linux-kernel - Re: [v8 PATCH 05/13] mm: vmscan: use kvfree_rcu instead of call

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAHbLzkoxVkzYDbFY4DmsQrj+8jv9xbsWAjdRHgKbgNgc0xWaqw@mail.gmail.com>
Date:   Mon, 8 Mar 2021 10:15:03 -0800
From:   Yang Shi <shy828301@...il.com>
To:     paulmck@...nel.org
Cc:     Shakeel Butt <shakeelb@...gle.com>, Roman Gushchin <guro@...com>,
        Kirill Tkhai <ktkhai@...tuozzo.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Dave Chinner <david@...morbit.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...e.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux MM <linux-mm@...ck.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [v8 PATCH 05/13] mm: vmscan: use kvfree_rcu instead of call_rcu

On Mon, Mar 8, 2021 at 6:54 AM Paul E. McKenney <paulmck@...nel.org> wrote:
>
> On Sun, Mar 07, 2021 at 10:13:04PM -0800, Shakeel Butt wrote:
> > On Tue, Feb 16, 2021 at 4:13 PM Yang Shi <shy828301@...il.com> wrote:
> > >
> > > Using kvfree_rcu() to free the old shrinker_maps instead of call_rcu().
> > > We don't have to define a dedicated callback for call_rcu() anymore.
> > >
> > > Signed-off-by: Yang Shi <shy828301@...il.com>
> > > ---
> > >  mm/vmscan.c | 7 +------
> > >  1 file changed, 1 insertion(+), 6 deletions(-)
> > >
> > > diff --git a/mm/vmscan.c b/mm/vmscan.c
> > > index 2e753c2516fa..c2a309acd86b 100644
> > > --- a/mm/vmscan.c
> > > +++ b/mm/vmscan.c
> > > @@ -192,11 +192,6 @@ static inline int shrinker_map_size(int nr_items)
> > >         return (DIV_ROUND_UP(nr_items, BITS_PER_LONG) * sizeof(unsigned long));
> > >  }
> > >
> > > -static void free_shrinker_map_rcu(struct rcu_head *head)
> > > -{
> > > -       kvfree(container_of(head, struct memcg_shrinker_map, rcu));
> > > -}
> > > -
> > >  static int expand_one_shrinker_map(struct mem_cgroup *memcg,
> > >                                    int size, int old_size)
> > >  {
> > > @@ -219,7 +214,7 @@ static int expand_one_shrinker_map(struct mem_cgroup *memcg,
> > >                 memset((void *)new->map + old_size, 0, size - old_size);
> > >
> > >                 rcu_assign_pointer(memcg->nodeinfo[nid]->shrinker_map, new);
> > > -               call_rcu(&old->rcu, free_shrinker_map_rcu);
> > > +               kvfree_rcu(old);
> >
> > Please use kvfree_rcu(old, rcu) instead of kvfree_rcu(old). The single
> > param can call synchronize_rcu().
>
> Especially given that you already have the ->rcu field that the
> two-argument form requires.
>
> The reason for using the single-argument form is when you have lots of
> little data structures, such that getting rid of that rcu_head structure
> is valuable enough to be worth the occasional call to synchronize_rcu().
> However, please note that this call to synchronize_rcu() happens only
> under OOM conditions.

Thanks, Shakeel and Paul. I didn't realize the difference. Will use
the two params form in the new version.

>
>                                                         Thanx, Paul