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Date:   Mon, 16 May 2022 15:08:48 -0700
From:   Roman Gushchin <roman.gushchin@linux.dev>
To:     Vlastimil Babka <vbabka@suse.cz>
Cc:     Shakeel Butt <shakeelb@google.com>, Vasily Averin <vvs@openvz.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        David Rientjes <rientjes@google.com>,
        Pekka Enberg <penberg@kernel.org>,
        Christoph Lameter <cl@linux.com>, kernel@openvz.org,
        Linux MM <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Michal Hocko <mhocko@suse.com>,
        Hyeonggon Yoo <42.hyeyoo@gmail.com>
Subject: Re: [PATCH] tracing: add ACCOUNT flag for allocations from marked
 slab caches
Message-ID: <YoLLcFFi5UXFEIYg@carbon>
References: <1fd21e25-b095-e055-fc2e-abda640a0575@openvz.org>
 <CALvZod6wmxxigoLVg8Q+upqOkyoh+nPuVT0yx_XTbu8RXYYFgA@mail.gmail.com>
 <8eccb3bc-e6b1-354b-e1de-bd3d896dcb35@suse.cz>
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On Mon, May 16, 2022 at 11:41:27PM +0200, Vlastimil Babka wrote:
> On 5/16/22 21:10, Shakeel Butt wrote:
> > On Mon, May 16, 2022 at 11:53 AM Vasily Averin <vvs@openvz.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@openvz.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.

+1 for fast_assign

Changing flags just for tracing looks a bit excessive.