linux-kernel - Re: [PATCH 1/2] mm/vmscan: Accumulate nr_demoted for accurate demotion statistics

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Message-ID: <Z4EXbSq2Rov78WVF@localhost.localhost>
Date: Fri, 10 Jan 2025 12:49:49 +0000
From: Kaiyang Zhao <kaiyang2@...cmu.edu>
To: Li Zhijian <lizhijian@...itsu.com>
Cc: linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] mm/vmscan: Accumulate nr_demoted for accurate
 demotion statistics

On Fri, Jan 10, 2025 at 08:21:32PM +0800, Li Zhijian wrote:
> In the shrink_folio_list() function, demote_folio_list() can be called
> multiple times, which can lead to inaccurate demotion statistics if the
> number of demoted pages is not accumulated correctly.

It looks like demotion will only be attempted once. On the second pass,
do_demote_pass will be false, demote_folios will be empty and
demote_folio_list() will do nothing. But I guess there is no harm in
making nr_demoted  an accumulation for less confusion in the future...