From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-lf0-f70.google.com (mail-lf0-f70.google.com [209.85.215.70]) by kanga.kvack.org (Postfix) with ESMTP id 7A15F6B007E for ; Thu, 2 Jun 2016 02:32:34 -0400 (EDT) Received: by mail-lf0-f70.google.com with SMTP id o70so19542130lfg.1 for ; Wed, 01 Jun 2016 23:32:34 -0700 (PDT) Received: from mail-wm0-f66.google.com (mail-wm0-f66.google.com. [74.125.82.66]) by mx.google.com with ESMTPS id f5si61617496wje.247.2016.06.01.23.32.33 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 01 Jun 2016 23:32:33 -0700 (PDT) Received: by mail-wm0-f66.google.com with SMTP id a20so1320894wma.3 for ; Wed, 01 Jun 2016 23:32:33 -0700 (PDT) Date: Thu, 2 Jun 2016 08:32:31 +0200 From: Michal Hocko Subject: Re: [PATCH 04/17] arm: get rid of superfluous __GFP_REPEAT Message-ID: <20160602063231.GB1995@dhcp22.suse.cz> References: <1464599699-30131-1-git-send-email-mhocko@kernel.org> <1464599699-30131-5-git-send-email-mhocko@kernel.org> <20160601162424.GD19428@n2100.arm.linux.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160601162424.GD19428@n2100.arm.linux.org.uk> Sender: owner-linux-mm@kvack.org List-ID: To: Russell King - ARM Linux Cc: Andrew Morton , linux-mm@kvack.org, LKML , linux-arch@vger.kernel.org On Wed 01-06-16 17:24:24, Russell King - ARM Linux wrote: > On Mon, May 30, 2016 at 11:14:46AM +0200, Michal Hocko wrote: > > From: Michal Hocko > > > > __GFP_REPEAT has a rather weak semantic but since it has been introduced > > around 2.6.12 it has been ignored for low order allocations. > > > > PGALLOC_GFP uses __GFP_REPEAT but none of the allocation which uses > > this flag is for more than order-2. This means that this flag has never > > been actually useful here because it has always been used only for > > PAGE_ALLOC_COSTLY requests. > > I hear what you say, but... > > commit 8c65da6dc89ccb605d73773b1dd617e72982d971 > Author: Russell King > Date: Sat Nov 30 12:52:31 2013 +0000 > > ARM: pgd allocation: retry on failure > > Make pgd allocation retry on failure; we really need this to succeed > otherwise fork() can trigger OOMs. > > Signed-off-by: Russell King > > and that's the change which introduced this, and it did solve a problem > for me. So I'm not happy to give an ack for this change unless someone > can tell me why adding __GFP_REPEAT back then had a beneficial effect. > Maybe there was some other bug in the MM layer in 2013 which this change > happened to solve? This is hard to tell but from the code snippet I have referenced it should be pretty clear that the low order really had a nofail semantic. git grep GFP_REPEAT 8c65da6dc89ccb605d73773b1dd617e72982d971 -- mm confirms the story. Do you remember your reproducer? -- Michal Hocko SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org