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=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 9D2D0C433E0 for ; Mon, 15 Feb 2021 19:03:15 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 1CDDC64E0F for ; Mon, 15 Feb 2021 19:03:15 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 1CDDC64E0F Authentication-Results: mail.kernel.org; dmarc=fail (p=quarantine 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 558D78D0138; Mon, 15 Feb 2021 14:03:14 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 508C88D012C; Mon, 15 Feb 2021 14:03:14 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 3D0C68D0138; Mon, 15 Feb 2021 14:03:14 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0004.hostedemail.com [216.40.44.4]) by kanga.kvack.org (Postfix) with ESMTP id 26A7A8D012C for ; Mon, 15 Feb 2021 14:03:14 -0500 (EST) Received: from smtpin25.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id E32816C16 for ; Mon, 15 Feb 2021 19:03:13 +0000 (UTC) X-FDA: 77821425066.25.cry15_470380c2763d Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin25.hostedemail.com (Postfix) with ESMTP id D22851812A464 for ; Mon, 15 Feb 2021 19:03:13 +0000 (UTC) X-HE-Tag: cry15_470380c2763d X-Filterd-Recvd-Size: 5606 Received: from mx2.suse.de (mx2.suse.de [195.135.220.15]) by imf01.hostedemail.com (Postfix) with ESMTP for ; Mon, 15 Feb 2021 19:03:13 +0000 (UTC) X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1613415792; 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=+fd7ihZjbhcZ8UUvdOazTdIjmKtVbqj7x1WqiHSTYpo=; b=PWlJyJF9epJo/+kqbywJfNJKobXG+JhtYEtY1HliEUOiac+chaXYl2jiGSBLMu7eV4qsCa oxm2AsOwKtBTAcXzOj2fFapPWffqp3ihTo3iFgaLcpwm1sYA2IAjf/3Fc8imYtbLQekL7R CF282g/eNl+JimV7h/fWNdWrWJpxnGY= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id DBB47ACD4; Mon, 15 Feb 2021 19:03:11 +0000 (UTC) Date: Mon, 15 Feb 2021 20:02:59 +0100 From: Michal Hocko To: Muchun Song Cc: Jonathan Corbet , Mike Kravetz , Thomas Gleixner , mingo@redhat.com, bp@alien8.de, x86@kernel.org, hpa@zytor.com, dave.hansen@linux.intel.com, luto@kernel.org, Peter Zijlstra , viro@zeniv.linux.org.uk, Andrew Morton , paulmck@kernel.org, mchehab+huawei@kernel.org, pawan.kumar.gupta@linux.intel.com, Randy Dunlap , oneukum@suse.com, anshuman.khandual@arm.com, jroedel@suse.de, Mina Almasry , David Rientjes , Matthew Wilcox , Oscar Salvador , "Song Bao Hua (Barry Song)" , David Hildenbrand , HORIGUCHI =?utf-8?B?TkFPWUEo5aCA5Y+jIOebtOS5nyk=?= , Joao Martins , Xiongchun duan , linux-doc@vger.kernel.org, LKML , Linux Memory Management List , linux-fsdevel Subject: Re: [External] Re: [PATCH v15 4/8] mm: hugetlb: alloc the vmemmap pages associated with each HugeTLB page Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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 Tue 16-02-21 01:48:29, Muchun Song wrote: > On Tue, Feb 16, 2021 at 12:28 AM Michal Hocko wrote: > > > > On Mon 15-02-21 23:36:49, Muchun Song wrote: > > [...] > > > > There shouldn't be any real reason why the memory allocation for > > > > vmemmaps, or handling vmemmap in general, has to be done from within the > > > > hugetlb lock and therefore requiring a non-sleeping semantic. All that > > > > can be deferred to a more relaxed context. If you want to make a > > > > > > Yeah, you are right. We can put the freeing hugetlb routine to a > > > workqueue. Just like I do in the previous version (before v13) patch. > > > I will pick up these patches. > > > > I haven't seen your v13 and I will unlikely have time to revisit that > > version. I just wanted to point out that the actual allocation doesn't > > have to happen from under the spinlock. There are multiple ways to go > > around that. Dropping the lock would be one of them. Preallocation > > before the spin lock is taken is another. WQ is certainly an option but > > I would take it as the last resort when other paths are not feasible. > > > > "Dropping the lock" and "Preallocation before the spin lock" can limit > the context of put_page to non-atomic context. I am not sure if there > is a page puted somewhere under an atomic context. e.g. compaction. > I am not an expert on this. Then do a due research or ask for a help from the MM community. Do not just try to go around harder problems and somehow duct tape a solution. I am sorry for sounding harsh here but this is a repetitive pattern. Now to the merit. put_page can indeed be called from all sorts of contexts. And it might be indeed impossible to guarantee that hugetlb pages are never freed up from an atomic context. Requiring that would be even hard to maintain longterm. There are ways around that, I believe, though. The most simple one that I can think of right now would be using in_atomic() rather than in_task() check free_huge_page. IIRC recent changes would allow in_atomic to be reliable also on !PREEMPT kernels (via RCU tree, not sure where this stands right now). That would make __free_huge_page always run in a non-atomic context which sounds like an easy enough solution. Another way would be to keep a pool of ready pages to use in case of GFP_NOWAIT allocation fails and have means to keep that pool replenished when needed. Would it be feasible to reused parts of the freed page in the worst case? -- Michal Hocko SUSE Labs