linux-kernel - Re: [PATCH 1/1] sysctl: change watermark_scale

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Date:   Wed, 24 Nov 2021 14:04:28 -0800
From:   Suren Baghdasaryan <surenb@...gle.com>
To:     Johannes Weiner <hannes@...xchg.org>
Cc:     akpm@...ux-foundation.org, mhocko@...e.com, mcgrof@...nel.org,
        keescook@...omium.org, yzaikin@...gle.com,
        dave.hansen@...ux.intel.com, vbabka@...e.cz,
        mgorman@...hsingularity.net, corbet@....net, yi.zhang@...wei.com,
        xi.fengfei@....com, rppt@...nel.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        kernel-team@...roid.com
Subject: Re: [PATCH 1/1] sysctl: change watermark_scale_factor max limit to 30%

On Wed, Nov 24, 2021 at 1:37 PM Johannes Weiner <hannes@...xchg.org> wrote:
>
> On Wed, Nov 24, 2021 at 11:36:04AM -0800, Suren Baghdasaryan wrote:
> > For embedded systems with low total memory, having to run applications
> > with relatively large memory requirements, 10% max limitation for
> > watermark_scale_factor poses an issue of triggering direct reclaim
> > every time such application is started. This results in slow application
> > startup times and bad end-user experience.
> > By increasing watermark_scale_factor max limit we allow vendors more
> > flexibility to choose the right level of kswapd aggressiveness for
> > their device and workload requirements.
> >
> > Signed-off-by: Suren Baghdasaryan <surenb@...gle.com>
>
> Acked-by: Johannes Weiner <hannes@...xchg.org>

Thanks!

>
> No objection from me as this limit was always totally arbitrary. But I
> have to say I'm a bit surprised: The current maximum setting will wake
> kswapd when free memory drops below 10% and have it reclaim until
> 20%. This seems like quite a lot? Are there applications that really
> want kswapd to wake at 30% and target 60% of memory free?

The example I was given by a vendor was Camera application requiring
0.25G on 1GB device. Camera apps are notoriously memory hungry on
Android and on low-memory devices it can require more than 20% of
total memory to run.