Messages in this thread |  | | | Date | Tue, 29 May 2012 19:56:23 +0400 | | From | Glauber Costa <> | | Subject | Re: [PATCH v3 13/28] slub: create duplicate cache |
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On 05/29/2012 06:36 PM, Christoph Lameter wrote: > On Fri, 25 May 2012, Glauber Costa wrote: > >> index dacd1fb..4689034 100644 >> --- a/mm/memcontrol.c >> +++ b/mm/memcontrol.c >> @@ -467,6 +467,23 @@ struct cg_proto *tcp_proto_cgroup(struct mem_cgroup *memcg) >> EXPORT_SYMBOL(tcp_proto_cgroup); >> #endif /* CONFIG_INET */ >> >> +char *mem_cgroup_cache_name(struct mem_cgroup *memcg, struct kmem_cache *cachep) >> +{ >> + char *name; >> + struct dentry *dentry; >> + >> + rcu_read_lock(); >> + dentry = rcu_dereference(memcg->css.cgroup->dentry); >> + rcu_read_unlock(); >> + >> + BUG_ON(dentry == NULL); >> + >> + name = kasprintf(GFP_KERNEL, "%s(%d:%s)", >> + cachep->name, css_id(&memcg->css), dentry->d_name.name); >> + >> + return name; >> +} > > Function allocates a string that is supposed to be disposed of by the > caller. That needs to be documented and maybe even the name needs to > reflect that.
Okay, I can change it.
>> --- a/mm/slub.c >> +++ b/mm/slub.c >> @@ -4002,6 +4002,38 @@ 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& ~SLAB_PANIC), s->ctor); > > Hmmm... A full duplicate of the slab cache? We may have many sparsely > used portions of the per node and per cpu structure as a result.
I've already commented on patch 0, but I will repeat it here. This approach leads to more fragmentation, yes, but this is exactly to be less intrusive.
With a full copy, all I need to do is:
1) relay the allocation to the right cache. 2) account for a new page when it is needed.
How does the cache work from inside? I don't care.
Accounting pages seems just crazy to me. If new allocators come in the future, organizing the pages in a different way, instead of patching it here and there, we need to totally rewrite this.
If those allocators happen to depend on a specific placement for performance, then we're destroying this as well too.
> >> + * 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); >> + } > > Why do you need to increase the refcount? You made a full copy right?
Yes, but I don't want this copy to go away while we have other caches around.
So, in the memcg internals, I used a different reference counter, to avoid messing with this one. I could use that, and leave the original refcnt alone. Would you prefer this?
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