linux-kernel - Re: [RFC PATCH v2 0/7] mm: zswap: move writeback LRU from zpool to zswap

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Message-ID: <CAJD7tkbsYxgutGVMjBBeBCviW4UwDwNcM8=xRRwqLxeASHCakg@mail.gmail.com>
Date:   Wed, 7 Jun 2023 02:32:35 -0700
From:   Yosry Ahmed <yosryahmed@...gle.com>
To:     Domenico Cerasuolo <cerasuolodomenico@...il.com>
Cc:     vitaly.wool@...sulko.com, minchan@...nel.org,
        senozhatsky@...omium.org, linux-mm@...ck.org, ddstreet@...e.org,
        sjenning@...hat.com, nphamcs@...il.com, hannes@...xchg.org,
        akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
        kernel-team@...a.com
Subject: Re: [RFC PATCH v2 0/7] mm: zswap: move writeback LRU from zpool to zswap

On Wed, Jun 7, 2023 at 2:24 AM Domenico Cerasuolo
<cerasuolodomenico@...il.com> wrote:
>
> On Wed, Jun 7, 2023 at 11:16 AM Yosry Ahmed <yosryahmed@...gle.com> wrote:
> >
> > On Tue, Jun 6, 2023 at 7:56 AM Domenico Cerasuolo
> > <cerasuolodomenico@...il.com> wrote:
> > >
> > > This series aims to improve the zswap reclaim mechanism by reorganizing
> > > the LRU management. In the current implementation, the LRU is maintained
> > > within each zpool driver, resulting in duplicated code across the three
> > > drivers. The proposed change consists in moving the LRU management from
> > > the individual implementations up to the zswap layer.
> > >
> > > The primary objective of this refactoring effort is to simplify the
> > > codebase. By unifying the reclaim loop and consolidating LRU handling
> > > within zswap, we can eliminate redundant code and improve
> > > maintainability. Additionally, this change enables the reclamation of
> > > stored pages in their actual LRU order. Presently, the zpool drivers
> > > link backing pages in an LRU, causing compressed pages with different
> > > LRU positions to be written back simultaneously.
> > >
> > > The series consists of several patches. The first patch implements the
> > > LRU and the reclaim loop in zswap, but it is not used yet because all
> > > three driver implementations are marked as zpool_evictable.
> > > The following three commits modify each zpool driver to be not
> > > zpool_evictable, allowing the use of the reclaim loop in zswap.
> > > As the drivers removed their shrink functions, the zpool interface is
> > > then trimmed by removing zpool_evictable, zpool_ops, and zpool_shrink.
> > > Finally, the code in zswap is further cleaned up by simplifying the
> > > writeback function and removing the now unnecessary zswap_header.
> > >
> > > Based on mm-stable + commit 399ab221f3ff
> > > ("mm: zswap: shrink until can accept") currently in mm-unstable.
> >
> > I tested this + commit fe1d1f7d0fb5 ("mm: zswap: support exclusive
> > loads") currently in mm-unstable, using zsmalloc and
> > CONFIG_ZSWAP_EXCLUSIVE_LOADS=y. I only ran basic zswap tests with
> > manual writeback induction and made sure everything is sane. I
> > obviously hope you did more involved testing :)
> >
> > The only problem I came across is the conflict with fe1d1f7d0fb5, and
> > I suggested the fix in patch 1. With the fix, everything seems
> > correct.
> >
> > So I guess, FWIW for all the patches except 2 & 3 (for zbud and z3fold):
> > Tested-by: Yosry Ahmed <yosryahmed@...gle.com>
>
> Thanks a lot for the effort! I'll rebase and test it again before submitting the
> new version.

Perhaps give v2 a little bit more time to give other folks a chance to
take a look as well, save yourself (and probably Andrew) the trouble
of sending a new version for every single review :)

>
> >
> > >
> > > V2:
> > > - fixed lru list init/del/del_init (Johannes)
> > > - renamed pool.lock to lru_lock and added lock ordering comment (Yosry)
> > > - trimmed zsmalloc even more (Johannes | Nhat)
> > > - moved ref drop out of writeback function  (Johannes)
> > >
> > > Domenico Cerasuolo (7):
> > >   mm: zswap: add pool shrinking mechanism
> > >   mm: zswap: remove page reclaim logic from zbud
> > >   mm: zswap: remove page reclaim logic from z3fold
> > >   mm: zswap: remove page reclaim logic from zsmalloc
> > >   mm: zswap: remove shrink from zpool interface
> > >   mm: zswap: simplify writeback function
> > >   mm: zswap: remove zswap_header
> > >
> > >  include/linux/zpool.h |  19 +-
> > >  mm/z3fold.c           | 249 +-------------------------
> > >  mm/zbud.c             | 167 +-----------------
> > >  mm/zpool.c            |  48 +----
> > >  mm/zsmalloc.c         | 396 ++----------------------------------------
> > >  mm/zswap.c            | 186 +++++++++++---------
> > >  6 files changed, 130 insertions(+), 935 deletions(-)
> > >
> > > --
> > > 2.34.1
> > >