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From: Chris Li <chrisl@kernel.org>
Date: Tue, 6 Feb 2024 21:52:54 -0800
Message-ID: <CAF8kJuN=yN-fgv3RgQYq2kEbsUr5=bD1fbWVE5QNRTGAO9JgJg@mail.gmail.com>
Subject: Re: [PATCH v3] mm/zswap: invalidate old entry when store fail or !zswap_enabled
To: Yosry Ahmed <yosryahmed@google.com>
Cc: chengming.zhou@linux.dev, hannes@cmpxchg.org, nphamcs@gmail.com, 
	akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, 
	Chengming Zhou <zhouchengming@bytedance.com>, stable@vger.kernel.org
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On Tue, Feb 6, 2024 at 9:46=E2=80=AFPM Yosry Ahmed <yosryahmed@google.com> =
wrote:
>
> > > @@ -1608,14 +1598,12 @@ bool zswap_store(struct folio *folio)
> > >         /* map */
> > >         spin_lock(&tree->lock);
> > >         /*
> > > -        * A duplicate entry should have been removed at the beginnin=
g of this
> > > -        * function. Since the swap entry should be pinned, if a dupl=
icate is
> > > -        * found again here it means that something went wrong in the=
 swap
> > > -        * cache.
> > > +        * The folio may have been dirtied again, invalidate the
> > > +        * possibly stale entry before inserting the new entry.
> > >          */
> > > -       while (zswap_rb_insert(&tree->rbroot, entry, &dupentry) =3D=
=3D -EEXIST) {
> > > -               WARN_ON(1);
> > > +       if (zswap_rb_insert(&tree->rbroot, entry, &dupentry) =3D=3D -=
EEXIST) {
> > >                 zswap_invalidate_entry(tree, dupentry);
> > > +               VM_WARN_ON(zswap_rb_insert(&tree->rbroot, entry, &dup=
entry));
> >
> > It seems there is only one path called zswap_rb_insert() and there is
> > no loop to repeat the insert any more. Can we have the
> > zswap_rb_insert() install the entry and return the dupentry? We can
> > still just call zswap_invalidate_entry() on the duplicate. The mapping
> > of the dupentry has been removed when  zswap_rb_insert() returns. That
> > will save a repeat lookup on the duplicate case.
> > After this change, the zswap_rb_insert() will map to the xarray
> > xa_store() pretty nicely.
>
> I brought this up in v1 [1]. We agreed to leave it as-is for now since
> we expect the xarray conversion soon-ish. No need to update
> zswap_rb_insert() only to replace it with xa_store() later anyway.
>
> [1] https://lore.kernel.org/lkml/ZcFne336KJdbrvvS@google.com/
>
Ah, thanks for the pointer. I miss your earlier reply.

Acked-by: Chris Li <chrisl@kernel.org>

Chris