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Tue, 23 Mar 2021 18:51:09 +0000 Subject: Re: [RFC PATCH 7/8] hugetlb: add update_and_free_page_no_sleep for irq context To: Roman Gushchin Cc: Peter Zijlstra , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Michal Hocko , Shakeel Butt , Oscar Salvador , David Hildenbrand , Muchun Song , David Rientjes , Miaohe Lin , Matthew Wilcox , HORIGUCHI NAOYA , "Aneesh Kumar K . V" , Waiman Long , Peter Xu , Mina Almasry , Andrew Morton , Christoph Hellwig References: <20210319224209.150047-1-mike.kravetz@oracle.com> <20210319224209.150047-8-mike.kravetz@oracle.com> <2383057a-29dc-383b-720f-7cdcdd015e40@oracle.com> From: Mike Kravetz Message-ID: <8a28c691-1e7c-1463-9d59-da31a2926adc@oracle.com> Date: Tue, 23 Mar 2021 11:51:04 -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: MWHPR15CA0066.namprd15.prod.outlook.com (2603:10b6:301:4c::28) 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 MWHPR15CA0066.namprd15.prod.outlook.com (2603:10b6:301:4c::28) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3955.18 via Frontend Transport; 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identity=mailfrom; envelope-from=""; helo=aserp2130.oracle.com; client-ip=141.146.126.79 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1616525490-199233 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 3/22/21 11:10 AM, Roman Gushchin wrote: > On Mon, Mar 22, 2021 at 10:42:23AM -0700, Mike Kravetz wrote: >> Cc: Roman, Christoph >> >> On 3/22/21 1:41 AM, Peter Zijlstra wrote: >>> On Fri, Mar 19, 2021 at 03:42:08PM -0700, Mike Kravetz wrote: >>>> The locks acquired in free_huge_page are irq safe. However, in certain >>>> circumstances the routine update_and_free_page could sleep. Since >>>> free_huge_page can be called from any context, it can not sleep. >>>> >>>> Use a waitqueue to defer freeing of pages if the operation may sleep. A >>>> new routine update_and_free_page_no_sleep provides this functionality >>>> and is only called from free_huge_page. >>>> >>>> Note that any 'pages' sent to the workqueue for deferred freeing have >>>> already been removed from the hugetlb subsystem. What is actually >>>> deferred is returning those base pages to the low level allocator. >>> >>> So maybe I'm stupid, but why do you need that work in hugetlb? Afaict it >>> should be in cma_release(). >> >> My thinking (which could be totally wrong) is that cma_release makes no >> claims about calling context. From the code, it is pretty clear that it >> can only be called from task context with no locks held. Although, >> there could be code incorrectly calling it today hugetlb does. Since >> hugetlb is the only code with this new requirement, it should do the >> work. >> >> Wait!!! That made me remember something. >> Roman had code to create a non-blocking version of cma_release(). >> https://lore.kernel.org/linux-mm/20201022225308.2927890-1-guro@fb.com/ >> >> There were no objections, and Christoph even thought there may be >> problems with callers of dma_free_contiguous. >> >> Perhaps, we should just move forward with Roman's patches to create >> cma_release_nowait() and avoid this workqueue stuff? > > Sounds good to me. If it's the preferred path, I can rebase and resend > those patches (they been carried for some time by Zi Yan for his 1GB THP work, > but they are completely independent). Thanks Roman, Yes, this is the preferred path. If there is a non blocking version of cma_release, then it makes fixup of hugetlb put_page path much easier. If you would prefer, I can rebase your patches and send with this series. -- Mike Kravetz