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 X-Spam-Level: X-Spam-Status: No, score=-4.0 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2BA90C433E0 for ; Tue, 11 Aug 2020 08:19:21 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id F0C18206B5 for ; Tue, 11 Aug 2020 08:19:20 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org F0C18206B5 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=suse.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 7DF8F6B0003; Tue, 11 Aug 2020 04:19:20 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 790676B0005; Tue, 11 Aug 2020 04:19:20 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 659596B0006; Tue, 11 Aug 2020 04:19:20 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0043.hostedemail.com [216.40.44.43]) by kanga.kvack.org (Postfix) with ESMTP id 507896B0003 for ; Tue, 11 Aug 2020 04:19:20 -0400 (EDT) Received: from smtpin04.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with ESMTP id E3BC3181AEF07 for ; Tue, 11 Aug 2020 08:19:19 +0000 (UTC) X-FDA: 77137588038.04.shop99_190f4d826fe1 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin04.hostedemail.com (Postfix) with ESMTP id A51D7800DDF7 for ; Tue, 11 Aug 2020 08:19:19 +0000 (UTC) X-HE-Tag: shop99_190f4d826fe1 X-Filterd-Recvd-Size: 2893 Received: from mx2.suse.de (mx2.suse.de [195.135.220.15]) by imf24.hostedemail.com (Postfix) with ESMTP for ; Tue, 11 Aug 2020 08:19:19 +0000 (UTC) X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 93D56AB8B; Tue, 11 Aug 2020 08:19:38 +0000 (UTC) Date: Tue, 11 Aug 2020 10:19:17 +0200 From: Michal Hocko To: Uladzislau Rezki Cc: LKML , RCU , linux-mm@kvack.org, Andrew Morton , Vlastimil Babka , "Paul E . McKenney" , Matthew Wilcox , "Theodore Y . Ts'o" , Joel Fernandes , Sebastian Andrzej Siewior , Oleksiy Avramchenko Subject: Re: [RFC-PATCH 1/2] mm: Add __GFP_NO_LOCKS flag Message-ID: <20200811081917.GG4793@dhcp22.suse.cz> References: <20200809204354.20137-1-urezki@gmail.com> <20200809204354.20137-2-urezki@gmail.com> <20200810123141.GF4773@dhcp22.suse.cz> <20200810160739.GA29884@pc636> <20200810192525.GG4773@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200810192525.GG4773@dhcp22.suse.cz> X-Rspamd-Queue-Id: A51D7800DDF7 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam05 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon 10-08-20 21:25:26, Michal Hocko wrote: > On Mon 10-08-20 18:07:39, Uladzislau Rezki wrote: [...] > > The problem that i see is we can not use the page allocator from atomic > > contexts, what is our case: > > > > > > local_irq_save(flags) or preempt_disable() or raw_spinlock(); > > __get_free_page(GFP_ATOMIC); > > > > > > So if we can convert the page allocator to raw_* lock it will be appreciated, > > at least from our side, IMHO, not from RT one. But as i stated above we need > > to sort raised questions out if converting is done. > > > > What is your view? > > To me it would make more sense to support atomic allocations also for > the RT tree. Having both GFP_NOWAIT and GFP_ATOMIC which do not really > work for atomic context in RT sounds subtle and wrong. I was thinking about this some more. I still think the above would be a reasonable goal we should try to achieve. If for not other then for future maintainability (especially after the RT patchset is merged). I have tried to search for any known problems/attempts to make zone->lock raw but couldn't find anything. Maybe somebody more involved in RT world have something to say about that. Anyway, if the zone->lock is not a good fit for raw_spin_lock then the only way I can see forward is to detect real (RT) atomic contexts and bail out early before taking the lock in the allocator for NOWAIT/ATOMIC requests. -- Michal Hocko SUSE Labs