic + * pageblock is exhausted. */ -static bool unreserve_highatomic_pageblock(const struct alloc_context *ac) +static bool unreserve_highatomic_pageblock(const struct alloc_context *ac, + bool force) { struct zonelist *zonelist = ac->zonelist; unsigned long flags; @@ -2071,8 +2075,12 @@ static bool unreserve_highatomic_pageblo for_each_zone_zonelist_nodemask(zone, z, zonelist, ac->high_zoneidx, ac->nodemask) { - /* Preserve at least one pageblock */ - if (zone->nr_reserved_highatomic <= pageblock_nr_pages) + /* + * Preserve at least one pageblock unless memory pressure + * is really high. + */ + if (!force && zone->nr_reserved_highatomic <= + pageblock_nr_pages) continue; spin_lock_irqsave(&zone->lock, flags); @@ -2117,8 +2125,10 @@ static bool unreserve_highatomic_pageblo */ set_pageblock_migratetype(page, ac->migratetype); ret = move_freepages_block(zone, page, ac->migratetype); - spin_unlock_irqrestore(&zone->lock, flags); - return ret; + if (ret) { + spin_unlock_irqrestore(&zone->lock, flags); + return ret; + } } spin_unlock_irqrestore(&zone->lock, flags); } @@ -3322,7 +3332,7 @@ retry: * Shrink them them and try again */ if (!page && !drained) { - unreserve_highatomic_pageblock(ac); + unreserve_highatomic_pageblock(ac, false); drain_all_pages(NULL); drained = true; goto retry; @@ -3441,7 +3451,7 @@ should_reclaim_retry(gfp_t gfp_mask, uns */ if (*no_progress_loops > MAX_RECLAIM_RETRIES) { /* Before OOM, exhaust highatomic_reserve */ - return unreserve_highatomic_pageblock(ac); + return unreserve_highatomic_pageblock(ac, true); } /* _ -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
