linux-kernel - Re: [PATCH v3 04/13] kmem accounting basic infrastructure

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Mon, 1 Oct 2012 12:45:11 +0400
From:	Glauber Costa <glommer@...allels.com>
To:	Tejun Heo <tj@...nel.org>
CC:	Mel Gorman <mgorman@...e.de>, Michal Hocko <mhocko@...e.cz>,
	<linux-kernel@...r.kernel.org>, <cgroups@...r.kernel.org>,
	<kamezawa.hiroyu@...fujitsu.com>, <devel@...nvz.org>,
	<linux-mm@...ck.org>, Suleiman Souhlal <suleiman@...gle.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	David Rientjes <rientjes@...gle.com>,
	Johannes Weiner <hannes@...xchg.org>
Subject: Re: [PATCH v3 04/13] kmem accounting basic infrastructure

On 09/30/2012 12:23 PM, Tejun Heo wrote:
> Hello, Glauber.
> 
> On Thu, Sep 27, 2012 at 10:30:36PM +0400, Glauber Costa wrote:
>>> But that happens only when pages enter and leave slab and if it still
>>> is significant, we can try to further optimize charging.  Given that
>>> this is only for cases where memcg is already in use and we provide a
>>> switch to disable it globally, I really don't think this warrants
>>> implementing fully hierarchy configuration.
>>
>> Not totally true. We still have to match every allocation to the right
>> cache, and that is actually our heaviest hit, responsible for the 2, 3 %
>> we're seeing when this is enabled. It is the kind of path so hot that
>> people frown upon branches being added, so I don't think we'll ever get
>> this close to being free.
> 
> Sure, depening on workload, any addition to alloc/free could be
> noticeable.  I don't know.  I'll write more about it when replying to
> Michal's message.  BTW, __memcg_kmem_get_cache() does seem a bit
> heavy.  I wonder whether indexing from cache side would make it
> cheaper?  e.g. something like the following.
> 
> 	kmem_cache *__memcg_kmem_get_cache(cachep, gfp)
> 	{
> 		struct kmem_cache *c;
> 
> 		c = cachep->memcg_params->caches[percpu_read(kmemcg_slab_idx)];
> 		if (likely(c))
> 			return c;
> 		/* try to create and then fall back to cachep */
> 	}
> 
> where kmemcg_slab_idx is updated from sched notifier (or maybe add and
> use current->kmemcg_slab_idx?).  You would still need __GFP_* and
> in_interrupt() tests but current->mm and PF_KTHREAD tests can be
> rolled into index selection.
> 

How big would this array be? there can be a lot more kmem_caches than
there are memcgs. That is why it is done from memcg side.

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