linux-kernel - Re: [PATCH] mm, vmscan: do not count freed pages as PGDEACTIVATE

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Message-ID: <20170114163908.GH26139@cmpxchg.org>
Date:   Sat, 14 Jan 2017 11:39:08 -0500
From:   Johannes Weiner <hannes@...xchg.org>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Hugh Dickins <hughd@...gle.com>, Mel Gorman <mgorman@...e.de>,
        linux-mm@...ck.org, LKML <linux-kernel@...r.kernel.org>,
        Michal Hocko <mhocko@...e.com>
Subject: Re: [PATCH] mm, vmscan: do not count freed pages as PGDEACTIVATE

On Thu, Jan 12, 2017 at 10:12:21PM +0100, Michal Hocko wrote:
> From: Michal Hocko <mhocko@...e.com>
> 
> PGDEACTIVATE represents the number of pages moved from the active list
> to the inactive list. At least this sounds like the original motivation
> of the counter. move_active_pages_to_lru, however, counts pages which
> got freed in the mean time as deactivated as well. This is a very rare
> event and counting them as deactivation in itself is not harmful but it
> makes the code more convoluted than necessary - we have to count both
> all pages and those which are freed which is a bit confusing.
> 
> After this patch the PGDEACTIVATE should have a slightly more clear
> semantic and only count those pages which are moved from the active to
> the inactive list which is a plus.
> 
> Suggested-by: Vlastimil Babka <vbabka@...e.cz>
> Signed-off-by: Michal Hocko <mhocko@...e.com>

I bet it's a small inaccuracy in practice, but now that the trace
patches added a proper counter, might as well consolidate into the
correct one.

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