linux-kernel - Re: [PATCH 5/3] mm, vmscan: make zone_reclaimable

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Date:	Fri, 29 Jan 2016 19:35:18 +0900
From:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:	mhocko@...nel.org, akpm@...ux-foundation.org
Cc:	torvalds@...ux-foundation.org, hannes@...xchg.org, mgorman@...e.de,
	rientjes@...gle.com, hillf.zj@...baba-inc.com,
	kamezawa.hiroyu@...fujitsu.com, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, mhocko@...e.com
Subject: Re: [PATCH 5/3] mm, vmscan: make zone_reclaimable_pages more precise

Michal Hocko wrote:
> From: Michal Hocko <mhocko@...e.com>
> 
> zone_reclaimable_pages is used in should_reclaim_retry which uses it to
> calculate the target for the watermark check. This means that precise
> numbers are important for the correct decision. zone_reclaimable_pages
> uses zone_page_state which can contain stale data with per-cpu diffs
> not synced yet (the last vmstat_update might have run 1s in the past).
> 
> Use zone_page_state_snapshot in zone_reclaimable_pages instead. None
> of the current callers is in a hot path where getting the precise value
> (which involves per-cpu iteration) would cause an unreasonable overhead.
> 
> Suggested-by: David Rientjes <rientjes@...gle.com>
> Signed-off-by: Michal Hocko <mhocko@...e.com>
> ---
>  mm/vmscan.c | 14 +++++++-------
>  1 file changed, 7 insertions(+), 7 deletions(-)
> 

I didn't know http://lkml.kernel.org/r/20151021130323.GC8805@dhcp22.suse.cz
was forgotten. Anyway,

Acked-by: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>