[10/25] mm, compaction: Ignore the fragmentation avoidance boost for isolation and compaction
diff mbox series

Message ID 20190104125011.16071-11-mgorman@techsingularity.net
State New
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Series
  • Increase success rates and reduce latency of compaction v2
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Commit Message

Mel Gorman Jan. 4, 2019, 12:49 p.m. UTC
When pageblocks get fragmented, watermarks are artifically boosted to
reclaim pages to avoid further fragmentation events. However, compaction
is often either fragmentation-neutral or moving movable pages away from
unmovable/reclaimable pages. As the true watermarks are preserved, allow
compaction to ignore the boost factor.

The expected impact is very slight as the main benefit is that compaction
is slightly more likely to succeed when the system has been fragmented
very recently. On both 1-socket and 2-socket machines for THP-intensive
allocation during fragmentation the success rate was increased by less
than 1% which is marginal. However, detailed tracing indicated that
failure of migration due to a premature ENOMEM triggered by watermark
checks were eliminated.

Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
---
 mm/page_alloc.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Comments

Vlastimil Babka Jan. 15, 2019, 1:18 p.m. UTC | #1
On 1/4/19 1:49 PM, Mel Gorman wrote:
> When pageblocks get fragmented, watermarks are artifically boosted to
> reclaim pages to avoid further fragmentation events. However, compaction
> is often either fragmentation-neutral or moving movable pages away from
> unmovable/reclaimable pages. As the true watermarks are preserved, allow
> compaction to ignore the boost factor.
> 
> The expected impact is very slight as the main benefit is that compaction
> is slightly more likely to succeed when the system has been fragmented
> very recently. On both 1-socket and 2-socket machines for THP-intensive
> allocation during fragmentation the success rate was increased by less
> than 1% which is marginal. However, detailed tracing indicated that
> failure of migration due to a premature ENOMEM triggered by watermark
> checks were eliminated.
> 
> Signed-off-by: Mel Gorman <mgorman@techsingularity.net>

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

> ---
>  mm/page_alloc.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 57ba9d1da519..05c9a81d54ed 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -2958,7 +2958,7 @@ int __isolate_free_page(struct page *page, unsigned int order)
>  		 * watermark, because we already know our high-order page
>  		 * exists.
>  		 */
> -		watermark = min_wmark_pages(zone) + (1UL << order);
> +		watermark = zone->_watermark[WMARK_MIN] + (1UL << order);
>  		if (!zone_watermark_ok(zone, 0, watermark, 0, ALLOC_CMA))
>  			return 0;
>  
>

Patch
diff mbox series

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 57ba9d1da519..05c9a81d54ed 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2958,7 +2958,7 @@  int __isolate_free_page(struct page *page, unsigned int order)
 		 * watermark, because we already know our high-order page
 		 * exists.
 		 */
-		watermark = min_wmark_pages(zone) + (1UL << order);
+		watermark = zone->_watermark[WMARK_MIN] + (1UL << order);
 		if (!zone_watermark_ok(zone, 0, watermark, 0, ALLOC_CMA))
 			return 0;