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 E97C8C83F2C for ; Mon, 4 Sep 2023 15:41:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1353240AbjIDPlR (ORCPT ); Mon, 4 Sep 2023 11:41:17 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41518 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229492AbjIDPlQ (ORCPT ); Mon, 4 Sep 2023 11:41:16 -0400 Received: from smtp-out2.suse.de (smtp-out2.suse.de [195.135.220.29]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B9E4A83; Mon, 4 Sep 2023 08:41:12 -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-out2.suse.de (Postfix) with ESMTPS id 7A3261F74B; Mon, 4 Sep 2023 15:41:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1693842071; 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=LhJ5sTl63kPWjdnDX0OeDaOslOG+1efqgSGhwPg2LwY=; b=OZAWOqBQsCEfpI3eFuLk7qToZKY+SYTEOk72LyofIJymzTGxX7iTneBlvSQa1EtpyTEC66 9MfOrbNbfb0xXS5YRf8l+Hc4af3UnLICdYto92i8Net2jWr6FpKUI/1z1CgqCZjGdkYx6/ JOU72i1B90DxzFoA2gmVtBFUPLmhYEs= 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 58FA213585; Mon, 4 Sep 2023 15:41:11 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id jP6fEpf69WRyVAAAMHmgww (envelope-from ); Mon, 04 Sep 2023 15:41:11 +0000 Date: Mon, 4 Sep 2023 17:41:10 +0200 From: Michal Hocko To: Michal =?iso-8859-1?Q?Koutn=FD?= Cc: Yosry Ahmed , Andrew Morton , Johannes Weiner , Roman Gushchin , Shakeel Butt , Muchun Song , Ivan Babrou , Tejun Heo , Waiman Long , linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v4 3/4] mm: memcg: let non-unified root stats flushes help unified flushes Message-ID: References: <20230831165611.2610118-1-yosryahmed@google.com> <20230831165611.2610118-4-yosryahmed@google.com> <6tne52ip62ucev7nmnim3m7fhcydnwcytyxynrlxxgaf4cbqea@r4hec425izap> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <6tne52ip62ucev7nmnim3m7fhcydnwcytyxynrlxxgaf4cbqea@r4hec425izap> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon 04-09-23 17:29:14, Michal Koutny wrote: > Hello. > > On Mon, Sep 04, 2023 at 04:50:15PM +0200, Michal Hocko wrote: > > I have hard time to follow why we really want/need this. Does this cause > > any observable changes to the behavior? > > Behavior change depends on how much userspace triggers the root memcg > flush, from nothing to effectively offloading flushing to userspace tasks. > (Theory^^^) > > It keeps stats_flush_threshold up to date representing global error > estimate so that error-tolerant readers may save their time and it keeps > the reasoning about the stats_flush_threshold effect simple. So it also creates an undocumented but userspace visible behavior. Something that userspace might start depending on, right? -- Michal Hocko SUSE Labs