Re: [PATCH] mm: page_alloc: High-order per-cpu page allocator v3

[Johannes Weiner <hannes@cmpxchg.org>]

On Sun, Nov 27, 2016 at 01:19:54PM +0000, Mel Gorman wrote:
> While it is recognised that this is a mixed bag of results, the patch
> helps a lot more workloads than it hurts and intuitively, avoiding the
> zone->lock in some cases is a good thing.
> 
> Signed-off-by: Mel Gorman <mgorman@techsingularity.net>

This seems like a net gain to me, and the patch loos good too.

Acked-by: Johannes Weiner <hannes@cmpxchg.org>

> @@ -255,6 +255,24 @@ enum zone_watermarks {
>  	NR_WMARK
>  };
>  
> +/*
> + * One per migratetype for order-0 pages and one per high-order up to
> + * and including PAGE_ALLOC_COSTLY_ORDER. This may allow unmovable
> + * allocations to contaminate reclaimable pageblocks if high-order
> + * pages are heavily used.

I think that should be fine. Higher order allocations rely on being
able to compact movable blocks, not on reclaim freeing contiguous
blocks, so poisoning reclaimable blocks is much less of a concern than
poisoning movable blocks. And I'm not aware of any 0 < order < COSTLY
movable allocations that would put movable blocks into an HO cache.

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