From mboxrd@z Thu Jan 1 00:00:00 1970 From: mhocko@kernel.org (Michal Hocko) Date: Mon, 2 Jul 2018 15:32:47 +0200 Subject: [PATCH] mm: cma: honor __GFP_ZERO flag in cma_alloc() In-Reply-To: <20180702132335eucas1p1323fbf51cd5e82a59939d72097acee04~9kAizDyji0466904669eucas1p1w@eucas1p1.samsung.com> References: <20180613085851eucas1p20337d050face8ff8ea87674e16a9ccd2~3rI_9nj8b0455904559eucas1p2C@eucas1p2.samsung.com> <20180613122359.GA8695@bombadil.infradead.org> <20180613124001eucas1p2422f7916367ce19fecd40d6131990383~3uKFrT3ML1977219772eucas1p2G@eucas1p2.samsung.com> <20180613125546.GB32016@infradead.org> <20180613133913.GD20315@dhcp22.suse.cz> <20180702132335eucas1p1323fbf51cd5e82a59939d72097acee04~9kAizDyji0466904669eucas1p1w@eucas1p1.samsung.com> Message-ID: <20180702133247.GT19043@dhcp22.suse.cz> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Mon 02-07-18 15:23:34, Marek Szyprowski wrote: > Hi Michal, > > On 2018-06-13 15:39, Michal Hocko wrote: > > On Wed 13-06-18 05:55:46, Christoph Hellwig wrote: > >> On Wed, Jun 13, 2018 at 02:40:00PM +0200, Marek Szyprowski wrote: > >>> It is not only the matter of the spinlocks. GFP_ATOMIC is not supported > >>> by the > >>> memory compaction code, which is used in alloc_contig_range(). Right, this > >>> should be also noted in the documentation. > >> Documentation is good, asserts are better. The code should reject any > >> flag not explicitly supported, or even better have its own flags type > >> with the few actually supported flags. > > Agreed. Is the cma allocator used for anything other than GFP_KERNEL > > btw.? If not then, shouldn't we simply drop the gfp argument altogether > > rather than give users a false hope for differen gfp modes that are not > > really supported and grow broken code? > > Nope, all cma_alloc() callers are expected to use it with GFP_KERNEL gfp > mask. > The only flag which is now checked is __GFP_NOWARN. I can change the > function > signature of cma_alloc to: > struct page *cma_alloc(struct cma *cma, size_t count, unsigned int > align, bool no_warn); Are there any __GFP_NOWARN users? I have quickly hit the indirection trap and searching for alloc callback didn't tell me really much. > What about clearing the allocated buffer? Should it be another bool > parameter, done unconditionally or moved to the callers? That really depends on callers. I have no idea what they actually ask for. -- Michal Hocko SUSE Labs From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ed1-f69.google.com (mail-ed1-f69.google.com [209.85.208.69]) by kanga.kvack.org (Postfix) with ESMTP id 6AC766B0008 for ; Mon, 2 Jul 2018 09:32:51 -0400 (EDT) Received: by mail-ed1-f69.google.com with SMTP id g16-v6so5737334edq.10 for ; Mon, 02 Jul 2018 06:32:51 -0700 (PDT) Received: from mx1.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id v6-v6si301933edb.343.2018.07.02.06.32.50 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 02 Jul 2018 06:32:50 -0700 (PDT) Date: Mon, 2 Jul 2018 15:32:47 +0200 From: Michal Hocko Subject: Re: [PATCH] mm: cma: honor __GFP_ZERO flag in cma_alloc() Message-ID: <20180702133247.GT19043@dhcp22.suse.cz> References: <20180613085851eucas1p20337d050face8ff8ea87674e16a9ccd2~3rI_9nj8b0455904559eucas1p2C@eucas1p2.samsung.com> <20180613122359.GA8695@bombadil.infradead.org> <20180613124001eucas1p2422f7916367ce19fecd40d6131990383~3uKFrT3ML1977219772eucas1p2G@eucas1p2.samsung.com> <20180613125546.GB32016@infradead.org> <20180613133913.GD20315@dhcp22.suse.cz> <20180702132335eucas1p1323fbf51cd5e82a59939d72097acee04~9kAizDyji0466904669eucas1p1w@eucas1p1.samsung.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180702132335eucas1p1323fbf51cd5e82a59939d72097acee04~9kAizDyji0466904669eucas1p1w@eucas1p1.samsung.com> Sender: owner-linux-mm@kvack.org List-ID: To: Marek Szyprowski Cc: Christoph Hellwig , Matthew Wilcox , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Andrew Morton , Michal Nazarewicz , Joonsoo Kim , Vlastimil Babka On Mon 02-07-18 15:23:34, Marek Szyprowski wrote: > Hi Michal, > > On 2018-06-13 15:39, Michal Hocko wrote: > > On Wed 13-06-18 05:55:46, Christoph Hellwig wrote: > >> On Wed, Jun 13, 2018 at 02:40:00PM +0200, Marek Szyprowski wrote: > >>> It is not only the matter of the spinlocks. GFP_ATOMIC is not supported > >>> by the > >>> memory compaction code, which is used in alloc_contig_range(). Right, this > >>> should be also noted in the documentation. > >> Documentation is good, asserts are better. The code should reject any > >> flag not explicitly supported, or even better have its own flags type > >> with the few actually supported flags. > > Agreed. Is the cma allocator used for anything other than GFP_KERNEL > > btw.? If not then, shouldn't we simply drop the gfp argument altogether > > rather than give users a false hope for differen gfp modes that are not > > really supported and grow broken code? > > Nope, all cma_alloc() callers are expected to use it with GFP_KERNEL gfp > mask. > The only flag which is now checked is __GFP_NOWARN. I can change the > function > signature of cma_alloc to: > struct page *cma_alloc(struct cma *cma, size_t count, unsigned int > align, bool no_warn); Are there any __GFP_NOWARN users? I have quickly hit the indirection trap and searching for alloc callback didn't tell me really much. > What about clearing the allocated buffer? Should it be another bool > parameter, done unconditionally or moved to the callers? That really depends on callers. I have no idea what they actually ask for. -- Michal Hocko SUSE Labs