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SubjectRe: [PATCH v2 3/4] mm: try to exhaust highatomic reserve before the OOM
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On 10/12/2016 07:33 AM, Minchan Kim wrote:
> It's weird to show that zone has enough free memory above min
> watermark but OOMed with 4K GFP_KERNEL allocation due to
> reserved highatomic pages. As last resort, try to unreserve
> highatomic pages again and if it has moved pages to
> non-highatmoc free list, retry reclaim once more.

I would move the details (OOM report etc) from the cover letter here, otherwise
they end up in Patch 1's changelog, which is less helpful.

> Signed-off-by: Michal Hocko <mhocko@suse.com>
> Signed-off-by: Minchan Kim <minchan@kernel.org>

Acked-by: Vlastimil Babka <vbabka@suse.cz>

> ---
> mm/page_alloc.c | 15 +++++++++++----
> 1 file changed, 11 insertions(+), 4 deletions(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 18808f392718..a7472426663f 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -2080,7 +2080,7 @@ static void reserve_highatomic_pageblock(struct page *page, struct zone *zone,
> * intense memory pressure but failed atomic allocations should be easier
> * to recover from than an OOM.
> */
> -static void unreserve_highatomic_pageblock(const struct alloc_context *ac)
> +static bool unreserve_highatomic_pageblock(const struct alloc_context *ac)
> {
> struct zonelist *zonelist = ac->zonelist;
> unsigned long flags;
> @@ -2088,6 +2088,7 @@ static void unreserve_highatomic_pageblock(const struct alloc_context *ac)
> struct zone *zone;
> struct page *page;
> int order;
> + bool ret = false;
>
> for_each_zone_zonelist_nodemask(zone, z, zonelist, ac->high_zoneidx,
> ac->nodemask) {
> @@ -2136,12 +2137,14 @@ static void unreserve_highatomic_pageblock(const struct alloc_context *ac)
> * may increase.
> */
> set_pageblock_migratetype(page, ac->migratetype);
> - move_freepages_block(zone, page, ac->migratetype);
> + ret = move_freepages_block(zone, page, ac->migratetype);
> spin_unlock_irqrestore(&zone->lock, flags);
> - return;
> + return ret;
> }
> spin_unlock_irqrestore(&zone->lock, flags);
> }
> +
> + return ret;
> }
>
> /* Remove an element from the buddy allocator from the fallback list */
> @@ -3457,8 +3460,12 @@ should_reclaim_retry(gfp_t gfp_mask, unsigned order,
> * Make sure we converge to OOM if we cannot make any progress
> * several times in the row.
> */
> - if (*no_progress_loops > MAX_RECLAIM_RETRIES)
> + if (*no_progress_loops > MAX_RECLAIM_RETRIES) {
> + /* Before OOM, exhaust highatomic_reserve */
> + if (unreserve_highatomic_pageblock(ac))
> + return true;
> return false;
> + }
>
> /*
> * Keep reclaiming pages while there is a chance this will lead
>

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