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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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