Re: [PATCH 21/22] mm, compaction: Be selective about what pageblocks to clear skip hints

[Vlastimil Babka]

On 1/18/19 6:51 PM, Mel Gorman wrote:
> Pageblock hints are cleared when compaction restarts or kswapd makes enough
> progress that it can sleep but it's over-eager in that the bit is cleared
> for migration sources with no LRU pages and migration targets with no free
> pages. As pageblock skip hint flushes are relatively rare and out-of-band
> with respect to kswapd, this patch makes a few more expensive checks to
> see if it's appropriate to even clear the bit. Every pageblock that is
> not cleared will avoid 512 pages being scanned unnecessarily on x86-64.
> 
> The impact is variable with different workloads showing small differences
> in latency, success rates and scan rates. This is expected as clearing
> the hints is not that common but doing a small amount of work out-of-band
> to avoid a large amount of work in-band later is generally a good thing.
> 
> Signed-off-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>

Acked-by: Vlastimil Babka <vbabka@xxxxxxx>