Re: [PATCH v2 28/47] bcache: dynamically allocate the md-bcache shrinker

[Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>]

On 2023/7/26 15:32, Muchun Song wrote:
> On 2023/7/24 17:43, Qi Zheng wrote:
> > In preparation for implementing lockless slab shrink, use new APIs to
> > dynamically allocate the md-bcache shrinker, so that it can be freed
> > asynchronously using kfree_rcu(). Then it doesn't need to wait for RCU
> > read-side critical section when releasing the struct cache_set.
> >
> > Signed-off-by: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>
> > ---
> >   drivers/md/bcache/bcache.h |  2 +-
> >   drivers/md/bcache/btree.c  | 27 ++++++++++++++++-----------
> >   drivers/md/bcache/sysfs.c  |  3 ++-
> >   3 files changed, 19 insertions(+), 13 deletions(-)
> >
> > diff --git a/drivers/md/bcache/bcache.h b/drivers/md/bcache/bcache.h
> > index 5a79bb3c272f..c622bc50f81b 100644
> > --- a/drivers/md/bcache/bcache.h
> > +++ b/drivers/md/bcache/bcache.h
> > @@ -541,7 +541,7 @@ struct cache_set {
> >       struct bio_set        bio_split;
> >       /* For the btree cache */
> > -    struct shrinker        shrink;
> > +    struct shrinker        *shrink;
> >       /* For the btree cache and anything allocation related */
> >       struct mutex        bucket_lock;
> > diff --git a/drivers/md/bcache/btree.c b/drivers/md/bcache/btree.c
> > index fd121a61f17c..c176c7fc77d9 100644
> > --- a/drivers/md/bcache/btree.c
> > +++ b/drivers/md/bcache/btree.c
> > @@ -667,7 +667,7 @@ static int mca_reap(struct btree *b, unsigned int 
> > min_order, bool flush)
> >   static unsigned long bch_mca_scan(struct shrinker *shrink,
> >                     struct shrink_control *sc)
> >   {
> > -    struct cache_set *c = container_of(shrink, struct cache_set, 
> > shrink);
> > +    struct cache_set *c = shrink->private_data;
> >       struct btree *b, *t;
> >       unsigned long i, nr = sc->nr_to_scan;
> >       unsigned long freed = 0;
> > @@ -734,7 +734,7 @@ static unsigned long bch_mca_scan(struct shrinker 
> > *shrink,
> >   static unsigned long bch_mca_count(struct shrinker *shrink,
> >                      struct shrink_control *sc)
> >   {
> > -    struct cache_set *c = container_of(shrink, struct cache_set, 
> > shrink);
> > +    struct cache_set *c = shrink->private_data;
> >       if (c->shrinker_disabled)
> >           return 0;
> > @@ -752,8 +752,8 @@ void bch_btree_cache_free(struct cache_set *c)
> >       closure_init_stack(&cl);
> > -    if (c->shrink.list.next)
> > -        unregister_shrinker(&c->shrink);
> > +    if (c->shrink)
> > +        shrinker_unregister(c->shrink);
> >       mutex_lock(&c->bucket_lock);
> > @@ -828,14 +828,19 @@ int bch_btree_cache_alloc(struct cache_set *c)
> >           c->verify_data = NULL;
> >   #endif
> > -    c->shrink.count_objects = bch_mca_count;
> > -    c->shrink.scan_objects = bch_mca_scan;
> > -    c->shrink.seeks = 4;
> > -    c->shrink.batch = c->btree_pages * 2;
> > +    c->shrink = shrinker_alloc(0, "md-bcache:%pU", c->set_uuid);
> > +    if (!c->shrink) {
> > +        pr_warn("bcache: %s: could not allocate shrinker\n", __func__);
> > +        return -ENOMEM;
> Seems you have cheanged the semantic of this. In the past,
> it is better to have a shrinker, but now it becomes a mandatory.
> Right? I don't know if it is acceptable. From my point of view,
> just do the cleanup, don't change any behaviour.
Oh, should return 0 here, will do.

> > +    }
> > +
> > +    c->shrink->count_objects = bch_mca_count;
> > +    c->shrink->scan_objects = bch_mca_scan;
> > +    c->shrink->seeks = 4;
> > +    c->shrink->batch = c->btree_pages * 2;
> > +    c->shrink->private_data = c;
> > -    if (register_shrinker(&c->shrink, "md-bcache:%pU", c->set_uuid))
> > -        pr_warn("bcache: %s: could not register shrinker\n",
> > -                __func__);
> > +    shrinker_register(c->shrink);
> >       return 0;
> >   }
> > diff --git a/drivers/md/bcache/sysfs.c b/drivers/md/bcache/sysfs.c
> > index 0e2c1880f60b..45d8af755de6 100644
> > --- a/drivers/md/bcache/sysfs.c
> > +++ b/drivers/md/bcache/sysfs.c
> > @@ -866,7 +866,8 @@ STORE(__bch_cache_set)
> >           sc.gfp_mask = GFP_KERNEL;
> >           sc.nr_to_scan = strtoul_or_return(buf);
> > -        c->shrink.scan_objects(&c->shrink, &sc);
> > +        if (c->shrink)
> > +            c->shrink->scan_objects(c->shrink, &sc);
> >       }
> >       sysfs_strtoul_clamp(congested_read_threshold_us,