LKML Archive on
help / color / mirror / Atom feed
From: Shakeel Butt <>
To: Michal Hocko <>
Cc: Jan Kara <>, Amir Goldstein <>,
	Christoph Lameter <>,
	Pekka Enberg <>,
	David Rientjes <>,
	Joonsoo Kim <>,
	Andrew Morton <>,
	Greg Thelen <>,
	Johannes Weiner <>,
	Vladimir Davydov <>,
	Mel Gorman <>, Vlastimil Babka <>,
	linux-fsdevel <>,
	Linux MM <>, Cgroups <>,
	LKML <>
Subject: Re: [PATCH v3 1/2] mm: memcg: remote memcg charging for kmem allocations
Date: Tue, 13 Mar 2018 10:55:18 -0700	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

On Tue, Mar 13, 2018 at 6:49 AM, Michal Hocko <> wrote:
> On Wed 21-02-18 14:37:56, Shakeel Butt wrote:
> [...]
>> +#ifdef CONFIG_MEMCG
>> +static inline struct mem_cgroup *memalloc_memcg_save(struct mem_cgroup *memcg)
>> +{
>> +     struct mem_cgroup *old_memcg = current->target_memcg;
>> +     current->target_memcg = memcg;
>> +     return old_memcg;
>> +}
> So you are relying that the caller will handle the reference counting
> properly? I do not think this is a good idea.

For the fsnotify use-case, this assumption makes sense as fsnotify has
an abstraction of fsnotify_group which is created by the
person/process interested in the events and thus can be used to hold
the reference to the person/process's memcg. Another use-case I have
in mind is the filesystem mount. Basically attaching a mount with a
memcg and thus all user pages and kmem allocations (inodes, dentries)
for that mount will be charged to the attached memcg. In this use-case
the super_block is the perfect structure to hold the reference to the

If in future we find a use-case where this assumption does not make
sense we can evolve the API and since this is kernel internal API, it
should not be hard to evolve.

> Also do we need some kind
> of debugging facility to detect unbalanced save/restore scopes?

I am not sure, I didn't find other similar patterns (like PF_MEMALLOC)
having debugging facility. Maybe we can add such debugging facility
when we find more users other than kmalloc & kmem_cache_alloc. Vmalloc
may be one but I could not think of a use-case for vmalloc for remote
charging, so, no need to add more code at this time.

> [...]
>> @@ -2260,7 +2269,10 @@ struct kmem_cache *memcg_kmem_get_cache(struct kmem_cache *cachep)
>>       if (current->memcg_kmem_skip_account)
>>               return cachep;
>> -     memcg = get_mem_cgroup_from_mm(current->mm);
>> +     if (current->target_memcg)
>> +             memcg = get_mem_cgroup(current->target_memcg);
>> +     if (!memcg)
>> +             memcg = get_mem_cgroup_from_mm(current->mm);
>>       kmemcg_id = READ_ONCE(memcg->kmemcg_id);
>>       if (kmemcg_id < 0)
>>               goto out;
> You are also adding one branch for _each_ charge path even though the
> usecase is rather limited.

I understand the concern but the charging path, IMO, is much complex
than just one or couple of additional branches. I can run a simple
microbenchmark to see if there is anything noticeable here.

> I will have to think about this approach more. It is clearly less code
> than your previous attempt but I cannot say I would be really impressed.

Thanks for your time.

  reply	other threads:[~2018-03-13 17:55 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-02-21 22:37 [PATCH v3 0/2] Directed kmem charging Shakeel Butt
2018-02-21 22:37 ` [PATCH v3 1/2] mm: memcg: remote memcg charging for kmem allocations Shakeel Butt
2018-03-13 13:49   ` Michal Hocko
2018-03-13 17:55     ` Shakeel Butt [this message]
2018-03-15 17:49       ` Michal Hocko
2018-03-15 18:25         ` Shakeel Butt
2018-04-06 17:36         ` [PATCH] " Shakeel Butt
2018-02-21 22:37 ` [PATCH v3 2/2] fs: fsnotify: account fsnotify metadata to kmemcg Shakeel Butt

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to='' \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).