Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751359AbdHaLfc (ORCPT ); Thu, 31 Aug 2017 07:35:32 -0400 Received: from mx2.suse.de ([195.135.220.15]:56414 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751250AbdHaLf2 (ORCPT ); Thu, 31 Aug 2017 07:35:28 -0400 Subject: Re: [PATCH 1/3] mm/cma: manage the memory of the CMA area by using the ZONE_MOVABLE To: Joonsoo Kim Cc: Andrew Morton , Rik van Riel , Johannes Weiner , mgorman@techsingularity.net, Laura Abbott , Minchan Kim , Marek Szyprowski , Michal Nazarewicz , "Aneesh Kumar K . V" , Russell King , Will Deacon , linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@lge.com, Kees Cook References: <1503556593-10720-1-git-send-email-iamjoonsoo.kim@lge.com> <1503556593-10720-2-git-send-email-iamjoonsoo.kim@lge.com> <20170831014048.GA24271@js1304-P5Q-DELUXE> From: Vlastimil Babka Message-ID: Date: Thu, 31 Aug 2017 13:32:12 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.3.0 MIME-Version: 1.0 In-Reply-To: <20170831014048.GA24271@js1304-P5Q-DELUXE> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2829 Lines: 73 On 08/31/2017 03:40 AM, Joonsoo Kim wrote: > On Tue, Aug 29, 2017 at 11:16:18AM +0200, Vlastimil Babka wrote: >> On 08/24/2017 08:36 AM, js1304@gmail.com wrote: >>> From: Joonsoo Kim >>> >>> 0. History >>> >>> This patchset is the follow-up of the discussion about the >>> "Introduce ZONE_CMA (v7)" [1]. Please reference it if more information >>> is needed. >>> >> >> [...] >> >>> >>> [1]: lkml.kernel.org/r/1491880640-9944-1-git-send-email-iamjoonsoo.kim@lge.com >>> [2]: https://lkml.org/lkml/2014/10/15/623 >>> [3]: http://www.spinics.net/lists/linux-mm/msg100562.html >>> >>> Reviewed-by: Aneesh Kumar K.V >>> Acked-by: Vlastimil Babka >> >> The previous version has introduced ZONE_CMA, so I would think switching >> to ZONE_MOVABLE is enough to drop previous reviews. Perhaps most of the >> code involved is basically the same, though? > > Yes, most of the code involved is the same. I considered to drop > previous review tags but most of the code and concept is the same so I > decide to keep review tags. I should mention it in cover-letter but I > forgot to mention it. Sorry about that. > >> Anyway I checked the current patch and did some basic tests with qemu, >> so you can keep my ack. > > Thanks! > >> >> BTW, if we dropped NR_FREE_CMA_PAGES, could we also drop MIGRATE_CMA and >> related hooks? Is that counter really that useful as it works right now? >> It will decrease both by CMA allocations (which has to be explicitly >> freed) and by movable allocations (which can be migrated). What if only >> CMA alloc/release touched it? > > I think that NR_FREE_CMA_PAGES would not be as useful as previous. We > can remove it. > > However, removing MIGRATE_CMA has a problem. There is an usecase to > check if the page comes from the CMA area or not. See > check_page_span() in mm/usercopy.c. I can implement it differently by > iterating whole CMA area and finding the match, but I'm not sure it's > performance effect. I guess that it would be marginal. +CC Kees Cook Hmm, seems like this check is to make sure we don't copy from/to parts of kernel memory we're not supposed to? Then I believe checking that pages are in ZONE_MOVABLE should then give the same guarantees as MIGRATE_CMA. BTW the comment says "Reject if range is entirely either Reserved or CMA" but the code does the opposite thing. I assume the comment is wrong? > Anyway, I'd like not to cause any side-effect now. After patches are > settle down on mainline, I will try to remove them as you suggested. > > Thanks. > > -- > 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 >