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Date: Wed, 23 Jul 2014 13:58:18 +0100 From: Mel Gorman <mgorman@...e.de> To: Johannes Weiner <hannes@...xchg.org> Cc: Andrew Morton <akpm@...ux-foundation.org>, Michal Hocko <mhocko@...e.cz>, Linux Kernel <linux-kernel@...r.kernel.org>, Linux-MM <linux-mm@...ck.org> Subject: Re: [PATCH 1/2] mm: Avoid full RCU lookup of memcg for statistics updates On Wed, Jul 23, 2014 at 07:44:49AM -0400, Johannes Weiner wrote: > On Wed, Jul 23, 2014 at 12:24:15PM +0100, Mel Gorman wrote: > > When updating memcg VM statistics like PGFAULT we take the rcu read > > lock and lookup the memcg. For statistic updates this is overkill > > when the process may not belong to a memcg. This patch adds a light > > check to check if a memcg potentially exists. It's race-prone in that > > some VM stats may be missed when a process first joins a memcg but > > that is not serious enough to justify a constant performance penalty. > > Tasks always belong to a memcg, the root group per default. There > isn't really any accounting that could be omitted. > Crap, ok, I had not taken that into account. The lookup of that cannot really be avoided. It's a pity because the stats on the root memcg are not likely to be that interesting. Thanks for reviewing. -- Mel Gorman SUSE Labs -- 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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