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Mon, 29 Mar 2021 22:27:03 +0000 Subject: Re: [PATCH 1/8] mm: cma: introduce cma_release_nowait() To: Michal Hocko Cc: Roman Gushchin , Minchan Kim , David Hildenbrand , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Shakeel Butt , Oscar Salvador , Muchun Song , David Rientjes , Miaohe Lin , Peter Zijlstra , Matthew Wilcox , HORIGUCHI NAOYA , "Aneesh Kumar K . V" , Waiman Long , Peter Xu , Mina Almasry , Hillf Danton , Andrew Morton , Joonsoo Kim , Barry Song , Will Deacon References: <20210325002835.216118-1-mike.kravetz@oracle.com> <20210325002835.216118-2-mike.kravetz@oracle.com> <76aaf359-9496-04df-a585-3662d0375749@oracle.com> <4bc3c5d8-f1a7-6439-8fee-582364a7c021@redhat.com> <0f7f3c4e-530a-5cd2-2719-259e509366e4@oracle.com> From: Mike Kravetz Message-ID: <0b2afe77-f7fb-4c44-2861-bdf4085fe9e8@oracle.com> Date: Mon, 29 Mar 2021 15:27:00 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.1.1 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [50.38.35.18] X-ClientProxiedBy: CO2PR04CA0173.namprd04.prod.outlook.com (2603:10b6:104:4::27) To BY5PR10MB4196.namprd10.prod.outlook.com (2603:10b6:a03:20d::23) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from [192.168.2.112] (50.38.35.18) by CO2PR04CA0173.namprd04.prod.outlook.com (2603:10b6:104:4::27) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3977.24 via Frontend Transport; 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identity=mailfrom; envelope-from=""; helo=userp2130.oracle.com; client-ip=156.151.31.86 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1617056885-117790 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 3/29/21 12:46 AM, Michal Hocko wrote: > On Fri 26-03-21 14:32:01, Mike Kravetz wrote: > [...] >> - Just change the mutex to an irq safe spinlock. > > Yes please. > >> AFAICT, the potential >> downsides could be: >> - Interrupts disabled during long bitmap scans > > How large those bitmaps are in practice? > >> - Wasted cpu cycles (spinning) if there is much contention on lock >> Both of these would be more of an issue on small/embedded systems. I >> took a quick look at the callers of cma_alloc/cma_release and nothing >> stood out that could lead to high degrees of contention. However, I >> could have missed something. > > If this is really a practical concern then we can try a more complex > solution based on some data. > Ok, I will send v2 with this approach. Adding Barry and Will on Cc: as they were involved in adding more cma use cases for dma on arm. -- Mike Kravetz