From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-lf0-f47.google.com (mail-lf0-f47.google.com [209.85.215.47]) by kanga.kvack.org (Postfix) with ESMTP id 5749D6B0253 for ; Mon, 30 Nov 2015 11:14:07 -0500 (EST) Received: by lffu14 with SMTP id u14so203921514lff.1 for ; Mon, 30 Nov 2015 08:14:06 -0800 (PST) Received: from relay.parallels.com (relay.parallels.com. [195.214.232.42]) by mx.google.com with ESMTPS id rq3si10825212lbb.14.2015.11.30.08.14.05 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 30 Nov 2015 08:14:05 -0800 (PST) Date: Mon, 30 Nov 2015 19:13:46 +0300 From: Vladimir Davydov Subject: Re: [PATCH 13/13] mm: memcontrol: hook up vmpressure to socket pressure Message-ID: <20151130161346.GD24704@esperanza> References: <1448401925-22501-1-git-send-email-hannes@cmpxchg.org> <20151124215940.GB1373@cmpxchg.org> <20151130113628.GB24704@esperanza> <20151130155838.GB30243@cmpxchg.org> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <20151130155838.GB30243@cmpxchg.org> Sender: owner-linux-mm@kvack.org List-ID: To: Johannes Weiner Cc: Andrew Morton , David Miller , Michal Hocko , Tejun Heo , Eric Dumazet , netdev@vger.kernel.org, linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@fb.com On Mon, Nov 30, 2015 at 10:58:38AM -0500, Johannes Weiner wrote: > On Mon, Nov 30, 2015 at 02:36:28PM +0300, Vladimir Davydov wrote: > > Suppose we have the following cgroup configuration. > > > > A __ B > > \_ C > > > > A is empty (which is natural for the unified hierarchy AFAIU). B has > > some workload running in it, and C generates socket pressure. Due to the > > socket pressure coming from C we start reclaim in A, which results in > > thrashing of B, but we might not put sockets under pressure in A or C, > > because vmpressure does not account pages scanned/reclaimed in B when > > generating a vmpressure event for A or C. This might result in > > aggressive reclaim and thrashing in B w/o generating a signal for C to > > stop growing socket buffers. > > > > Do you think such a situation is possible? If so, would it make sense to > > switch to post-order walk in shrink_zone and pass sub-tree > > scanned/reclaimed stats to vmpressure for each scanned memcg? > > In that case the LRU pages in C would experience pressure as well, > which would then reign in the sockets in C. There must be some LRU > pages in there, otherwise who is creating socket pressure? > > The same applies to shrinkers. All secondary reclaim is driven by LRU > reclaim results. > > I can see that there is some unfairness in distributing memcg reclaim > pressure purely based on LRU size, because there are scenarios where > the auxiliary objects (incl. sockets, but mostly shrinker pools) > amount to a significant portion of the group's memory footprint. But > substitute group for NUMA node and we've had this behavior for > years. I'm not sure it's actually a problem in practice. > Fiar enough. Let's wait until we hit this problem in real world then. The patch looks good to me. Reviewed-by: Vladimir Davydov Thanks, Vladimir -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org