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Mon, 8 Mar 2021 18:58:13 +0000 X-MS-Exchange-Authentication-Results: spf=pass (sender IP is 216.228.112.34) smtp.mailfrom=nvidia.com; linux-foundation.org; dkim=none (message not signed) header.d=none;linux-foundation.org; dmarc=pass action=none header.from=nvidia.com; Received-SPF: Pass (protection.outlook.com: domain of nvidia.com designates 216.228.112.34 as permitted sender) receiver=protection.outlook.com; client-ip=216.228.112.34; helo=mail.nvidia.com; Received: from mail.nvidia.com (216.228.112.34) by CO1NAM11FT045.mail.protection.outlook.com (10.13.175.181) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384) id 15.20.3912.17 via Frontend Transport; Mon, 8 Mar 2021 18:58:12 +0000 Received: from rcampbell-test.nvidia.com (172.20.145.6) by HQMAIL107.nvidia.com (172.20.187.13) with Microsoft SMTP Server (TLS) id 15.0.1497.2; Mon, 8 Mar 2021 18:58:12 +0000 Subject: Re: [PATCH v4 4/8] mm/rmap: Split migration into its own function To: Alistair Popple , , , , CC: , , , , , , Christoph Hellwig References: <20210304061645.29747-1-apopple@nvidia.com> <20210304061645.29747-5-apopple@nvidia.com> From: Ralph Campbell Message-ID: <9fa77684-149a-e6ed-296d-dc852aecea97@nvidia.com> Date: Mon, 8 Mar 2021 10:58:12 -0800 User-Agent: Mozilla/5.0 (X11; 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X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 08 Mar 2021 18:58:12.9807 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: dfe69c7b-7971-444a-46ae-08d8e2641fc9 X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=43083d15-7273-40c1-b7db-39efd9ccc17a;Ip=[216.228.112.34];Helo=[mail.nvidia.com] X-MS-Exchange-CrossTenant-AuthSource: CO1NAM11FT045.eop-nam11.prod.protection.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: DM5PR1201MB0074 X-Stat-Signature: r5uennbj1t54s5bmy1mpyjtwfm3nxdfu X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 9CD9EE0011E2 Received-SPF: none (nvidia.com>: No applicable sender policy available) receiver=imf05; identity=mailfrom; envelope-from=""; helo=NAM12-DM6-obe.outbound.protection.outlook.com; client-ip=40.107.243.80 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1615229894-725219 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 3/3/21 10:16 PM, Alistair Popple wrote: > Migration is currently implemented as a mode of operation for > try_to_unmap_one() generally specified by passing the TTU_MIGRATION flag > or in the case of splitting a huge anonymous page TTU_SPLIT_FREEZE. > > However it does not have much in common with the rest of the unmap > functionality of try_to_unmap_one() and thus splitting it into a > separate function reduces the complexity of try_to_unmap_one() making it > more readable. > > Several simplifications can also be made in try_to_migrate_one() based > on the following observations: > > - All users of TTU_MIGRATION also set TTU_IGNORE_MLOCK. > - No users of TTU_MIGRATION ever set TTU_IGNORE_HWPOISON. > - No users of TTU_MIGRATION ever set TTU_BATCH_FLUSH. > > TTU_SPLIT_FREEZE is a special case of migration used when splitting an > anonymous page. This is most easily dealt with by calling the correct > function from unmap_page() in mm/huge_memory.c - either > try_to_migrate() for PageAnon or try_to_unmap(). > > Signed-off-by: Alistair Popple > Reviewed-by: Christoph Hellwig Looks reasonable to me. I do worry a bit about code duplication. At some point in the future, it might be discovered that other combinations of TTU_XXX flags are needed in which case a careful check of try_to_migrate() and try_to_unmap() will be needed. Reviewed-by: Ralph Campbell