From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751291AbdAPVVR (ORCPT ); Mon, 16 Jan 2017 16:21:17 -0500 Received: from hqemgate15.nvidia.com ([216.228.121.64]:4850 "EHLO hqemgate15.nvidia.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750863AbdAPVVP (ORCPT ); Mon, 16 Jan 2017 16:21:15 -0500 X-PGP-Universal: processed; by hqnvupgp07.nvidia.com on Mon, 16 Jan 2017 01:10:47 -0800 Subject: Re: [PATCH 1/6] mm: introduce kv[mz]alloc helpers To: Michal Hocko References: <20170112153717.28943-1-mhocko@kernel.org> <20170112153717.28943-2-mhocko@kernel.org> <20170116084717.GA13641@dhcp22.suse.cz> <0ca8a212-c651-7915-af25-23925e1c1cc3@nvidia.com> <20170116194052.GA9382@dhcp22.suse.cz> CC: Andrew Morton , Vlastimil Babka , David Rientjes , Mel Gorman , Johannes Weiner , Al Viro , , LKML , Anatoly Stepanov , Paolo Bonzini , Mike Snitzer , "Michael S. Tsirkin" , "Theodore Ts'o" X-Nvconfidentiality: public From: John Hubbard Message-ID: <1979f5e1-a335-65d8-8f9a-0aef17898ca1@nvidia.com> Date: Mon, 16 Jan 2017 13:15:08 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.6.0 MIME-Version: 1.0 In-Reply-To: <20170116194052.GA9382@dhcp22.suse.cz> X-Originating-IP: [172.17.160.221] X-ClientProxiedBy: HQMAIL103.nvidia.com (172.20.187.11) To HQMAIL107.nvidia.com (172.20.187.13) Content-Type: text/plain; charset="windows-1252"; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 01/16/2017 11:40 AM, Michal Hocko wrote: > On Mon 16-01-17 11:09:37, John Hubbard wrote: >> >> >> On 01/16/2017 12:47 AM, Michal Hocko wrote: >>> On Sun 15-01-17 20:34:13, John Hubbard wrote: > [...] >>>> Is that "Reclaim modifiers" line still true, or is it a leftover from an >>>> earlier approach? I am having trouble reconciling it with rest of the >>>> patchset, because: >>>> >>>> a) the flags argument below is effectively passed on to either kmalloc_node >>>> (possibly adding, but not removing flags), or to __vmalloc_node_flags. >>> >>> The above only says thos are _unsupported_ - in other words the behavior >>> is not defined. Even if flags are passed down to kmalloc resp. vmalloc >>> it doesn't mean they are used that way. Remember that vmalloc uses >>> some hardcoded GFP_KERNEL allocations. So while I could be really >>> strict about this and mask away these flags I doubt this is worth the >>> additional code. >> >> I do wonder about passing those flags through to kmalloc. Maybe it is worth >> stripping out __GFP_NORETRY and __GFP_NOFAIL, after all. It provides some >> insulation from any future changes to the implementation of kmalloc, and it >> also makes the documentation more believable. > > I am not really convinced that we should take an extra steps for these > flags. There are no existing users for those flags and new users should > follow the documentation. OK, let's just fortify the documentation ever so slightly, then, so that users are more likely to do the right thing. How's this sound: * Reclaim modifiers - __GFP_NORETRY and __GFP_NOFAIL are not supported. (Even * though the current implementation passes the flags on through to kmalloc and * vmalloc, that is done for efficiency and to avoid unnecessary code. The caller * should not pass in these flags.) * * __GFP_REPEAT is supported, but only for large (>64kB) allocations. ? Or is that documentation overkill? thanks john h > > -- > Michal Hocko > SUSE Labs > From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f199.google.com (mail-pf0-f199.google.com [209.85.192.199]) by kanga.kvack.org (Postfix) with ESMTP id 4C9BE6B0033 for ; Mon, 16 Jan 2017 16:15:11 -0500 (EST) Received: by mail-pf0-f199.google.com with SMTP id 80so265131218pfy.2 for ; Mon, 16 Jan 2017 13:15:11 -0800 (PST) Received: from hqemgate15.nvidia.com (hqemgate15.nvidia.com. [216.228.121.64]) by mx.google.com with ESMTPS id n22si22637033pfj.253.2017.01.16.13.15.10 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 16 Jan 2017 13:15:10 -0800 (PST) Subject: Re: [PATCH 1/6] mm: introduce kv[mz]alloc helpers References: <20170112153717.28943-1-mhocko@kernel.org> <20170112153717.28943-2-mhocko@kernel.org> <20170116084717.GA13641@dhcp22.suse.cz> <0ca8a212-c651-7915-af25-23925e1c1cc3@nvidia.com> <20170116194052.GA9382@dhcp22.suse.cz> From: John Hubbard Message-ID: <1979f5e1-a335-65d8-8f9a-0aef17898ca1@nvidia.com> Date: Mon, 16 Jan 2017 13:15:08 -0800 MIME-Version: 1.0 In-Reply-To: <20170116194052.GA9382@dhcp22.suse.cz> Content-Type: text/plain; charset="windows-1252"; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: Andrew Morton , Vlastimil Babka , David Rientjes , Mel Gorman , Johannes Weiner , Al Viro , linux-mm@kvack.org, LKML , Anatoly Stepanov , Paolo Bonzini , Mike Snitzer , "Michael S. Tsirkin" , Theodore Ts'o On 01/16/2017 11:40 AM, Michal Hocko wrote: > On Mon 16-01-17 11:09:37, John Hubbard wrote: >> >> >> On 01/16/2017 12:47 AM, Michal Hocko wrote: >>> On Sun 15-01-17 20:34:13, John Hubbard wrote: > [...] >>>> Is that "Reclaim modifiers" line still true, or is it a leftover from an >>>> earlier approach? I am having trouble reconciling it with rest of the >>>> patchset, because: >>>> >>>> a) the flags argument below is effectively passed on to either kmalloc_node >>>> (possibly adding, but not removing flags), or to __vmalloc_node_flags. >>> >>> The above only says thos are _unsupported_ - in other words the behavior >>> is not defined. Even if flags are passed down to kmalloc resp. vmalloc >>> it doesn't mean they are used that way. Remember that vmalloc uses >>> some hardcoded GFP_KERNEL allocations. So while I could be really >>> strict about this and mask away these flags I doubt this is worth the >>> additional code. >> >> I do wonder about passing those flags through to kmalloc. Maybe it is worth >> stripping out __GFP_NORETRY and __GFP_NOFAIL, after all. It provides some >> insulation from any future changes to the implementation of kmalloc, and it >> also makes the documentation more believable. > > I am not really convinced that we should take an extra steps for these > flags. There are no existing users for those flags and new users should > follow the documentation. OK, let's just fortify the documentation ever so slightly, then, so that users are more likely to do the right thing. How's this sound: * Reclaim modifiers - __GFP_NORETRY and __GFP_NOFAIL are not supported. (Even * though the current implementation passes the flags on through to kmalloc and * vmalloc, that is done for efficiency and to avoid unnecessary code. The caller * should not pass in these flags.) * * __GFP_REPEAT is supported, but only for large (>64kB) allocations. ? Or is that documentation overkill? thanks john h > > -- > 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