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

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Date: Tue, 26 Mar 2024 14:03:05 -0700
From: Chris Li <chrisl@...nel.org>
To: Johannes Weiner <hannes@...xchg.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>, linux-kernel@...r.kernel.org, 
	linux-mm@...ck.org, Yosry Ahmed <yosryahmed@...gle.com>, Nhat Pham <nphamcs@...il.com>, 
	"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 1:48 PM Johannes Weiner <hannes@...xchg.org> wrote:
>
> On Tue, Mar 26, 2024 at 11:35:43AM -0700, Chris Li 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
>
> Not sure why you editorialized this? Your patch doesn't change those
> semantics, for which "invalidation" of the backing copy is a much
> better description, given we're also marking the folio dirty again etc.

I was thinking the zswap_invalidate_entry function was deleted now. So
I use the erase to match the xa_erase().
>
> Can you please send a delta fix to undo that?

Sure.

Chris

>
> > @@ -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);
> > +
> > +     if (!entry)
> > +             return false;
> >
> >       if (entry->length)
> >               zswap_decompress(entry, page);
>
> Otherwise, looks good to me
>
> Acked-by: Johannes Weiner <hannes@...xchg.org>
>