x27;t hold off RCU here so what guarantees a racing global
shrinker walk doesn't trip over this shrinker_put() call dropping
the refcount to zero and freeing occuring in a different context...
> + /*
> + * We have already exited the read-side of rcu critical section
> + * before calling do_shrink_slab(), the shrinker_info may be
> + * released in expand_one_shrinker_info(), so reacquire the
> + * shrinker_info.
> + */
> + index++;
> + goto again;
With that, what makes the use of shrinker_info in
xchg_nr_deferred_memcg() in do_shrink_slab() coherent and valid?
-Dave.
--
Dave Chinner
da...@fromorbit.com
f (!shrinker)
> return;
>
> + if (shrinker->flags & SHRINKER_REGISTERED) {
> + shrinker_put(shrinker);
> + wait_for_completion(&shrinker->done);
> + }
Needs a comment explaining why we need to wait here...
> +
> down_write(&shrinker_rwsem);
urn 0;
> @@ -419,56 +470,63 @@ static unsigned long shrink_slab_memcg(gfp_t gfp_mask,
> int nid,
> if (unlikely(!info))
> goto unlock;
>
> - for_each_set_bit(i, info->map, info->map_nr_max) {
> - struct shrink_control sc = {
> - .gfp_mask = gfp_mask,
> - .nid = nid,
> - .memcg = memcg,
> - };
> - struct shrinker *shrinker;
> + for (; index < shriner_id_to_index(info->map_nr_max); index++) {
> + struct shrinker_info_unit *unit;
This adds another layer of indent to shrink_slab_memcg(). Please
factor it first so that the code ends up being readable. Doing that
first as a separate patch will also make the actual algorithm
changes in this patch be much more obvious - this huge hunk of
diff is pretty much impossible to review...
-Dave.
--
Dave Chinner
da...@fromorbit.com
lowing cases.
> This commit uses the refcount+RCU method [5] proposed by Dave Chinner
> to re-implement the lockless global slab shrink. The memcg slab shrink is
> handled in the subsequent patch.
> ---
> include/linux/shrinker.h | 17 ++
>
e "this is obviously correct" that what we have
now.
> So not adding that super simple
> helper is not exactly the best choice in my opinion.
Each to their own - I much prefer the existing style/API over having
to go look up a helper function every time I want to check some
random shrinker has been set up correctly
-Dave.
--
Dave Chinner
da...@fromorbit.com
On Wed, Jul 26, 2023 at 05:14:09PM +0800, Qi Zheng wrote:
> On 2023/7/26 16:08, Dave Chinner wrote:
> > On Mon, Jul 24, 2023 at 05:43:51PM +0800, Qi Zheng wrote:
> > > @@ -122,6 +126,13 @@ void shrinker_free_non_registered(struct shrinker
> > > *shrinker);
> >
gt; We used to implement the lockless slab shrink with SRCU [2], but then
> kernel test robot reported -88.8% regression in
> stress-ng.ramfs.ops_per_sec test case [3], so we reverted it [4].
>
> This commit uses the refcount+RCU method [5] proposed by Dave Chinner
> to re-implement th
RE)
unregister_memcg_shrinker(shrinker);
up_write(&shrinker_rwsem);
if (debugfs_entry)
shrinker_debugfs_remove(debugfs_entry, debugfs_id);
kfree(shrinker->nr_deferred);
kfree(shrinker);
}
EXPORT_SYMBOL_GPL(shrinker_free);
--
Dave Chinner
da...@fromorbit.com
