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Subject: Re: [PATCH 4/6] mm/page_alloc: Scale the number of pages that are
 batch freed
To:     Mel Gorman <mgorman@techsingularity.net>,
        Andrew Morton <akpm@linux-foundation.org>
Cc:     Hillf Danton <hdanton@sina.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Michal Hocko <mhocko@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Linux-MM <linux-mm@kvack.org>
References: <20210525080119.5455-1-mgorman@techsingularity.net>
 <20210525080119.5455-5-mgorman@techsingularity.net>
From:   Vlastimil Babka <vbabka@suse.cz>
Message-ID: <c7e5a4e7-43df-0f49-d297-1b4621221ca1@suse.cz>
Date:   Fri, 28 May 2021 13:19:45 +0200
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On 5/25/21 10:01 AM, Mel Gorman wrote:
> When a task is freeing a large number of order-0 pages, it may acquire
> the zone->lock multiple times freeing pages in batches. This may
> unnecessarily contend on the zone lock when freeing very large number
> of pages. This patch adapts the size of the batch based on the recent
> pattern to scale the batch size for subsequent frees.
> 
> As the machines I used were not large enough to test this are not large
> enough to illustrate a problem, a debugging patch shows patterns like
> the following (slightly editted for clarity)
> 
> Baseline vanilla kernel
>   time-unmap-14426   [...] free_pcppages_bulk: free   63 count  378 high  378
>   time-unmap-14426   [...] free_pcppages_bulk: free   63 count  378 high  378
>   time-unmap-14426   [...] free_pcppages_bulk: free   63 count  378 high  378
>   time-unmap-14426   [...] free_pcppages_bulk: free   63 count  378 high  378
>   time-unmap-14426   [...] free_pcppages_bulk: free   63 count  378 high  378
> 
> With patches
>   time-unmap-7724    [...] free_pcppages_bulk: free  126 count  814 high  814
>   time-unmap-7724    [...] free_pcppages_bulk: free  252 count  814 high  814
>   time-unmap-7724    [...] free_pcppages_bulk: free  504 count  814 high  814
>   time-unmap-7724    [...] free_pcppages_bulk: free  751 count  814 high  814
>   time-unmap-7724    [...] free_pcppages_bulk: free  751 count  814 high  814
> 
> Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
> Acked-by: Dave Hansen <dave.hansen@linux.intel.com>

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