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Tue, 17 Aug 2021 00:58:33 +0000 Received: from BY5PR10MB4196.namprd10.prod.outlook.com ([fe80::8d2a:558d:ab4a:9c2a]) by BY5PR10MB4196.namprd10.prod.outlook.com ([fe80::8d2a:558d:ab4a:9c2a%7]) with mapi id 15.20.4415.023; Tue, 17 Aug 2021 00:58:33 +0000 Subject: Re: [PATCH RESEND 0/8] hugetlb: add demote/split page functionality To: Andrew Morton Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, David Hildenbrand , Michal Hocko , Oscar Salvador , Zi Yan , Muchun Song , Naoya Horiguchi , David Rientjes References: <20210816224953.157796-1-mike.kravetz@oracle.com> <20210816162305.b19bfa3f3ba7431a62ff205f@linux-foundation.org> <5dd4e07b-d2cf-63f2-fc0a-9b371b469a44@oracle.com> <20210816173959.950443c7516a2b178e2ec376@linux-foundation.org> From: Mike Kravetz Message-ID: <54fdf347-e12e-0d3e-6c33-8b1b7898876c@oracle.com> Date: Mon, 16 Aug 2021 17:58:31 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.1.1 In-Reply-To: <20210816173959.950443c7516a2b178e2ec376@linux-foundation.org> Content-Type: text/plain; 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dkim=pass header.d=oracle.com header.s=corp-2021-07-09 header.b=lSo9LkbG; dkim=pass header.d=oracle.com header.s=corp-2020-01-29 header.b=AjR2cjig; dkim=pass header.d=oracle.onmicrosoft.com header.s=selector2-oracle-onmicrosoft-com header.b="TxyKOgo/"; dmarc=pass (policy=none) header.from=oracle.com; spf=none (imf27.hostedemail.com: domain of mike.kravetz@oracle.com has no SPF policy when checking 205.220.165.32) smtp.mailfrom=mike.kravetz@oracle.com X-HE-Tag: 1629161922-545668 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 8/16/21 5:39 PM, Andrew Morton wrote: > On Mon, 16 Aug 2021 17:17:50 -0700 Mike Kravetz wrote: > >>> >>> And how does one know the operation has completed so the sysfs files >>> can be reloaded for another operation? >>> >> >> When the write to the file is complete, the operation has completed. >> Not exactly sure what you mean by reloading the sysfs files for >> another operation? > > If userspace wishes to perform another demote operation, it must wait > for the preceding one to complete. > > Presumably if thread A is blocked in a write to `demote' and thread B > concurrently tries to perform a demotion, thread B will be blocked as > well? Was this tested? I must admit that I did not specifically test this. However, the patch series to make freeing of hugetlb pages IRQ safe added a (per-hstate)mutex that is taken when sysfs files modify the number of huge pages. demote writes take this mutex (patch 1). That synchronizes not only concurrent writes to demote but also concurrent modifications of nr_hugepages. > > Lots of things are to be added to changelogs & documentation, methinks. > OK. Thank you for taking a look at this! -- Mike Kravetz