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SubjectRe: [PATCH 13/23] slub: create duplicate cache
On Sun, Apr 22, 2012 at 08:53:30PM -0300, Glauber Costa wrote:
> This patch provides kmem_cache_dup(), that duplicates
> a cache for a memcg, preserving its creation properties.
> Object size, alignment and flags are all respected.
>
> When a duplicate cache is created, the parent cache cannot
> be destructed during the child lifetime. To assure this,
> its reference count is increased if the cache creation
> succeeds.
>
> Signed-off-by: Glauber Costa <glommer@parallels.com>
> CC: Christoph Lameter <cl@linux.com>
> CC: Pekka Enberg <penberg@cs.helsinki.fi>
> CC: Michal Hocko <mhocko@suse.cz>
> CC: Kamezawa Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> CC: Johannes Weiner <hannes@cmpxchg.org>
> CC: Suleiman Souhlal <suleiman@google.com>
> ---
> include/linux/memcontrol.h | 3 +++
> include/linux/slab.h | 3 +++
> mm/memcontrol.c | 44 ++++++++++++++++++++++++++++++++++++++++++++
> mm/slub.c | 37 +++++++++++++++++++++++++++++++++++++
> 4 files changed, 87 insertions(+), 0 deletions(-)
>
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index 99e14b9..493ecdd 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -445,6 +445,9 @@ int memcg_css_id(struct mem_cgroup *memcg);
> void mem_cgroup_register_cache(struct mem_cgroup *memcg,
> struct kmem_cache *s);
> void mem_cgroup_release_cache(struct kmem_cache *cachep);
> +extern char *mem_cgroup_cache_name(struct mem_cgroup *memcg,
> + struct kmem_cache *cachep);
> +
> #else
> static inline void mem_cgroup_register_cache(struct mem_cgroup *memcg,
> struct kmem_cache *s)
> diff --git a/include/linux/slab.h b/include/linux/slab.h
> index c7a7e05..909b508 100644
> --- a/include/linux/slab.h
> +++ b/include/linux/slab.h
> @@ -323,6 +323,9 @@ extern void *__kmalloc_track_caller(size_t, gfp_t, unsigned long);
>
> #ifdef CONFIG_CGROUP_MEM_RES_CTLR_KMEM
> #define MAX_KMEM_CACHE_TYPES 400
> +extern struct kmem_cache *kmem_cache_dup(struct mem_cgroup *memcg,
> + struct kmem_cache *cachep);
> +void kmem_cache_drop_ref(struct kmem_cache *cachep);
> #else
> #define MAX_KMEM_CACHE_TYPES 0
> #endif /* CONFIG_CGROUP_MEM_RES_CTLR_KMEM */
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 0015ed0..e881d83 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -467,6 +467,50 @@ struct cg_proto *tcp_proto_cgroup(struct mem_cgroup *memcg)
> EXPORT_SYMBOL(tcp_proto_cgroup);
> #endif /* CONFIG_INET */
>
> +/*
> + * This is to prevent races againt the kmalloc cache creations.
> + * Should never be used outside the core memcg code. Therefore,
> + * copy it here, instead of letting it in lib/
> + */
> +static char *kasprintf_no_account(gfp_t gfp, const char *fmt, ...)
> +{
> + unsigned int len;
> + char *p = NULL;
> + va_list ap, aq;
> +
> + va_start(ap, fmt);
> + va_copy(aq, ap);
> + len = vsnprintf(NULL, 0, fmt, aq);
> + va_end(aq);
> +
> + p = kmalloc_no_account(len+1, gfp);

I can't seem to find kmalloc_no_account() in this patch or may be
I missed it in a previous one?

> + if (!p)
> + goto out;
> +
> + vsnprintf(p, len+1, fmt, ap);
> +
> +out:
> + va_end(ap);
> + return p;
> +}
> +
> +char *mem_cgroup_cache_name(struct mem_cgroup *memcg, struct kmem_cache *cachep)
> +{
> + char *name;
> + struct dentry *dentry = memcg->css.cgroup->dentry;
> +
> + BUG_ON(dentry == NULL);
> +
> + /* Preallocate the space for "dead" at the end */
> + name = kasprintf_no_account(GFP_KERNEL, "%s(%d:%s)dead",
> + cachep->name, css_id(&memcg->css), dentry->d_name.name);
> +
> + if (name)
> + /* Remove "dead" */
> + name[strlen(name) - 4] = '\0';

Why this space for "dead" ? I can't seem to find a reference to that in
the kernel. Is it something I'm missing because of my lack of slab knowledge
or is it something needed in a further patch? In which case this should be
explained in the changelog.

> + return name;
> +}
> +
> /* Bitmap used for allocating the cache id numbers. */
> static DECLARE_BITMAP(cache_types, MAX_KMEM_CACHE_TYPES);
>
> diff --git a/mm/slub.c b/mm/slub.c
> index 86e40cc..2285a96 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -3993,6 +3993,43 @@ struct kmem_cache *kmem_cache_create(const char *name, size_t size,
> }
> EXPORT_SYMBOL(kmem_cache_create);
>
> +#ifdef CONFIG_CGROUP_MEM_RES_CTLR_KMEM
> +struct kmem_cache *kmem_cache_dup(struct mem_cgroup *memcg,
> + struct kmem_cache *s)
> +{
> + char *name;
> + struct kmem_cache *new;
> +
> + name = mem_cgroup_cache_name(memcg, s);
> + if (!name)
> + return NULL;
> +
> + new = kmem_cache_create_memcg(memcg, name, s->objsize, s->align,
> + s->allocflags, s->ctor);
> +
> + /*
> + * We increase the reference counter in the parent cache, to
> + * prevent it from being deleted. If kmem_cache_destroy() is
> + * called for the root cache before we call it for a child cache,
> + * it will be queued for destruction when we finally drop the
> + * reference on the child cache.
> + */
> + if (new) {
> + down_write(&slub_lock);
> + s->refcount++;
> + up_write(&slub_lock);
> + }
> +
> + return new;
> +}
> +
> +void kmem_cache_drop_ref(struct kmem_cache *s)
> +{
> + BUG_ON(s->memcg_params.id != -1);
> + kmem_cache_destroy(s);
> +}
> +#endif
> +
> #ifdef CONFIG_SMP
> /*
> * Use the cpu notifier to insure that the cpu slabs are flushed when
> --
> 1.7.7.6
>
> --
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