Re: [PATCH v3 12/28] slab: pass memcg parameter to kmem_cache_create

[Glauber Costa]

On 05/29/2012 06:27 PM, Christoph Lameter wrote:
> On Fri, 25 May 2012, Glauber Costa wrote:
>
> > index 06e4a3e..7c0cdd6 100644
> > --- a/include/linux/slab_def.h
> > +++ b/include/linux/slab_def.h
> > @@ -102,6 +102,13 @@ struct kmem_cache {
> >   	 */
> >   };
> >
> > +static inline void store_orig_align(struct kmem_cache *cachep, int orig_align)
> > +{
> > +#ifdef CONFIG_CGROUP_MEM_RES_CTLR_KMEM
> > +	cachep->memcg_params.orig_align = orig_align;
> > +#endif
> > +}
> > +
>
> Why do you need to store the original alignment? Is the calculated
> alignment not enough?

I think this one can go. You are right.

> > +++ b/mm/slab.c
> > @@ -1729,6 +1729,31 @@ void __init kmem_cache_init_late(void)
> >   	 */
> >   }
> >
> > +static int __init memcg_slab_register_all(void)
> > +{
> > +#ifdef CONFIG_CGROUP_MEM_RES_CTLR_KMEM
> > +	struct kmem_cache *cachep;
> > +	struct cache_sizes *sizes;
> > +
> > +	sizes = malloc_sizes;
> > +
> > +	while (sizes->cs_size != ULONG_MAX) {
> > +		if (sizes->cs_cachep)
> > +			mem_cgroup_register_cache(NULL, sizes->cs_cachep);
> > +		if (sizes->cs_dmacachep)
> > +			mem_cgroup_register_cache(NULL, sizes->cs_dmacachep);
> > +		sizes++;
> > +	}
> > +
> > +	mutex_lock(&cache_chain_mutex);
> > +	list_for_each_entry(cachep,&cache_chain, next)
> > +		mem_cgroup_register_cache(NULL, cachep);
> > +
> > +	mutex_unlock(&cache_chain_mutex);
> > +#endif /* CONFIG_CGROUP_MEM_RES_CTLR_KMEM */
> > +	return 0;
> > +}
>
> Ok this only duplicates the kmalloc arrays. Why not the others?

It does duplicate the others.

First it does a while look on the kmalloc caches, then a 
list_for_each_entry in the rest. You probably missed it.

> > @@ -2331,7 +2350,7 @@ kmem_cache_create (const char *name, size_t size, size_t align,
> >   			continue;
> >   		}
> >
> > -		if (!strcmp(pc->name, name)) {
> > +		if (!memcg&&  !strcmp(pc->name, name)) {
> >   			printk(KERN_ERR
> >   			       "kmem_cache_create: duplicate cache %s\n", name);
> >   			dump_stack();
>
> This implementation means that duplicate cache detection will no longer
> work within a cgroup?

For the slab, yes. For the slub, I check to see if they belong to the 
same memcg.

That said, this can and should be fixed here too, thanks for spotting.

> > @@ -2543,7 +2564,12 @@ kmem_cache_create (const char *name, size_t size, size_t align,
> >   	cachep->ctor = ctor;
> >   	cachep->name = name;
> >
> > +	if (g_cpucache_up>= FULL)
> > +		mem_cgroup_register_cache(memcg, cachep);
>
> What happens if a cgroup was active during creation of slab xxy but
> then a process running in a different cgroup uses that slab to allocate
> memory? Is it charged to the first cgroup?

I don't see this situation ever happening. kmem_cache_create, when 
called directly, will always create a global cache. It doesn't matter 
which cgroups are or aren't active at this time or any other. We create 
copies per-cgroup, but we create it lazily, when someone will touch it.

At that point, which cache will be used depend on which process is using 
it.

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/