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Date: Sun, 30 Sep 2012 17:23:58 +0900 From: Tejun Heo <tj@...nel.org> To: Glauber Costa <glommer@...allels.com> 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 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. Thanks. -- tejun -- 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/
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