From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 02D9EC28D13 for ; Mon, 22 Aug 2022 09:55:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233429AbiHVJzi (ORCPT ); Mon, 22 Aug 2022 05:55:38 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53886 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231327AbiHVJzg (ORCPT ); Mon, 22 Aug 2022 05:55:36 -0400 Received: from smtp-out1.suse.de (smtp-out1.suse.de [195.135.220.28]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7249331DC2; Mon, 22 Aug 2022 02:55:35 -0700 (PDT) Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by smtp-out1.suse.de (Postfix) with ESMTPS id DBD1E33811; Mon, 22 Aug 2022 09:55:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1661162133; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=pVk8EEIWgvaEfpCIwWRQc9Z/K4syoakVdNfp7dj+SUU=; b=vTI1vjq7AQYoaObHpKx6AqFO7egeDT3+5Zw8nBjKDJ/e5jG2pxXAfrrwi1c/XAT0sQyhrq Y7XeCpLthaUYdqfvqduYxMWltnx+WfPf5oVPKVd/4sZ6CD+IQTPgT5GUVCC1ytZKrIRud1 Vcq/KNWC+GfpVZ8hKwsd6h5omqCGVYo= Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by imap2.suse-dmz.suse.de (Postfix) with ESMTPS id B8C0A13523; Mon, 22 Aug 2022 09:55:33 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id 5IWUKpVSA2MefgAAMHmgww (envelope-from ); Mon, 22 Aug 2022 09:55:33 +0000 Date: Mon, 22 Aug 2022 11:55:33 +0200 From: Michal Hocko To: Shakeel Butt Cc: Johannes Weiner , Roman Gushchin , Muchun Song , Michal =?iso-8859-1?Q?Koutn=FD?= , Eric Dumazet , Soheil Hassas Yeganeh , Feng Tang , Oliver Sang , Andrew Morton , lkp@lists.01.org, cgroups@vger.kernel.org, linux-mm@kvack.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/3] mm: page_counter: remove unneeded atomic ops for low/min Message-ID: References: <20220822001737.4120417-1-shakeelb@google.com> <20220822001737.4120417-2-shakeelb@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220822001737.4120417-2-shakeelb@google.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon 22-08-22 00:17:35, Shakeel Butt wrote: > For cgroups using low or min protections, the function > propagate_protected_usage() was doing an atomic xchg() operation > irrespectively. It only needs to do that operation if the new value of > protection is different from older one. This patch does that. This doesn't really explain why. > To evaluate the impact of this optimization, on a 72 CPUs machine, we > ran the following workload in a three level of cgroup hierarchy with top > level having min and low setup appropriately. More specifically > memory.min equal to size of netperf binary and memory.low double of > that. I have hard time to really grasp what is the actual setup and why it matters and why the patch makes any difference. Please elaborate some more here. > $ netserver -6 > # 36 instances of netperf with following params > $ netperf -6 -H ::1 -l 60 -t TCP_SENDFILE -- -m 10K > > Results (average throughput of netperf): > Without (6.0-rc1) 10482.7 Mbps > With patch 14542.5 Mbps (38.7% improvement) > > With the patch, the throughput improved by 38.7% > > Signed-off-by: Shakeel Butt > Reported-by: kernel test robot > --- > mm/page_counter.c | 13 ++++++------- > 1 file changed, 6 insertions(+), 7 deletions(-) > > diff --git a/mm/page_counter.c b/mm/page_counter.c > index eb156ff5d603..47711aa28161 100644 > --- a/mm/page_counter.c > +++ b/mm/page_counter.c > @@ -17,24 +17,23 @@ static void propagate_protected_usage(struct page_counter *c, > unsigned long usage) > { > unsigned long protected, old_protected; > - unsigned long low, min; > long delta; > > if (!c->parent) > return; > > - min = READ_ONCE(c->min); > - if (min || atomic_long_read(&c->min_usage)) { > - protected = min(usage, min); > + protected = min(usage, READ_ONCE(c->min)); > + old_protected = atomic_long_read(&c->min_usage); > + if (protected != old_protected) { I have to cache that code back into brain. It is really subtle thing and it is not really obvious why this is still correct. I will think about that some more but the changelog could help with that a lot. -- Michal Hocko SUSE Labs From mboxrd@z Thu Jan 1 00:00:00 1970 Content-Type: multipart/mixed; boundary="===============2317402912589362322==" MIME-Version: 1.0 From: Michal Hocko To: lkp@lists.01.org Subject: Re: [PATCH 1/3] mm: page_counter: remove unneeded atomic ops for low/min Date: Mon, 22 Aug 2022 11:55:33 +0200 Message-ID: In-Reply-To: <20220822001737.4120417-2-shakeelb@google.com> List-Id: --===============2317402912589362322== Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable On Mon 22-08-22 00:17:35, Shakeel Butt wrote: > For cgroups using low or min protections, the function > propagate_protected_usage() was doing an atomic xchg() operation > irrespectively. It only needs to do that operation if the new value of > protection is different from older one. This patch does that. This doesn't really explain why. > To evaluate the impact of this optimization, on a 72 CPUs machine, we > ran the following workload in a three level of cgroup hierarchy with top > level having min and low setup appropriately. More specifically > memory.min equal to size of netperf binary and memory.low double of > that. I have hard time to really grasp what is the actual setup and why it matters and why the patch makes any difference. Please elaborate some more here. > $ netserver -6 > # 36 instances of netperf with following params > $ netperf -6 -H ::1 -l 60 -t TCP_SENDFILE -- -m 10K > = > Results (average throughput of netperf): > Without (6.0-rc1) 10482.7 Mbps > With patch 14542.5 Mbps (38.7% improvement) > = > With the patch, the throughput improved by 38.7% > = > Signed-off-by: Shakeel Butt > Reported-by: kernel test robot > --- > mm/page_counter.c | 13 ++++++------- > 1 file changed, 6 insertions(+), 7 deletions(-) > = > diff --git a/mm/page_counter.c b/mm/page_counter.c > index eb156ff5d603..47711aa28161 100644 > --- a/mm/page_counter.c > +++ b/mm/page_counter.c > @@ -17,24 +17,23 @@ static void propagate_protected_usage(struct page_cou= nter *c, > unsigned long usage) > { > unsigned long protected, old_protected; > - unsigned long low, min; > long delta; > = > if (!c->parent) > return; > = > - min =3D READ_ONCE(c->min); > - if (min || atomic_long_read(&c->min_usage)) { > - protected =3D min(usage, min); > + protected =3D min(usage, READ_ONCE(c->min)); > + old_protected =3D atomic_long_read(&c->min_usage); > + if (protected !=3D old_protected) { I have to cache that code back into brain. It is really subtle thing and it is not really obvious why this is still correct. I will think about that some more but the changelog could help with that a lot. -- = Michal Hocko SUSE Labs --===============2317402912589362322==--