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From:   Suren Baghdasaryan <surenb@google.com>
Date:   Wed, 24 Nov 2021 14:04:28 -0800
Message-ID: <CAJuCfpGP3ZdeqfYZJ6SUCdnputU-sEOsNYx5Pd9ckL1-zuWC2w@mail.gmail.com>
Subject: Re: [PATCH 1/1] sysctl: change watermark_scale_factor max limit to 30%
To:     Johannes Weiner <hannes@cmpxchg.org>
Cc:     akpm@linux-foundation.org, mhocko@suse.com, mcgrof@kernel.org,
        keescook@chromium.org, yzaikin@google.com,
        dave.hansen@linux.intel.com, vbabka@suse.cz,
        mgorman@techsingularity.net, corbet@lwn.net, yi.zhang@huawei.com,
        xi.fengfei@h3c.com, rppt@kernel.org, linux-doc@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        kernel-team@android.com
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On Wed, Nov 24, 2021 at 1:37 PM Johannes Weiner <hannes@cmpxchg.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@google.com>
>
> Acked-by: Johannes Weiner <hannes@cmpxchg.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.