Re: + slub-fix-memcg_propagate_slab_attrs.patch added to -mm tree

[Michal Hocko <mhocko@suse.cz>]

On Tue 22-04-14 14:52:57, Vladimir Davydov wrote:
> On 04/22/2014 02:30 PM, Michal Hocko wrote:
> > On Fri 18-04-14 13:08:17, Andrew Morton wrote:
> > [...]
> >> From: Vladimir Davydov <vdavydov@parallels.com>
> >> Subject: slub: fix memcg_propagate_slab_attrs
> >>
> >> After creating a cache for a memcg we should initialize its sysfs attrs
> >> with the values from its parent.  That's what memcg_propagate_slab_attrs
> >> is for.  Currently it's broken - we clearly muddled root-vs-memcg caches
> >> there.  Let's fix it up.
> > 
> > Andrew didn't so I'll do. What is the effect of the mismatch? I am
> > really drowning in that code...
> 
> If we tune a kmem cache's params via sysfs and then create a memcg that
> wants to allocate from the cache, the memcg's copy of the cache will
> have default values of the sysfs params instead of those of the global
> cache.

Ahh, ok, I see. Thanks for the clarification.
 
> >> Signed-off-by: Vladimir Davydov <vdavydov@parallels.com>
> >> Cc: Christoph Lameter <cl@linux.com>
> >> Cc: Pekka Enberg <penberg@kernel.org>
> >> Cc: Michal Hocko <mhocko@suse.cz>
> >> Cc: Johannes Weiner <hannes@cmpxchg.org>
> >> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> >> ---
> >>
> >>  mm/slub.c |   11 +++++++----
> >>  1 file changed, 7 insertions(+), 4 deletions(-)
> >>
> >> diff -puN mm/slub.c~slub-fix-memcg_propagate_slab_attrs mm/slub.c
> >> --- a/mm/slub.c~slub-fix-memcg_propagate_slab_attrs
> >> +++ a/mm/slub.c
> >> @@ -5071,15 +5071,18 @@ static void memcg_propagate_slab_attrs(s
> >>  #ifdef CONFIG_MEMCG_KMEM
> >>  	int i;
> >>  	char *buffer = NULL;
> >> +	struct kmem_cache *root_cache;
> >>  
> >> -	if (!is_root_cache(s))
> >> +	if (is_root_cache(s))
> >>  		return;
> >>  
> >> +	root_cache = s->memcg_params->root_cache;
> >> +
> >>  	/*
> >>  	 * This mean this cache had no attribute written. Therefore, no point
> >>  	 * in copying default values around
> >>  	 */
> >> -	if (!s->max_attr_size)
> >> +	if (!root_cache->max_attr_size)
> >>  		return;
> >>  
> >>  	for (i = 0; i < ARRAY_SIZE(slab_attrs); i++) {
> >> @@ -5101,7 +5104,7 @@ static void memcg_propagate_slab_attrs(s
> >>  		 */
> >>  		if (buffer)
> >>  			buf = buffer;
> >> -		else if (s->max_attr_size < ARRAY_SIZE(mbuf))
> >> +		else if (root_cache->max_attr_size < ARRAY_SIZE(mbuf))
> >>  			buf = mbuf;
> >>  		else {
> >>  			buffer = (char *) get_zeroed_page(GFP_KERNEL);
> >> @@ -5110,7 +5113,7 @@ static void memcg_propagate_slab_attrs(s
> >>  			buf = buffer;
> >>  		}
> >>  
> >> -		attr->show(s->memcg_params->root_cache, buf);
> >> +		attr->show(root_cache, buf);
> >>  		attr->store(s, buf, strlen(buf));
> >>  	}
> >>  
> >> _
> >>
> >> Patches currently in -mm which might be from vdavydov@parallels.com are
> >>
> >> slub-fix-memcg_propagate_slab_attrs.patch
> >> slb-charge-slabs-to-kmemcg-explicitly.patch
> >> mm-get-rid-of-__gfp_kmemcg.patch
> >> mm-get-rid-of-__gfp_kmemcg-fix.patch
> >> slab-document-kmalloc_order.patch
> >>
> > 
> 
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-- 
Michal Hocko
SUSE Labs

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