linux-kernel - Re: [PATCH v6] zswap: memcontrol: implement zswap writeback disabling

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Message-ID: <CAF8kJuNzFcBRW=2CbgG=seA=CNgyzD8DNXNY02uy0HUsLbg9JQ@mail.gmail.com>
Date:   Tue, 12 Dec 2023 15:57:51 -0800
From:   Chris Li <chrisl@...nel.org>
To:     Minchan Kim <minchan@...nel.org>
Cc:     Johannes Weiner <hannes@...xchg.org>,
        Nhat Pham <nphamcs@...il.com>, akpm@...ux-foundation.org,
        tj@...nel.org, lizefan.x@...edance.com,
        cerasuolodomenico@...il.com, yosryahmed@...gle.com,
        sjenning@...hat.com, ddstreet@...e.org, vitaly.wool@...sulko.com,
        mhocko@...nel.org, roman.gushchin@...ux.dev, shakeelb@...gle.com,
        muchun.song@...ux.dev, hughd@...gle.com, corbet@....net,
        konrad.wilk@...cle.com, senozhatsky@...omium.org, rppt@...nel.org,
        linux-mm@...ck.org, kernel-team@...a.com,
        linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
        david@...t.cz, Kairui Song <kasong@...cent.com>,
        Zhongkun He <hezhongkun.hzk@...edance.com>
Subject: Re: [PATCH v6] zswap: memcontrol: implement zswap writeback disabling

Hi Minchan,

On Mon, Dec 11, 2023 at 2:55 PM Minchan Kim <minchan@...nel.org> wrote:

> > > 3) Android has some fancy swap ideas led by those patches.
> > > https://lore.kernel.org/linux-mm/20230710221659.2473460-1-minchan@kernel.org/
> > > It got shot down due to removal of frontswap. But the usage case and
> > > product requirement is there.
> > > +Minchan
> >
> > This looks like an optimization for zram to bypass the block layer and
> > hook directly into the swap code. Correct me if I'm wrong, but this
> > doesn't appear to have anything to do with per-cgroup backend control.
>
> Hi Johannes,
>
> I haven't been following the thread closely, but I noticed the discussion
> about potential use cases for zram with memcg.
>
> One interesting idea I have is to implement a swap controller per cgroup.
> This would allow us to tailor the zram swap behavior to the specific needs of
> different groups.
>
> For example, Group A, which is sensitive to swap latency, could use zram swap
> with a fast compression setting, even if it sacrifices some compression ratio.
> This would prioritize quick access to swapped data, even if it takes up more space.
>
> On the other hand, Group B, which can tolerate higher swap latency, could benefit
> from a slower compression setting that achieves a higher compression ratio.
> This would maximize memory efficiency at the cost of slightly slower data access.

That is a very solid usage case. Thanks for sharing this swap backend
usage story. It goes beyond my original memory.swap.teires idea as
well.

We can have some zram specific knobs to control what compression
setting is using. Moving data between different compression settings
would be an interesting topic. It might fit the swap.tiers usage model
as well. I am just thinking it out loud. Maybe define different
compression settings as different tiers and then allow the cgroup to
enroll into one of the tiers list.

>
> This approach could provide a more nuanced and flexible way to manage swap usage
> within different cgroups.
>

That is again very wonderful insight.

Thanks

Chris