linux-kernel - Re: [PATCH] slab, slub: skip unnecessary kasan_cache

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Date:   Tue, 27 Mar 2018 22:41:15 -0700
From:   Shakeel Butt <shakeelb@...gle.com>
To:     David Rientjes <rientjes@...gle.com>
Cc:     Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Alexander Potapenko <glider@...gle.com>,
        Greg Thelen <gthelen@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] slab, slub: skip unnecessary kasan_cache_shutdown()

On Tue, Mar 27, 2018 at 5:16 PM, David Rientjes <rientjes@...gle.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.