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

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Date:   Mon, 16 May 2022 12:10:19 -0700
From:   Shakeel Butt <shakeelb@...gle.com>
To:     Vasily Averin <vvs@...nvz.org>
Cc:     Roman Gushchin <roman.gushchin@...ux.dev>,
        Vlastimil Babka <vbabka@...e.cz>,
        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>
Subject: Re: [PATCH] tracing: add ACCOUNT flag for allocations from marked
 slab caches

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?

> +               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
>