linux-kernel - Re: [PATCH 6/8] mm/vmscan: Centralise timeout values for reclaim

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Date:   Thu, 14 Oct 2021 17:38:14 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Mel Gorman <mgorman@...hsingularity.net>,
        Linux-MM <linux-mm@...ck.org>
Cc:     NeilBrown <neilb@...e.de>, Theodore Ts'o <tytso@....edu>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        "Darrick J . Wong" <djwong@...nel.org>,
        Matthew Wilcox <willy@...radead.org>,
        Michal Hocko <mhocko@...e.com>,
        Dave Chinner <david@...morbit.com>,
        Rik van Riel <riel@...riel.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Jonathan Corbet <corbet@....net>,
        Linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 6/8] mm/vmscan: Centralise timeout values for
 reclaim_throttle

On 10/8/21 15:53, Mel Gorman wrote:
> Neil Brown raised concerns about callers of reclaim_throttle specifying
> a timeout value. The original timeout values to congestion_wait() were
> probably pulled out of thin air or copy&pasted from somewhere else.
> This patch centralises the timeout values and selects a timeout based
> on the reason for reclaim throttling. These figures are also pulled
> out of the same thin air but better values may be derived
> 
> Running a workload that is throttling for inappropriate periods
> and tracing mm_vmscan_throttled can be used to pick a more appropriate
> value. Excessive throttling would pick a lower timeout where as
> excessive CPU usage in reclaim context would select a larger timeout.
> Ideally a large value would always be used and the wakeups would
> occur before a timeout but that requires careful testing.
> 
> Signed-off-by: Mel Gorman <mgorman@...hsingularity.net>

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