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="S6QcIWw/" Received: from smtp-out1.suse.de (smtp-out1.suse.de [195.135.223.130]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C3CE21B9; Tue, 28 Nov 2023 01:45:08 -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 3F8582195A; Tue, 28 Nov 2023 09:45:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1701164707; 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=PjmgV8c/dSvki9BoDbxFb8rn9kuThbhs3kZKihqd5Ms=; b=S6QcIWw/2fwQUd4Pv6miut4WGF6hKhISBRs6Ksh/ByqrsatBI0+AGVKiQCo+GH2AOSdThy zFkQGmtFlU1Kut3woNmZDBEzD3VrwXnCutMD+gJ5wUyKVJeKq5s0IUuHBoJYtZWcF5x+76 XLaCQfYWFWo/VV4/ze4WLkQNNINejQg= 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 1B83E1343E; Tue, 28 Nov 2023 09:45:07 +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 jw6vA6O2ZWVrZAAAD6G6ig (envelope-from ); Tue, 28 Nov 2023 09:45:07 +0000 Date: Tue, 28 Nov 2023 10:45:02 +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: -6.10 X-Spamd-Result: default: False [-6.10 / 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]; REPLY(-4.00)[]; NEURAL_HAM_LONG(-1.00)[-1.000]; 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)[] On Mon 27-11-23 11:14:44, Gregory Price wrote: > On Mon, Nov 27, 2023 at 04:29:56PM +0100, Michal Hocko wrote: > > Sorry, didn't have much time to do a proper review. Couple of points > > here at least. > > > > > > > > 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. > > Sounds good, I'll pull my get/set_mempolicy2 RFC on top of this. > > Just context: patches 1-6 refactor mempolicy to allow remote task > twiddling (fixing the current-oriented issues), and patch 7 adds the pidfd > interfaces you describe above. > > > Couple Questions > > 1) Should we consider simply adding a pidfd arg to set/get_mempolicy2, > where if (pidfd == 0), then it operates on current, otherwise it > operates on the target task? That would mitigate the need for what > amounts to the exact same interface. This wouldn't fit into existing pidfd interfaces I am aware of. We assume pidfd to be real fd, no special cases. > 2) Should we combine all the existing operations into set_mempolicy2 and > add an operation arg. > > set_mempolicy2(pidfd, arg_struct, len) > > struct { > int pidfd; /* optional */ > int operation; /* describe which op_args to use */ > union { > struct { > } set_mempolicy; > struct { > } set_vma_home_node; > struct { > } mbind; > ... > } op_args; > } args; > > capturing: > sys_set_mempolicy > sys_set_mempolicy_home_node > sys_mbind > > or should we just make a separate interface for mbind/home_node to > limit complexity of the single syscall? My preference would be to go with specific syscalls. Multiplexing syscalls have turned much more complex and less flexible over time. Just have a look at futex. -- Michal Hocko SUSE Labs