linux-kernel - Re: [PATCH v9] zswap: replace RB tree with xarray

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Date: Tue, 26 Mar 2024 14:04:01 -0700
From: Nhat Pham <nphamcs@...il.com>
To: Chris Li <chrisl@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>, linux-kernel@...r.kernel.org, 
	linux-mm@...ck.org, Yosry Ahmed <yosryahmed@...gle.com>, 
	Johannes Weiner <hannes@...xchg.org>, "Matthew Wilcox (Oracle)" <willy@...radead.org>, 
	Chengming Zhou <zhouchengming@...edance.com>, Barry Song <v-songbaohua@...o.com>
Subject: Re: [PATCH v9] zswap: replace RB tree with xarray

On Tue, Mar 26, 2024 at 11:42 AM Chris Li <chrisl@...nel.org> wrote:
>
> > -        * When reading into the swapcache, invalidate our entry. The
> > +        * When reading into the swapcache, erase our entry. The
> >          * swapcache can be the authoritative owner of the page and
> >          * its mappings, and the pressure that results from having two
> >          * in-memory copies outweighs any benefits of caching the
> > @@ -1649,8 +1581,12 @@ bool zswap_load(struct folio *folio)
> >          * the fault fails. We remain the primary owner of the entry.)
> >          */
> >         if (swapcache)
> > -               zswap_rb_erase(&tree->rbroot, entry);
> > -       spin_unlock(&tree->lock);
> > +               entry = xa_erase(tree, offset);
> > +       else
> > +               entry = xa_load(tree, offset);
>
> This is the place I make the modification for the conflict resolution.
> It depends on the swapcache to execute xa_erase() or xa_load().
> Obviously, the xa_load() will not delete the entry from the tree.
>

The conflict resolution itself LGTM. I'll let you and Johannes decide
on the comment (but FWIW, the original meaning still holds, so I don't
see why we need to fix it).

Reviewed-by: Nhat Pham <nphamcs@...il.com>