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SubjectRe: [PATCH] slab, slub: skip unnecessary kasan_cache_shutdown()
On Tue, 27 Mar 2018, Shakeel Butt wrote:

> On Tue, Mar 27, 2018 at 5:16 PM, David Rientjes <rientjes@google.com> wrote:
> > On Tue, 27 Mar 2018, Shakeel Butt wrote:
> >
> >> diff --git a/mm/kasan/kasan.c b/mm/kasan/kasan.c
> >> index 49fffb0ca83b..135ce2838c89 100644
> >> --- a/mm/kasan/kasan.c
> >> +++ b/mm/kasan/kasan.c
> >> @@ -382,7 +382,8 @@ void kasan_cache_shrink(struct kmem_cache *cache)
> >>
> >> void kasan_cache_shutdown(struct kmem_cache *cache)
> >> {
> >> - quarantine_remove_cache(cache);
> >> + if (!__kmem_cache_empty(cache))
> >> + quarantine_remove_cache(cache);
> >> }
> >>
> >> size_t kasan_metadata_size(struct kmem_cache *cache)
> >> diff --git a/mm/slab.c b/mm/slab.c
> >> index 9212c64bb705..b59f2cdf28d1 100644
> >> --- a/mm/slab.c
> >> +++ b/mm/slab.c
> >> @@ -2291,6 +2291,18 @@ static int drain_freelist(struct kmem_cache *cache,
> >> return nr_freed;
> >> }
> >>
> >> +bool __kmem_cache_empty(struct kmem_cache *s)
> >> +{
> >> + int node;
> >> + struct kmem_cache_node *n;
> >> +
> >> + for_each_kmem_cache_node(s, node, n)
> >> + if (!list_empty(&n->slabs_full) ||
> >> + !list_empty(&n->slabs_partial))
> >> + return false;
> >> + return true;
> >> +}
> >> +
> >> int __kmem_cache_shrink(struct kmem_cache *cachep)
> >> {
> >> int ret = 0;
> >> diff --git a/mm/slab.h b/mm/slab.h
> >> index e8981e811c45..68bdf498da3b 100644
> >> --- a/mm/slab.h
> >> +++ b/mm/slab.h
> >> @@ -166,6 +166,7 @@ static inline slab_flags_t kmem_cache_flags(unsigned int object_size,
> >> SLAB_TEMPORARY | \
> >> SLAB_ACCOUNT)
> >>
> >> +bool __kmem_cache_empty(struct kmem_cache *);
> >> int __kmem_cache_shutdown(struct kmem_cache *);
> >> void __kmem_cache_release(struct kmem_cache *);
> >> int __kmem_cache_shrink(struct kmem_cache *);
> >> diff --git a/mm/slub.c b/mm/slub.c
> >> index 1edc8d97c862..44aa7847324a 100644
> >> --- a/mm/slub.c
> >> +++ b/mm/slub.c
> >> @@ -3707,6 +3707,17 @@ static void free_partial(struct kmem_cache *s, struct kmem_cache_node *n)
> >> discard_slab(s, page);
> >> }
> >>
> >> +bool __kmem_cache_empty(struct kmem_cache *s)
> >> +{
> >> + int node;
> >> + struct kmem_cache_node *n;
> >> +
> >> + for_each_kmem_cache_node(s, node, n)
> >> + if (n->nr_partial || slabs_node(s, node))
> >> + return false;
> >> + return true;
> >> +}
> >> +
> >> /*
> >> * Release all resources used by a slab cache.
> >> */
> >
> > Any reason not to just make quarantine_remove_cache() part of
> > __kmem_cache_shutdown() instead of duplicating its logic?
>
> Can you please explain what you mean by making
> quarantine_remove_cache() part of __kmem_cache_shutdown()? Do you mean
> calling quarantine_remove_cache() inside __kmem_cache_shutdown()? The
> __kmem_cache_shutdown() of both SLAB & SLUB does per-cpu
> draining/flushing and we want the free the quarantined objects before
> that. So, I am not sure how to incorporate quarantine_remove_cache()
> into __kmem_cache_shutdown() without duplicating the for-loop &
> if-condition.
>

__kmem_cache_empty() is largely a copy and paste of
__kmem_cache_shutdown() logic, is there no way to simplify this? I was
thinking of generalizing the iteration (for_each_kmem_cach_node_nonempty?)
that eliminates the need for __kmem_cache_empty().

kasan_cache_shutdown() would do

for_each_kmem_cache_node_nonempty(cache, node, n) {
quarantine_remove_cache(cache);
break;
}

and __kmem_cache_shutdown() would use it for the iteration over
kmem_cache_node's to drain.

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