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    SubjectRe: [PATCH v5 06/18] consider a memcg parameter in kmem_create_cache
    From
    2012/10/19 Glauber Costa <glommer@parallels.com>:

    > diff --git a/mm/memcontrol.c b/mm/memcontrol.c
    > index 6a1e096..59f6d54 100644
    > --- a/mm/memcontrol.c
    > +++ b/mm/memcontrol.c
    > @@ -339,6 +339,12 @@ struct mem_cgroup {
    > #if defined(CONFIG_MEMCG_KMEM) && defined(CONFIG_INET)
    > struct tcp_memcontrol tcp_mem;
    > #endif
    > +#if defined(CONFIG_MEMCG_KMEM)
    > + /* analogous to slab_common's slab_caches list. per-memcg */
    > + struct list_head memcg_slab_caches;
    > + /* Not a spinlock, we can take a lot of time walking the list */
    > + struct mutex slab_caches_mutex;
    > +#endif
    > };

    It is better to change name of "slab_caches_mutex to something
    representing slab cache mutex of memcg.

    > +int memcg_register_cache(struct mem_cgroup *memcg, struct kmem_cache *s)
    > +{
    > + size_t size = sizeof(struct memcg_cache_params);
    > +
    > + if (!memcg_kmem_enabled())
    > + return 0;
    > +
    > + s->memcg_params = kzalloc(size, GFP_KERNEL);
    > + if (!s->memcg_params)
    > + return -ENOMEM;
    > +
    > + if (memcg)
    > + s->memcg_params->memcg = memcg;
    > + return 0;
    > +}

    Now, I don't read full-patchset and I have not enough knowledge about cgroup.
    So I have a question.
    When memcg_kmem_enable, creation kmem_cache of normal user(not
    included in cgroup) also allocate memcg_params.
    Is it right behavior?

    > +void memcg_release_cache(struct kmem_cache *s)
    > +{
    > + kfree(s->memcg_params);
    > +}
    > +
    > /*
    > * We need to verify if the allocation against current->mm->owner's memcg is
    > * possible for the given order. But the page is not allocated yet, so we'll
    > diff --git a/mm/slab.h b/mm/slab.h
    > index 5ee1851..c35ecce 100644
    > --- a/mm/slab.h
    > +++ b/mm/slab.h
    > @@ -35,12 +35,15 @@ extern struct kmem_cache *kmem_cache;
    > /* Functions provided by the slab allocators */
    > extern int __kmem_cache_create(struct kmem_cache *, unsigned long flags);
    >
    > +struct mem_cgroup;
    > #ifdef CONFIG_SLUB
    > -struct kmem_cache *__kmem_cache_alias(const char *name, size_t size,
    > - size_t align, unsigned long flags, void (*ctor)(void *));
    > +struct kmem_cache *
    > +__kmem_cache_alias(struct mem_cgroup *memcg, const char *name, size_t size,
    > + size_t align, unsigned long flags, void (*ctor)(void *));
    > #else
    > -static inline struct kmem_cache *__kmem_cache_alias(const char *name, size_t size,
    > - size_t align, unsigned long flags, void (*ctor)(void *))
    > +static inline struct kmem_cache *
    > +__kmem_cache_alias(struct mem_cgroup *memcg, const char *name, size_t size,
    > + size_t align, unsigned long flags, void (*ctor)(void *))
    > { return NULL; }
    > #endif
    >
    > @@ -98,11 +101,23 @@ static inline bool is_root_cache(struct kmem_cache *s)
    > {
    > return !s->memcg_params || s->memcg_params->is_root_cache;
    > }
    > +
    > +static inline bool cache_match_memcg(struct kmem_cache *cachep,
    > + struct mem_cgroup *memcg)
    > +{
    > + return (is_root_cache(cachep) && !memcg) ||
    > + (cachep->memcg_params->memcg == memcg);
    > +}

    When cachep->memcg_params == NULL and memcg is not NULL, NULL pointer
    deref may be occurred.
    Is there no situation like above?

    > #else
    > static inline bool is_root_cache(struct kmem_cache *s)
    > {
    > return true;
    > }
    >
    > +static inline bool cache_match_memcg(struct kmem_cache *cachep,
    > + struct mem_cgroup *memcg)
    > +{
    > + return true;
    > +}
    > #endif
    > #endif
    > diff --git a/mm/slab_common.c b/mm/slab_common.c
    > index bf4b4f1..f97f7b8 100644
    > --- a/mm/slab_common.c
    > +++ b/mm/slab_common.c
    > @@ -18,6 +18,7 @@
    > #include <asm/cacheflush.h>
    > #include <asm/tlbflush.h>
    > #include <asm/page.h>
    > +#include <linux/memcontrol.h>
    >
    > #include "slab.h"
    >
    > @@ -27,7 +28,8 @@ DEFINE_MUTEX(slab_mutex);
    > struct kmem_cache *kmem_cache;
    >
    > #ifdef CONFIG_DEBUG_VM
    > -static int kmem_cache_sanity_check(const char *name, size_t size)
    > +static int kmem_cache_sanity_check(struct mem_cgroup *memcg, const char *name,
    > + size_t size)
    > {
    > struct kmem_cache *s = NULL;
    >
    > @@ -53,7 +55,7 @@ static int kmem_cache_sanity_check(const char *name, size_t size)
    > continue;
    > }
    >
    > - if (!strcmp(s->name, name)) {
    > + if (cache_match_memcg(s, memcg) && !strcmp(s->name, name)) {
    > pr_err("%s (%s): Cache name already exists.\n",
    > __func__, name);
    > dump_stack();
    > @@ -66,7 +68,8 @@ static int kmem_cache_sanity_check(const char *name, size_t size)
    > return 0;
    > }
    > #else
    > -static inline int kmem_cache_sanity_check(const char *name, size_t size)
    > +static inline int kmem_cache_sanity_check(struct mem_cgroup *memcg,
    > + const char *name, size_t size)
    > {
    > return 0;
    > }
    > @@ -97,8 +100,9 @@ static inline int kmem_cache_sanity_check(const char *name, size_t size)
    > * as davem.
    > */
    >
    > -struct kmem_cache *kmem_cache_create(const char *name, size_t size, size_t align,
    > - unsigned long flags, void (*ctor)(void *))
    > +struct kmem_cache *
    > +kmem_cache_create_memcg(struct mem_cgroup *memcg, const char *name, size_t size,
    > + size_t align, unsigned long flags, void (*ctor)(void *))
    > {
    > struct kmem_cache *s = NULL;
    > int err = 0;
    > @@ -106,7 +110,7 @@ struct kmem_cache *kmem_cache_create(const char *name, size_t size, size_t align
    > get_online_cpus();
    > mutex_lock(&slab_mutex);
    >
    > - if (!kmem_cache_sanity_check(name, size) == 0)
    > + if (!kmem_cache_sanity_check(memcg, name, size) == 0)
    > goto out_locked;

    This compare is somewhat ugly.
    How about "if(kmem_cache_sanity_check(memcg, name, size))"?

    > /*
    > @@ -117,7 +121,7 @@ struct kmem_cache *kmem_cache_create(const char *name, size_t size, size_t align
    > */
    > flags &= CACHE_CREATE_MASK;
    >
    > - s = __kmem_cache_alias(name, size, align, flags, ctor);
    > + s = __kmem_cache_alias(memcg, name, size, align, flags, ctor);
    > if (s)
    > goto out_locked;
    >
    > @@ -126,6 +130,13 @@ struct kmem_cache *kmem_cache_create(const char *name, size_t size, size_t align
    > s->object_size = s->size = size;
    > s->align = align;
    > s->ctor = ctor;
    > +
    > + if (memcg_register_cache(memcg, s)) {
    > + kmem_cache_free(kmem_cache, s);
    > + err = -ENOMEM;
    > + goto out_locked;
    > + }
    > +
    > s->name = kstrdup(name, GFP_KERNEL);
    > if (!s->name) {
    > kmem_cache_free(kmem_cache, s);
    > @@ -135,10 +146,11 @@ struct kmem_cache *kmem_cache_create(const char *name, size_t size, size_t align
    >
    > err = __kmem_cache_create(s, flags);
    > if (!err) {
    > -
    > s->refcount = 1;
    > - list_add(&s->list, &slab_caches);
    > -
    > + if (!memcg)
    > + list_add(&s->list, &slab_caches);
    > + else
    > + memcg_cache_list_add(memcg, s);
    > } else {
    > kfree(s->name);
    > kmem_cache_free(kmem_cache, s);
    > @@ -166,6 +178,13 @@ out_locked:
    >
    > return s;
    > }
    > +
    > +struct kmem_cache *
    > +kmem_cache_create(const char *name, size_t size, size_t align,
    > + unsigned long flags, void (*ctor)(void *))
    > +{
    > + return kmem_cache_create_memcg(NULL, name, size, align, flags, ctor);
    > +}
    > EXPORT_SYMBOL(kmem_cache_create);
    >
    > void kmem_cache_destroy(struct kmem_cache *s)
    > @@ -180,6 +199,7 @@ void kmem_cache_destroy(struct kmem_cache *s)
    >
    > list_del(&s->list);
    >
    > + memcg_release_cache(s);
    > kfree(s->name);
    > kmem_cache_free(kmem_cache, s);
    > } else {
    > diff --git a/mm/slub.c b/mm/slub.c
    > index a34548e..05aefe2 100644
    > --- a/mm/slub.c
    > +++ b/mm/slub.c
    > @@ -31,6 +31,7 @@
    > #include <linux/fault-inject.h>
    > #include <linux/stacktrace.h>
    > #include <linux/prefetch.h>
    > +#include <linux/memcontrol.h>
    >
    > #include <trace/events/kmem.h>
    >
    > @@ -3880,7 +3881,7 @@ static int slab_unmergeable(struct kmem_cache *s)
    > return 0;
    > }
    >
    > -static struct kmem_cache *find_mergeable(size_t size,
    > +static struct kmem_cache *find_mergeable(struct mem_cgroup *memcg, size_t size,
    > size_t align, unsigned long flags, const char *name,
    > void (*ctor)(void *))
    > {
    > @@ -3916,17 +3917,20 @@ static struct kmem_cache *find_mergeable(size_t size,
    > if (s->size - size >= sizeof(void *))
    > continue;
    >
    > + if (!cache_match_memcg(s, memcg))
    > + continue;
    > return s;
    > }
    > return NULL;
    > }
    >
    > -struct kmem_cache *__kmem_cache_alias(const char *name, size_t size,
    > - size_t align, unsigned long flags, void (*ctor)(void *))
    > +struct kmem_cache *
    > +__kmem_cache_alias(struct mem_cgroup *memcg, const char *name, size_t size,
    > + size_t align, unsigned long flags, void (*ctor)(void *))
    > {
    > struct kmem_cache *s;
    >
    > - s = find_mergeable(size, align, flags, name, ctor);
    > + s = find_mergeable(memcg, size, align, flags, name, ctor);
    > if (s) {
    > s->refcount++;
    > /*

    If your intention is that find_mergeable() works for memcg-slab-caches properly,
    it cannot works properly with this code.
    When memcg is not NULL, slab cache is only added to memcg's slab cache list.
    find_mergeable() only interate on original-slab-cache list.
    So memcg slab cache never be mergeable.


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