linux-kernel - Re: [PATCH] tracing: add ACCOUNT flag for allocations from marked slab caches

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Date:   Mon, 16 May 2022 23:41:27 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Shakeel Butt <shakeelb@...gle.com>, Vasily Averin <vvs@...nvz.org>
Cc:     Roman Gushchin <roman.gushchin@...ux.dev>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        David Rientjes <rientjes@...gle.com>,
        Pekka Enberg <penberg@...nel.org>,
        Christoph Lameter <cl@...ux.com>, kernel@...nvz.org,
        Linux MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Michal Hocko <mhocko@...e.com>,
        Hyeonggon Yoo <42.hyeyoo@...il.com>
Subject: Re: [PATCH] tracing: add ACCOUNT flag for allocations from marked
 slab caches

On 5/16/22 21:10, Shakeel Butt wrote:
> On Mon, May 16, 2022 at 11:53 AM Vasily Averin <vvs@...nvz.org> wrote:
>>
>> Slab caches marked with SLAB_ACCOUNT force accounting for every
>> allocation from this cache even if __GFP_ACCOUNT flag is not passed.
>> Unfortunately, at the moment this flag is not visible in ftrace output,
>> and this makes it difficult to analyze the accounted allocations.
>>
>> This patch adds the __GFP_ACCOUNT flag for allocations from slab caches
>> marked with SLAB_ACCOUNT to the ftrace output.
>>
>> Signed-off-by: Vasily Averin <vvs@...nvz.org>
>> ---
>>  mm/slab.c | 3 +++
>>  mm/slub.c | 3 +++
>>  2 files changed, 6 insertions(+)
>>
>> diff --git a/mm/slab.c b/mm/slab.c
>> index 0edb474edef1..4c3da8dfcbdb 100644
>> --- a/mm/slab.c
>> +++ b/mm/slab.c
>> @@ -3492,6 +3492,9 @@ void *__kmem_cache_alloc_lru(struct kmem_cache *cachep, struct list_lru *lru,
> 
> What about kmem_cache_alloc_node()?
> 
>>  {
>>         void *ret = slab_alloc(cachep, lru, flags, cachep->object_size, _RET_IP_);
>>
>> +       if (cachep->flags & SLAB_ACCOUNT)
> 
> Should this 'if' be unlikely() or should we trace cachep->flags
> explicitly to avoid this branch altogether?

Hm I think ideally the tracepoint accepts cachep instead of current
cachep->*size parameters and does the necessary extraction and
modification in its fast_assign.

> 
>> +               flags |= __GFP_ACCOUNT;
>> +
>>         trace_kmem_cache_alloc(_RET_IP_, ret,
>>                                cachep->object_size, cachep->size, flags);
>>
>> diff --git a/mm/slub.c b/mm/slub.c
>> index ed5c2c03a47a..670bbfef9e49 100644
>> --- a/mm/slub.c
>> +++ b/mm/slub.c
>> @@ -3231,6 +3231,9 @@ void *__kmem_cache_alloc_lru(struct kmem_cache *s, struct list_lru *lru,
>>  {
>>         void *ret = slab_alloc(s, lru, gfpflags, _RET_IP_, s->object_size);
>>
>> +       if (s->flags & SLAB_ACCOUNT)
>> +               gfpflags |= __GFP_ACCOUNT;
>> +
>>         trace_kmem_cache_alloc(_RET_IP_, ret, s->object_size,
>>                                 s->size, gfpflags);
>>
>> --
>> 2.25.1
>>