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From:   Nhat Pham <nphamcs@gmail.com>
Date:   Tue, 21 Nov 2023 17:19:19 -0800
Message-ID: <CAKEwX=NpKqjApRKk2Qp9Hp63xSjRwD-DEu9yX4BvbMd86x2b1g@mail.gmail.com>
Subject: Re: [PATCH v5] zswap: memcontrol: implement zswap writeback disabling
To:     Chris Li <chrisl@kernel.org>
Cc:     Yosry Ahmed <yosryahmed@google.com>,
        Andrew Morton <akpm@linux-foundation.org>, tj@kernel.org,
        lizefan.x@bytedance.com, Johannes Weiner <hannes@cmpxchg.org>,
        Domenico Cerasuolo <cerasuolodomenico@gmail.com>,
        Seth Jennings <sjenning@redhat.com>,
        Dan Streetman <ddstreet@ieee.org>,
        Vitaly Wool <vitaly.wool@konsulko.com>,
        Michal Hocko <mhocko@kernel.org>,
        Roman Gushchin <roman.gushchin@linux.dev>,
        Shakeel Butt <shakeelb@google.com>,
        Muchun Song <muchun.song@linux.dev>,
        Hugh Dickins <hughd@google.com>, corbet@lwn.net,
        Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
        senozhatsky@chromium.org, rppt@kernel.org,
        linux-mm <linux-mm@kvack.org>, kernel-team@meta.com,
        LKML <linux-kernel@vger.kernel.org>, linux-doc@vger.kernel.org,
        david@ixit.cz, Minchan Kim <minchan@google.com>,
        Kairui Song <kasong@tencent.com>,
        Zhongkun He <hezhongkun.hzk@bytedance.com>
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On Tue, Nov 21, 2023 at 11:09=E2=80=AFAM Chris Li <chrisl@kernel.org> wrote=
:
>
> On Tue, Nov 21, 2023 at 10:13=E2=80=AFAM Nhat Pham <nphamcs@gmail.com> wr=
ote:
> >
> > Hi Chris!
> >
> > Thanks for the patch. Would you mind if I spend some time staring
> > at the suggestion again and testing it some more?
>
> Of course, by all means. That is just the minimal version to be
> functional compatible with your zswap.writeback.
>
> I might consider a follow up patch to add "no_zswap" and "none" to
> convert the SSD only swapfile, which can't be expressed by
> zswap.writeback.
> That should cover all 4 combinations of zswap and swap files without
> creating a custom swap tiers list.
>
> "all": zswap + swapfile
> "zswap": zswap only
> "no_zswap": swapfile only.
> "none": no swap.
>
> All keyword names are open to suggestions.

SGTM! There might be some functionality duplication between
memory.swap.tiers =3D no_zswap and memory.zswap.max =3D 0, but
otherwise this seems reasonable to me.

no_zswap sounds a bit awkward, but I can't come up with a better
name.

>
> >
> > If everything is good, I'll squash this patch with the original version=
,
> > (keeping you as a co-developer of the final patch of course), and
> > update the documentation before re-sending everything as v6.
>
> Great!
>
> >
> > Anyway, have a nice Thanksgiving break everyone! Thanks for
> > taking the time to review my patch and discuss the API with me!
>
> My pleasure to discuss the swap with you. We should do the online
> "swap meet" and invite other developers who are interested in the swap
> area as well.

I look forward to this meeting! I'd love to discuss more about (z)swap
development (and more generally, multi-tier memory management).

Generic page promoter/demoter that takes into account workload
(cgroup), access recency (LRU + generations)/frequency, and tier
characteristics (latency, bandwidth, etc.) will be awesome to explore!

>
> Chris