From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=suse.com header.i=@suse.com header.b="OOXAB+Dp" Received: from smtp-out1.suse.de (smtp-out1.suse.de [IPv6:2a07:de40:b251:101:10:150:64:1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 30B342117; Mon, 27 Nov 2023 07:29:59 -0800 (PST) Received: from imap1.dmz-prg2.suse.org (imap1.dmz-prg2.suse.org [10.150.64.97]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by smtp-out1.suse.de (Postfix) with ESMTPS id 8CB2A21B58; Mon, 27 Nov 2023 15:29:57 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1701098997; 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=ll683VjO5cgdZEXvfYTUzLYylEdUG/UQv49Lu4Sc7rA=; b=OOXAB+DpFUt4iwizIQsg9NdOIv7EkWhpXPvrvm3xSPIkYK01e48JBaP6McNQXVt1W4HMcp FzhsJfz4OLu8cI2pA+kFgSSwrdgoVb/idRWXuLd+Fx/rh355mLKnibOH8SOrq1VdRhoTdr woqZH0y3y+TGG/qALZCHEensDf8Z/lc= Received: from imap1.dmz-prg2.suse.org (localhost [127.0.0.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by imap1.dmz-prg2.suse.org (Postfix) with ESMTPS id 714C11367B; Mon, 27 Nov 2023 15:29:57 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id e1MKGvW1ZGVHRQAAD6G6ig (envelope-from ); Mon, 27 Nov 2023 15:29:57 +0000 Date: Mon, 27 Nov 2023 16:29:56 +0100 From: Michal Hocko To: Gregory Price Cc: Andrew Morton , Gregory Price , linux-mm@kvack.org, linux-doc@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-api@vger.kernel.org, linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, arnd@arndb.de, tglx@linutronix.de, luto@kernel.org, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, tj@kernel.org, ying.huang@intel.com Subject: Re: [RFC PATCH 00/11] mm/mempolicy: Make task->mempolicy externally modifiable via syscall and procfs Message-ID: References: <20231122211200.31620-1-gregory.price@memverge.com> <20231122133348.d27c09a90bce755dc1c0f251@linux-foundation.org> Precedence: bulk X-Mailing-List: linux-api@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Authentication-Results: smtp-out1.suse.de; none X-Spam-Level: X-Spam-Score: -1.10 X-Spamd-Result: default: False [-1.10 / 50.00]; ARC_NA(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; BAYES_HAM(-3.00)[100.00%]; FROM_HAS_DN(0.00)[]; TO_DN_SOME(0.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; FREEMAIL_ENVRCPT(0.00)[gmail.com]; TAGGED_RCPT(0.00)[]; MIME_GOOD(-0.10)[text/plain]; RCVD_COUNT_THREE(0.00)[3]; DKIM_SIGNED(0.00)[suse.com:s=susede1]; RCPT_COUNT_TWELVE(0.00)[19]; FUZZY_BLOCKED(0.00)[rspamd.com]; FROM_EQ_ENVFROM(0.00)[]; MIME_TRACE(0.00)[0:+]; MID_RHS_NOT_FQDN(0.50)[]; FREEMAIL_CC(0.00)[linux-foundation.org,gmail.com,kvack.org,vger.kernel.org,arndb.de,linutronix.de,kernel.org,redhat.com,alien8.de,linux.intel.com,zytor.com,intel.com]; RCVD_TLS_ALL(0.00)[]; SUSPICIOUS_RECIPS(1.50)[] Sorry, didn't have much time to do a proper review. Couple of points here at least. On Wed 22-11-23 17:24:10, Gregory Price wrote: > On Wed, Nov 22, 2023 at 01:33:48PM -0800, Andrew Morton wrote: > > On Wed, 22 Nov 2023 16:11:49 -0500 Gregory Price wrote: > > > > > The patch set changes task->mempolicy to be modifiable by tasks other > > > than just current. > > > > > > The ultimate goal is to make mempolicy more flexible and extensible, > > > such as adding interleave weights (which may need to change at runtime > > > due to hotplug events). Making mempolicy externally modifiable allows > > > for userland daemons to make runtime performance adjustments to running > > > tasks without that software needing to be made numa-aware. > > > > Please add to this [0/N] a full description of the security aspect: who > > can modify whose mempolicy, along with a full description of the > > reasoning behind this decision. > > > > Will do. For the sake of v0 for now: > > 1) the task itself (task == current) > for obvious reasons: it already can > > 2) from external interfaces: CAP_SYS_NICE Makes sense. [...] > > > 3. Add external interfaces which allow for a task mempolicy to be > > > modified by another task. This is implemented in 4 syscalls > > > and a procfs interface: > > > sys_set_task_mempolicy > > > sys_get_task_mempolicy > > > sys_set_task_mempolicy_home_node > > > sys_task_mbind > > > /proc/[pid]/mempolicy > > > > Why is the procfs interface needed? Doesn't it simply duplicate the > > syscall interface? Please update [0/N] with a description of this > > decision. > > > > Honestly I wrote the procfs interface first, and then came back around > to just implement the syscalls. mbind is not friendly to being procfs'd > so if the preference is to have only one, not both, then it should > probably be the syscalls. > > That said, when I introduce weighted interleave on top of this, having a > simple procfs interface to those weights would be valuable, so I > imagined something like `proc/mempolicy` to determine if interleave was > being used and something like `proc/mpol_interleave_weights` for a clean > interface to update weights. > > However, in the same breath, I have a prior RFC with set/get_mempolicy2 > which could probably take all future mempolicy extensions and wrap them > up into one pair of syscalls, instead of us ending up with 200 more > sys_mempolicy_whatever as memory attached fabrics become more common. > > So... yeah... the is one area I think the community very much needs to > comment: set/get_mempolicy2, many new mempolicy syscalls, procfs? All > of the above? I think we should actively avoid using proc interface. The most reasonable way would be to add get_mempolicy2 interface that would allow extensions and then create a pidfd counterpart to allow acting on a remote task. The latter would require some changes to make mempolicy code less current oriented. -- Michal Hocko SUSE Labs