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Re: [PATCH v2 13/18] mm, compaction: use correct watermark when checking allocation success

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On Tue 31-05-16 15:08:13, Vlastimil Babka wrote:
> The __compact_finished() function uses low watermark in a check that has to
> pass if the direct compaction is to finish and allocation should succeed. This
> is too pessimistic, as the allocation will typically use min watermark. It may
> happen that during compaction, we drop below the low watermark (due to parallel
> activity), but still form the target high-order page. By checking against low
> watermark, we might needlessly continue compaction.
> 
> Similarly, __compaction_suitable() uses low watermark in a check whether
> allocation can succeed without compaction. Again, this is unnecessarily
> pessimistic.
> 
> After this patch, these check will use direct compactor's alloc_flags to
> determine the watermark, which is effectively the min watermark.
> 
> Signed-off-by: Vlastimil Babka <vbabka@suse.cz>

Acked-by: Michal Hocko <mhocko@suse.com>

> ---
>  mm/compaction.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/compaction.c b/mm/compaction.c
> index a399e7ca4630..4b21a26694a2 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -1262,7 +1262,7 @@ static enum compact_result __compact_finished(struct zone *zone, struct compact_
>  		return COMPACT_CONTINUE;
>  
>  	/* Compaction run is not finished if the watermark is not met */
> -	watermark = low_wmark_pages(zone);
> +	watermark = zone->watermark[cc->alloc_flags & ALLOC_WMARK_MASK];
>  
>  	if (!zone_watermark_ok(zone, cc->order, watermark, cc->classzone_idx,
>  							cc->alloc_flags))
> @@ -1327,7 +1327,7 @@ static enum compact_result __compaction_suitable(struct zone *zone, int order,
>  	if (is_via_compact_memory(order))
>  		return COMPACT_CONTINUE;
>  
> -	watermark = low_wmark_pages(zone);
> +	watermark = zone->watermark[alloc_flags & ALLOC_WMARK_MASK];
>  	/*
>  	 * If watermarks for high-order allocation are already met, there
>  	 * should be no need for compaction at all.
> @@ -1341,7 +1341,7 @@ static enum compact_result __compaction_suitable(struct zone *zone, int order,
>  	 * This is because during migration, copies of pages need to be
>  	 * allocated and for a short time, the footprint is higher
>  	 */
> -	watermark += (2UL << order);
> +	watermark = low_wmark_pages(zone) + (2UL << order);
>  	if (!__zone_watermark_ok(zone, 0, watermark, classzone_idx,
>  				 alloc_flags, wmark_target))
>  		return COMPACT_SKIPPED;
> -- 
> 2.8.3

-- 
Michal Hocko
SUSE Labs

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[PATCH v2 00/18] make direct compaction more deterministic Vlastimil Babka <vbabka@suse.cz> - 2016-05-31 15:10 +0200
  [PATCH v2 02/18] mm, page_alloc: set alloc_flags only once in slowpath Vlastimil Babka <vbabka@suse.cz> - 2016-05-31 15:10 +0200
  [PATCH v2 15/18] mm, compaction: use proper alloc_flags in __compaction_suitable() Vlastimil Babka <vbabka@suse.cz> - 2016-05-31 15:10 +0200
  [PATCH v2 14/18] mm, compaction: create compact_gap wrapper Vlastimil Babka <vbabka@suse.cz> - 2016-05-31 15:10 +0200
    Re: [PATCH v2 14/18] mm, compaction: create compact_gap wrapper Michal Hocko <mhocko@kernel.org> - 2016-06-01 16:10 +0200
  [PATCH v2 17/18] mm, vmscan: make compaction_ready() more accurate and readable Vlastimil Babka <vbabka@suse.cz> - 2016-05-31 15:10 +0200
    Re: [PATCH v2 17/18] mm, vmscan: make compaction_ready() more  accurate and readable Michal Hocko <mhocko@kernel.org> - 2016-06-01 16:20 +0200
  [PATCH v2 04/18] mm, page_alloc: restructure direct compaction handling in slowpath Vlastimil Babka <vbabka@suse.cz> - 2016-05-31 15:20 +0200
  [PATCH v2 03/18] mm, page_alloc: don't retry initial attempt in slowpath Vlastimil Babka <vbabka@suse.cz> - 2016-05-31 15:20 +0200
    Re: [PATCH v2 03/18] mm, page_alloc: don't retry initial attempt in  slowpath Michal Hocko <mhocko@kernel.org> - 2016-06-01 15:30 +0200
      Re: [PATCH v2 03/18] mm, page_alloc: don't retry initial attempt in  slowpath Vlastimil Babka <vbabka@suse.cz> - 2016-06-01 17:00 +0200
  [PATCH v2 05/18] mm, page_alloc: make THP-specific decisions more generic Vlastimil Babka <vbabka@suse.cz> - 2016-05-31 15:20 +0200
  [PATCH v2 13/18] mm, compaction: use correct watermark when checking allocation success Vlastimil Babka <vbabka@suse.cz> - 2016-05-31 15:20 +0200
    Re: [PATCH v2 13/18] mm, compaction: use correct watermark when  checking allocation success Michal Hocko <mhocko@kernel.org> - 2016-06-01 16:00 +0200
  [PATCH v2 06/18] mm, thp: remove __GFP_NORETRY from khugepaged and madvised allocations Vlastimil Babka <vbabka@suse.cz> - 2016-05-31 15:20 +0200
    Re: [PATCH v2 06/18] mm, thp: remove __GFP_NORETRY from khugepaged  and madvised allocations Michal Hocko <mhocko@kernel.org> - 2016-06-01 15:40 +0200
  [PATCH v2 12/18] mm, compaction: more reliably increase direct compaction priority Vlastimil Babka <vbabka@suse.cz> - 2016-05-31 15:20 +0200
    Re: [PATCH v2 12/18] mm, compaction: more reliably increase direct  compaction priority Michal Hocko <mhocko@kernel.org> - 2016-06-01 16:00 +0200
  [PATCH v2 11/18] mm, compaction: add the ultimate direct compaction priority Vlastimil Babka <vbabka@suse.cz> - 2016-05-31 15:20 +0200
  [PATCH v2 10/18] mm, compaction: cleanup unused functions Vlastimil Babka <vbabka@suse.cz> - 2016-05-31 15:20 +0200
    Re: [PATCH v2 10/18] mm, compaction: cleanup unused functions Michal Hocko <mhocko@kernel.org> - 2016-06-01 15:50 +0200
  [PATCH v2 01/18] mm, compaction: don't isolate PageWriteback pages in MIGRATE_SYNC_LIGHT mode Vlastimil Babka <vbabka@suse.cz> - 2016-05-31 15:20 +0200
  [PATCH v2 09/18] mm, compaction: make whole_zone flag ignore cached scanner positions Vlastimil Babka <vbabka@suse.cz> - 2016-05-31 15:20 +0200
  [PATCH v2 18/18] mm, vmscan: use proper classzone_idx in should_continue_reclaim() Vlastimil Babka <vbabka@suse.cz> - 2016-05-31 15:20 +0200
    Re: [PATCH v2 18/18] mm, vmscan: use proper classzone_idx in  should_continue_reclaim() Michal Hocko <mhocko@kernel.org> - 2016-06-01 16:30 +0200
      Re: [PATCH v2 18/18] mm, vmscan: use proper classzone_idx in  should_continue_reclaim() Vlastimil Babka <vbabka@suse.cz> - 2016-06-01 17:20 +0200
        Re: [PATCH v2 18/18] mm, vmscan: use proper classzone_idx in  should_continue_reclaim() Michal Hocko <mhocko@kernel.org> - 2016-06-01 17:50 +0200
  [PATCH v2 08/18] mm, compaction: simplify contended compaction handling Vlastimil Babka <vbabka@suse.cz> - 2016-05-31 15:20 +0200
  [PATCH v2 16/18] mm, compaction: require only min watermarks for non-costly orders Vlastimil Babka <vbabka@suse.cz> - 2016-05-31 15:20 +0200
    Re: [PATCH v2 16/18] mm, compaction: require only min watermarks for  non-costly orders Michal Hocko <mhocko@kernel.org> - 2016-06-01 16:10 +0200
  [PATCH v2 07/18] mm, compaction: introduce direct compaction priority Vlastimil Babka <vbabka@suse.cz> - 2016-05-31 15:20 +0200

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