linux-kernel - Re: [PATCH-next] mm, memcg: Add ":deact" tag for reparented kmem caches in memcg

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Date:   Thu, 27 Jun 2019 14:45:00 -0400
From:   Waiman Long <longman@...hat.com>
To:     Roman Gushchin <guro@...com>
Cc:     Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Michal Hocko <mhocko@...nel.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Shakeel Butt <shakeelb@...gle.com>,
        Vladimir Davydov <vdavydov.dev@...il.com>
Subject: Re: [PATCH-next] mm, memcg: Add ":deact" tag for reparented kmem
 caches in memcg_slabinfo

On 6/26/19 3:58 PM, Roman Gushchin wrote:
> On Fri, Jun 21, 2019 at 01:30:05PM -0400, Waiman Long wrote:
>> With Roman's kmem cache reparent patch, multiple kmem caches of the same
>> type can be seen attached to the same memcg id. All of them, except
>> maybe one, are reparent'ed kmem caches. It can be useful to tag those
>> reparented caches by adding a new slab flag "SLAB_DEACTIVATED" to those
>> kmem caches that will be reparent'ed if it cannot be destroyed completely.
>>
>> For the reparent'ed memcg kmem caches, the tag ":deact" will now be
>> shown in <debugfs>/memcg_slabinfo.
>>
>> Signed-off-by: Waiman Long <longman@...hat.com>
> Hi Waiman!
>
> Sorry for the late reply. The patch overall looks good to me,
> except one nit. Please feel free to use my ack:
> Acked-by: Roman Gushchin <guro@...com>
>
>> ---
>>  include/linux/slab.h |  4 ++++
>>  mm/slab.c            |  1 +
>>  mm/slab_common.c     | 14 ++++++++------
>>  mm/slub.c            |  1 +
>>  4 files changed, 14 insertions(+), 6 deletions(-)
>>
>> diff --git a/include/linux/slab.h b/include/linux/slab.h
>> index fecf40b7be69..19ab1380f875 100644
>> --- a/include/linux/slab.h
>> +++ b/include/linux/slab.h
>> @@ -116,6 +116,10 @@
>>  /* Objects are reclaimable */
>>  #define SLAB_RECLAIM_ACCOUNT	((slab_flags_t __force)0x00020000U)
>>  #define SLAB_TEMPORARY		SLAB_RECLAIM_ACCOUNT	/* Objects are short-lived */
>> +
>> +/* Slab deactivation flag */
>> +#define SLAB_DEACTIVATED	((slab_flags_t __force)0x10000000U)
>> +
>>  /*
>>   * ZERO_SIZE_PTR will be returned for zero sized kmalloc requests.
>>   *
>> diff --git a/mm/slab.c b/mm/slab.c
>> index a2e93adf1df0..e8c7743fc283 100644
>> --- a/mm/slab.c
>> +++ b/mm/slab.c
>> @@ -2245,6 +2245,7 @@ int __kmem_cache_shrink(struct kmem_cache *cachep)
>>  #ifdef CONFIG_MEMCG
>>  void __kmemcg_cache_deactivate(struct kmem_cache *cachep)
>>  {
>> +	cachep->flags |= SLAB_DEACTIVATED;
> A nit: it can be done from kmemcg_cache_deactivate() instead,
> and then you don't have to do it in slab and slub separately.
>
> Since it's not slab- or slub-specific code, it'd be better, IMO,
> to put it into slab_common.c.

Thanks for the suggestion.

You are right. It will be cleaner to set the flag in
kmemcg_cache_deactivate(). I have just sent out a v2 patch to do that.

Cheers,
Longman