On Mon, Mar 8, 2021 at 6:54 AM Paul E. McKenney <paulmck@xxxxxxxxxx> 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@xxxxxxxxx> 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@xxxxxxxxx>
> > > ---
> > > 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
