From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wr0-f197.google.com (mail-wr0-f197.google.com [209.85.128.197]) by kanga.kvack.org (Postfix) with ESMTP id 35D646B0007 for ; Tue, 19 Jun 2018 06:43:14 -0400 (EDT) Received: by mail-wr0-f197.google.com with SMTP id x6-v6so13831709wrl.6 for ; Tue, 19 Jun 2018 03:43:14 -0700 (PDT) Received: from mx2.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id g10-v6si8732407edf.328.2018.06.19.03.43.12 for (version=TLS1 cipher=AES128-SHA bits=128/128); Tue, 19 Jun 2018 03:43:13 -0700 (PDT) Date: Tue, 19 Jun 2018 12:43:12 +0200 From: Michal Hocko 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: Sender: owner-linux-mm@kvack.org List-ID: To: Mikulas Patocka Cc: jing xia , Mike Snitzer , agk@redhat.com, dm-devel@redhat.com, linux-kernel@vger.kernel.org, linux-mm@kvack.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