linux-kernel - Re: [PATCH] mm: madvise: fix uneven accounting of psi

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Message-ID: <70743150-dc85-1a1a-87ec-e3dd9f72c5d0@quicinc.com>
Date:   Mon, 26 Jun 2023 20:01:23 +0530
From:   Charan Teja Kalla <quic_charante@...cinc.com>
To:     Suren Baghdasaryan <surenb@...gle.com>
CC:     Johannes Weiner <hannes@...xchg.org>, <akpm@...ux-foundation.org>,
        <minchan@...nel.org>, <quic_pkondeti@...cinc.com>,
        <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm: madvise: fix uneven accounting of psi

Hi Suren,

On 6/10/2023 4:43 AM, Suren Baghdasaryan wrote:
>>> I can see use for that from userspace to detect incorrect madvise()
>>> and adjust its aggressiveness. I think the API might get a bit complex
>>> because of the need to associate refaults with specific madvise()/VMAs
>>> to understand which hint was incorrect and adjust the behavior.
>>> Instead what is the opinion about giving an MADV_PAGEOUT_INACTIVE
>> interface which does operate on a page only If it is on the inactive
>> list and !PageWorkingset ?
> IOW you want a less aggressive mechanism which can be used by the
> userspace to tell the kernel "I think these pages won't be used but
> I'm not 100% sure, so drop them only if they are inactive"?
>  I don't know how much that will help when the madvise() ends up being
> wrong but maybe you can quickly experiment and tell us if the
> difference is substantial?

We did some extensive testing on Android and this ask is not helping us
much. I am really not sure if there is some other usecase that can
benefit from this. So, for now I just stick to your suggestion of making
the pages on the Active list as the Workingset at the time of pageout.
>

Thanks.