Home » Mailing lists » Devel » [PATCH v3 00/28] kmem limitation for memcg
| Re: [PATCH v3 13/28] slub: create duplicate cache [message #46574 is a reply to message #46565] |
Tue, 29 May 2012 15:56   |
Glauber Costa
Messages: 916
Registered: October 2011
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Senior Member |
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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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