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

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Date:   Mon, 28 Nov 2016 14:54:21 -0500
From:   Johannes Weiner <hannes@...xchg.org>
To:     Mel Gorman <mgorman@...hsingularity.net>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Christoph Lameter <cl@...ux.com>,
        Michal Hocko <mhocko@...e.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Linux-MM <linux-mm@...ck.org>,
        Linux-Kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm: page_alloc: High-order per-cpu page allocator v3

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@...hsingularity.net>

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

Acked-by: Johannes Weiner <hannes@...xchg.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.