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=-1.0 required=3.0 tests=MAILING_LIST_MULTI,SPF_PASS autolearn=ham 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 76565C433EF for ; Tue, 19 Jun 2018 10:43:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 315082083D for ; Tue, 19 Jun 2018 10:43:19 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 315082083D Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S966136AbeFSKnR (ORCPT ); Tue, 19 Jun 2018 06:43:17 -0400 Received: from mx2.suse.de ([195.135.220.15]:54195 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965187AbeFSKnO (ORCPT ); Tue, 19 Jun 2018 06:43:14 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (charybdis-ext-too.suse.de [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id 9E609ABF4; Tue, 19 Jun 2018 10:43:12 +0000 (UTC) Date: Tue, 19 Jun 2018 12:43:12 +0200 From: Michal Hocko To: Mikulas Patocka Cc: jing xia , Mike Snitzer , agk@redhat.com, dm-devel@redhat.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: dm bufio: Reduce dm_bufio_lock contention Message-ID: <20180619104312.GD13685@dhcp22.suse.cz> References: <20180614073153.GB9371@dhcp22.suse.cz> <20180615073201.GB24039@dhcp22.suse.cz> <20180615115547.GH24039@dhcp22.suse.cz> <20180615130925.GI24039@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.5 (2018-04-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon 18-06-18 18:11:26, Mikulas Patocka wrote: [...] > I grepped the kernel for __GFP_NORETRY and triaged them. I found 16 cases > without a fallback - those are bugs that make various functions randomly > return -ENOMEM. Well, maybe those are just optimistic attempts to allocate memory and have a fallback somewhere else. So I would be careful calling them outright bugs. But maybe you are right. > Most of the callers provide callback. > > There is another strange flag - __GFP_RETRY_MAYFAIL - it provides two > different functions - if the allocation is larger than > PAGE_ALLOC_COSTLY_ORDER, it retries the allocation as if it were smaller. > If the allocations is smaller than PAGE_ALLOC_COSTLY_ORDER, > __GFP_RETRY_MAYFAIL will avoid the oom killer (larger order allocations > don't trigger the oom killer at all). Well, the primary purpose of this flag is to provide a consistent failure behavior for all requests regardless of the size. > So, perhaps __GFP_RETRY_MAYFAIL could be used instead of __GFP_NORETRY in > the cases where the caller wants to avoid trigerring the oom killer (the > problem is that __GFP_NORETRY causes random failure even in no-oom > situations but __GFP_RETRY_MAYFAIL doesn't). myabe yes. > So my suggestion is - fix these obvious bugs when someone allocates memory > with __GFP_NORETRY without any fallback - and then, __GFP_NORETRY could be > just changed to return NULL instead of sleeping. No real objection to fixing wrong __GFP_NORETRY usage. But __GFP_NORETRY can sleep. Nothing will really change in that regards. It does a reclaim and that _might_ sleep. But seriously, isn't the best way around the throttling issue to use PF_LESS_THROTTLE? -- Michal Hocko SUSE Labs