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 980EFE7849A for ; Mon, 2 Oct 2023 12:18:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236946AbjJBMSk (ORCPT ); Mon, 2 Oct 2023 08:18:40 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52966 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236852AbjJBMSi (ORCPT ); Mon, 2 Oct 2023 08:18:38 -0400 Received: from smtp-out1.suse.de (smtp-out1.suse.de [195.135.220.28]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id CFB369D; Mon, 2 Oct 2023 05:18:33 -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 75102210E0; Mon, 2 Oct 2023 12:18:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1696249112; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=tIkc8wpprjvNQ6XbejVFpwUcXLgpsEm5O3FIVv9vWWY=; b=rfXoQ7EGE9+npzmoeY7FfpoViXbIdglWC3ICWGVjx/3rw1XLefZngDRsNdIa+6Mj7wVuzz cVELoJKQ+CkG5mxIb8kxE3JJByLldqwmyXk84eqH7BMRB1EN/2+nob4t45C/5qEJbd8Fpa lzMwdkSfEqPsh48il+pJrqXEh/Fg4+8= 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 4A5F013434; Mon, 2 Oct 2023 12:18:32 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id gak4Dxi1GmVrIQAAMHmgww (envelope-from ); Mon, 02 Oct 2023 12:18:32 +0000 Date: Mon, 2 Oct 2023 14:18:31 +0200 From: Michal Hocko To: Johannes Weiner Cc: Yosry Ahmed , Nhat Pham , akpm@linux-foundation.org, riel@surriel.com, roman.gushchin@linux.dev, shakeelb@google.com, muchun.song@linux.dev, tj@kernel.org, lizefan.x@bytedance.com, shuah@kernel.org, mike.kravetz@oracle.com, linux-mm@kvack.org, kernel-team@meta.com, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org Subject: Re: [PATCH v2 1/2] hugetlb: memcg: account hugetlb-backed memory in memory controller Message-ID: References: <20230928005723.1709119-1-nphamcs@gmail.com> <20230928005723.1709119-2-nphamcs@gmail.com> <20230929150829.GA16353@cmpxchg.org> <20230929174221.GA19137@cmpxchg.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20230929174221.GA19137@cmpxchg.org> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri 29-09-23 13:42:21, Johannes Weiner wrote: > On Fri, Sep 29, 2023 at 08:11:54AM -0700, Yosry Ahmed wrote: > > On Fri, Sep 29, 2023 at 8:08 AM Johannes Weiner wrote: > > > > > > On Thu, Sep 28, 2023 at 06:18:19PM -0700, Yosry Ahmed wrote: > > > > My concern is the scenario where the memory controller is mounted in > > > > cgroup v1, and cgroup v2 is mounted with memory_hugetlb_accounting. > > > > > > > > In this case it seems like the current code will only check whether > > > > memory_hugetlb_accounting was set on cgroup v2 or not, disregarding > > > > the fact that cgroup v1 did not enable hugetlb accounting. > > > > > > > > I obviously prefer that any features are also added to cgroup v1, > > > > because we still didn't make it to cgroup v2, especially when the > > > > infrastructure is shared. On the other hand, I am pretty sure the > > > > maintainers will not like what I am saying :) > > > > > > I have a weak preference. > > > > > > It's definitely a little weird that the v1 controller's behavior > > > changes based on the v2 mount flag. And that if you want it as an > > > otherwise exclusive v1 user, you'd have to mount a dummy v2. > > > > > > But I also don't see a scenario where it would hurt, or where there > > > would be an unresolvable conflict between v1 and v2 in expressing > > > desired behavior, since the memory controller is exclusive to one. > > > > > > While we could eliminate this quirk with a simple > > > !cgroup_subsys_on_dfl(memory_cgrp_subsys) inside the charge function, > > > it would seem almost punitive to add extra code just to take something > > > away that isn't really a problem and could be useful to some people. > > > > > > If Tejun doesn't object, I'd say let's just keep implied v1 behavior. > > > > I agree that adding extra code to take a feature away from v1 is > > probably too much, but I also think relying on a v2 mount option is > > weird. Would it be too much to just have a v1-specific flag as well > > and use cgroup_subsys_on_dfl(memory_cgrp_subsys) to decide which flag > > to read? > > Yeah, let's not preemptively add explicit new features to cgroup1. > > Since we agree the incidental support is weird, let's filter hugetlb > charging on cgroup_subsys_on_dfl(memory_cgrp_subsys) after all. Agreed. It would be a bad idea to have an implicit behavior change based on v2 mounting options. And I really do not think we want to add this feature to v1. I am not supper thrilled about enabling this for v2 to be completely honest but I do see a demand so I will not object to that. -- Michal Hocko SUSE Labs