linux-kernel - Re: [PATCH v2 1/2] free_pcppages_bulk: do not hold lock when picking pages to free

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Date:   Thu, 15 Feb 2018 12:06:08 +0000
From:   Mel Gorman <mgorman@...hsingularity.net>
To:     Aaron Lu <aaron.lu@...el.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Huang Ying <ying.huang@...el.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Kemi Wang <kemi.wang@...el.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Michal Hocko <mhocko@...e.com>,
        Vlastimil Babka <vbabka@...e.cz>
Subject: Re: [PATCH v2 1/2] free_pcppages_bulk: do not hold lock when picking
 pages to free

On Thu, Jan 25, 2018 at 03:21:44PM +0800, Aaron Lu wrote:
> When freeing a batch of pages from Per-CPU-Pages(PCP) back to buddy,
> the zone->lock is held and then pages are chosen from PCP's migratetype
> list. While there is actually no need to do this 'choose part' under
> lock since it's PCP pages, the only CPU that can touch them is us and
> irq is also disabled.
> 
> Moving this part outside could reduce lock held time and improve
> performance. Test with will-it-scale/page_fault1 full load:
> 
> kernel      Broadwell(2S)  Skylake(2S)   Broadwell(4S)  Skylake(4S)
> v4.15-rc4   9037332        8000124       13642741       15728686
> this patch  9608786 +6.3%  8368915 +4.6% 14042169 +2.9% 17433559 +10.8%
> 
> What the test does is: starts $nr_cpu processes and each will repeatedly
> do the following for 5 minutes:
> 1 mmap 128M anonymouse space;
> 2 write access to that space;
> 3 munmap.
> The score is the aggregated iteration.
> 
> https://github.com/antonblanchard/will-it-scale/blob/master/tests/page_fault1.c
> 
> Acked-by: Mel Gorman <mgorman@...hsingularity.net>
> Signed-off-by: Aaron Lu <aaron.lu@...el.com>

It looks like this series may have gotten lost because it was embedded
within an existing thread or else it was the proximity to the merge
window. I suggest a rebase, retest and resubmit unless there was some
major objection that I missed. Patch 1 is fine by me at least. I never
explicitly acked patch 2 but I've no major objection to it, just am a tad
uncomfortable with prefetch magic sauce in general.

-- 
Mel Gorman
SUSE Labs