On Fri, 31 Jan 2014, Vladimir Davydov wrote:
> > diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> > --- a/mm/memcontrol.c
> > +++ b/mm/memcontrol.c
> > @@ -637,6 +637,9 @@ int memcg_limited_groups_array_size;
> > * better kept as an internal representation in cgroup.c. In any case, the
> > * cgrp_id space is not getting any smaller, and we don't have to necessarily
> > * increase ours as well if it increases.
> > + *
> > + * Updates to MAX_SIZE should update the space for the memcg name in
> > + * memcg_create_kmem_cache().
> > */
> > #define MEMCG_CACHES_MIN_SIZE 4
> > #define MEMCG_CACHES_MAX_SIZE MEM_CGROUP_ID_MAX
> > @@ -3400,8 +3403,10 @@ void mem_cgroup_destroy_cache(struct kmem_cache *cachep)
> > static struct kmem_cache *memcg_create_kmem_cache(struct mem_cgroup *memcg,
> > struct kmem_cache *s)
> > {
> > - char *name = NULL;
> > struct kmem_cache *new;
> > + const char *cgrp_name;
> > + char *name = NULL;
> > + size_t len;
> >
> > BUG_ON(!memcg_can_account_kmem(memcg));
> >
> > @@ -3409,9 +3414,22 @@ static struct kmem_cache *memcg_create_kmem_cache(struct mem_cgroup *memcg,
> > if (unlikely(!name))
> > return NULL;
> >
> > + /*
> > + * Format of a memcg's kmem cache name:
> > + * <cache-name>(<memcg-id>:<cgroup-name>)
> > + */
> > + len = strlen(s->name);
> > + /* Space for parentheses, colon, terminator */
> > + len += 4;
> > + /* MEMCG_CACHES_MAX_SIZE is USHRT_MAX */
> > + len += 5;
> > + BUILD_BUG_ON(MEMCG_CACHES_MAX_SIZE > USHRT_MAX);
> > +
>
> This looks cumbersome, IMO. Let's leave it as is for now. AFAIK,
> cgroup_name() will be reworked soon so that it won't require RCU-context
> (https://lkml.org/lkml/2014/1/28/530). Therefore, it will be possible to
> get rid of this pointless tmp_name allocation by making
> kmem_cache_create_memcg() take not just name, but printf-like format +
> vargs.
>
You believe it's less cumbersome to do two memory allocations to figure
out how much memory you really need to allocate rather than just
calculating the necessary size?
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