linux-kernel - Re: [PATCH] mm: Stop kswapd early when nothing's waiting for it to free pages

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Message-ID: <20200219224231.GA5190@sultan-book.localdomain>
Date:   Wed, 19 Feb 2020 14:42:31 -0800
From:   Sultan Alsawaf <sultan@...neltoast.com>
To:     Mel Gorman <mgorman@...e.de>
Cc:     Michal Hocko <mhocko@...nel.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Johannes Weiner <hannes@...xchg.org>
Subject: Re: [PATCH] mm: Stop kswapd early when nothing's waiting for it to
 free pages

On Wed, Feb 19, 2020 at 09:45:13PM +0000, Mel Gorman wrote:
> This could be watermark boosting run wild again. Can you test with
> sysctl vm.watermark_boost_factor=0 or the following patch? (preferably
> both to compare and contrast).

I can test that, but something to note is that I've been doing equal testing
with this on 4.4, which exhibits the same behavior, and that kernel doesn't have
watermark boosting in it, as far as I can tell.

I don't think what we're addressing here is a "bug", but rather something
fundamental about how we've been thinking about kswapd lifetime. The argument
here is that it's not coherent to be letting kswapd run as it does, and instead
gating it on outstanding allocation requests provides much more reasonable
behavior, given real workloads and use patterns.

Does that make sense and seem reasonable?

Sultan