Re: [PATCH v2 3/4] mm: try to exhaust highatomic reserve before the OOM

[Vlastimil Babka]

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@xxxxxxxx>
> Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>

Acked-by: Vlastimil Babka <vbabka@xxxxxxx>

> ---
>  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