Re: [PATCH] kmemcg: don't allocate extra memory for root memcg_cache_params

[Andrey Wagin <avagin@gmail.com>]

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2013/8/15 Andrew Morton <akpm@linux-foundation.org>

> On Wed, 14 Aug 2013 14:31:21 +0400 Andrey Vagin <avagin@openvz.org> wrote:
>
> > The memcg_cache_params structure contains the common part and the union,
> > which represents two different types of data: one for root cashes and
> > another for child caches.
> >
> > The size of child data is fixed. The size of the memcg_caches array is
> > calculated in runtime.
> >
> > Currently the size of memcg_cache_params for root caches is calculated
> > incorrectly, because it includes the size of parameters for child caches.
> >
> > ssize_t size = memcg_caches_array_size(num_groups);
> > size *= sizeof(void *);
> >
> > size += sizeof(struct memcg_cache_params);
> >
> > ...
> >
> > --- a/mm/memcontrol.c
> > +++ b/mm/memcontrol.c
> > @@ -3140,7 +3140,7 @@ int memcg_update_cache_size(struct kmem_cache *s,
> int num_groups)
> >               ssize_t size = memcg_caches_array_size(num_groups);
> >
> >               size *= sizeof(void *);
> > -             size += sizeof(struct memcg_cache_params);
> > +             size += sizeof(offsetof(struct memcg_cache_params,
> memcg_caches));
>
> This looks wrong. offsetof() returns size_t, so this is equivalent to
>
>                 size += sizeof(size_t);
>

sizeof doesn't have to be here. I will resend this patch. Thanks.

size += offsetof(struct memcg_cache_params, memcg_caches)


> >               s->memcg_params = kzalloc(size, GFP_KERNEL);
> >               if (!s->memcg_params) {
> > @@ -3183,13 +3183,16 @@ int memcg_update_cache_size(struct kmem_cache
> *s, int num_groups)
> >  int memcg_register_cache(struct mem_cgroup *memcg, struct kmem_cache *s,
> >                        struct kmem_cache *root_cache)
> >  {
> > -     size_t size = sizeof(struct memcg_cache_params);
> > +     size_t size;
> >
> >       if (!memcg_kmem_enabled())
> >               return 0;
> >
> > -     if (!memcg)
> > +     if (!memcg) {
> > +             size = offsetof(struct memcg_cache_params, memcg_caches);
> >               size += memcg_limited_groups_array_size * sizeof(void *);
> > +     } else
> > +             size = sizeof(struct memcg_cache_params);
> >
> >       s->memcg_params = kzalloc(size, GFP_KERNEL);
> >       if (!s->memcg_params)
>
>

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