linux-kernel - Re: [PATCH 27/27] mm: vmstat: Account per-zone stalls and pages skipped during reclaim

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Message-ID: <a72ece1f-e481-f1cd-7072-e7d021754094@suse.cz>
Date:	Fri, 17 Jun 2016 14:39:46 +0200
From:	Vlastimil Babka <vbabka@...e.cz>
To:	Mel Gorman <mgorman@...hsingularity.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux-MM <linux-mm@...ck.org>
Cc:	Rik van Riel <riel@...riel.com>,
	Johannes Weiner <hannes@...xchg.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 27/27] mm: vmstat: Account per-zone stalls and pages
 skipped during reclaim

On 06/09/2016 08:04 PM, Mel Gorman wrote:
> The vmstat allocstall was fairly useful in the general sense but
> node-based LRUs change that. It's important to know if a stall was for an
> address-limited allocation request as this will require skipping pages from
> other zones. This patch adds pgstall_* counters to replace allocstall. The
> sum of the counters will equal the old allocstall so it can be trivially
> recalculated. A high number of address-limited allocation requests may
> result in a lot of useless LRU scanning for suitable pages.
>
> As address-limited allocations require pages to be skipped, it's important
> to know how much useless LRU scanning took place so this patch adds
> pgskip* counters. This yields the following model
>
> 1. The number of address-space limited stalls can be accounted for (pgstall)
> 2. The amount of useless work required to reclaim the data is accounted (pgskip)
> 3. The total number of scans is available from pgscan_kswapd and pgscan_direct
>    so from that the ratio of useful to useless scans can be calculated.
>
> Signed-off-by: Mel Gorman <mgorman@...hsingularity.net>

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

Nice work!