linux-kernel - Re: [PATCH 05/20] mm: zswap: clean up zswap_entry

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Message-ID: <CAKEwX=NjgXOt1f1nb_T=2ZCSZMeCbTW7g5s9VejA_HzKxM-Pmw@mail.gmail.com>
Date: Tue, 30 Jan 2024 08:31:22 -0800
From: Nhat Pham <nphamcs@...il.com>
To: Yosry Ahmed <yosryahmed@...gle.com>
Cc: Johannes Weiner <hannes@...xchg.org>, Andrew Morton <akpm@...ux-foundation.org>, 
	Chengming Zhou <zhouchengming@...edance.com>, linux-mm@...ck.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 05/20] mm: zswap: clean up zswap_entry_put()

On Mon, Jan 29, 2024 at 11:51 PM Yosry Ahmed <yosryahmed@...gle.com> wrote:
>
> On Mon, Jan 29, 2024 at 08:36:41PM -0500, Johannes Weiner wrote:
> > Remove stale comment and unnecessary local variable.
> >
> > Signed-off-by: Johannes Weiner <hannes@...xchg.org>
> > ---
> >  mm/zswap.c | 10 +++-------
> >  1 file changed, 3 insertions(+), 7 deletions(-)
> >
> > diff --git a/mm/zswap.c b/mm/zswap.c
> > index 0c6adaf2fdb6..7a7e8da2b4f8 100644
> > --- a/mm/zswap.c
> > +++ b/mm/zswap.c
> > @@ -546,15 +546,11 @@ static void zswap_entry_get(struct zswap_entry *entry)
> >       entry->refcount++;
> >  }
> >
> > -/* caller must hold the tree lock
> > -* remove from the tree and free it, if nobody reference the entry
> > -*/
> > +/* caller must hold the tree lock */
>
> We should replace all those "caller must hold the tree lock" comments
> with lockdep_assert_held() or assert_spin_locked() or something.
>
> I can send follow up patches on top if you don't want to resend this
> series.

Agree. There's also this:

/* should be called under RCU */
#ifdef CONFIG_MEMCG
static inline struct mem_cgroup *mem_cgroup_from_entry(struct
zswap_entry *entry)
{
return entry->objcg ? obj_cgroup_memcg(entry->objcg) : NULL;
}

which you pointed out in the per-cgroup zswap LRU review :)


>
> >  static void zswap_entry_put(struct zswap_entry *entry)
> >  {
> > -     int refcount = --entry->refcount;
> > -
> > -     WARN_ON_ONCE(refcount < 0);
> > -     if (refcount == 0) {
> > +     WARN_ON_ONCE(!entry->refcount);
> > +     if (--entry->refcount == 0) {
> >               WARN_ON_ONCE(!RB_EMPTY_NODE(&entry->rbnode));
> >               zswap_entry_free(entry);
> >       }
> > --
> > 2.43.0
> >

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