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Wed, 28 Sep 2022 02:57:32 +0000 Received: from BY5PR12MB4130.namprd12.prod.outlook.com ([fe80::51d9:c02b:e5a1:254b]) by BY5PR12MB4130.namprd12.prod.outlook.com ([fe80::51d9:c02b:e5a1:254b%5]) with mapi id 15.20.5676.017; Wed, 28 Sep 2022 02:57:32 +0000 Message-ID: <9d72f2ed-9a92-e67b-3af5-79050004a1a4@nvidia.com> Date: Tue, 27 Sep 2022 19:57:29 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.3.0 Subject: Re: [RFC 2/6] mm/migrate_pages: split unmap_and_move() to _unmap() and _move() Content-Language: en-US To: Yang Shi Cc: "Huang, Ying" , Alistair Popple , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , Zi Yan , Baolin Wang , Oscar Salvador , Matthew Wilcox References: <20220921060616.73086-1-ying.huang@intel.com> <20220921060616.73086-3-ying.huang@intel.com> <87o7v2lbn4.fsf@nvdebian.thelocal> <87fsgdllmb.fsf@nvdebian.thelocal> <87ill937qe.fsf@yhuang6-desk2.ccr.corp.intel.com> <46807002-c42c-1232-0938-5b48050171ee@nvidia.com> <87pmfgjnpj.fsf@nvdebian.thelocal> <87czbg2s3b.fsf@yhuang6-desk2.ccr.corp.intel.com> <240bbb01-1f26-71ee-233a-ad65313ac358@nvidia.com> <4a44bf59-a984-8ac4-c613-a03d74dc6a5a@nvidia.com> From: John Hubbard In-Reply-To: Content-Type: text/plain; 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b=aVT71yfoXSEqMOb7xs+j7nuZAtReNMZDNMkW3N/ab7FAPWWnFh/xdLbV2nlJCjk4qWZuQH sWwjrm10EDx4Ci4ZYBGxXnwlzO8y+6bYcQP9hEww/yAWM2+oC/ekerkZMxsU/gOGA2hP5r VPhJqxWii2eqZb2i2tVGVEExYttMgsQ= X-Stat-Signature: u88hhzqb6ds1kc5s1btzrc9q3eyfhem5 X-Rspamd-Queue-Id: 9D47A140004 X-Rspam-User: Authentication-Results: imf23.hostedemail.com; dkim=pass header.d=Nvidia.com header.s=selector2 header.b=YFVRFpKL; spf=pass (imf23.hostedemail.com: domain of jhubbard@nvidia.com designates 40.107.93.70 as permitted sender) smtp.mailfrom=jhubbard@nvidia.com; arc=pass ("microsoft.com:s=arcselector9901:i=1"); dmarc=pass (policy=reject) header.from=nvidia.com X-Rspamd-Server: rspam08 X-HE-Tag: 1664333855-710828 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 9/27/22 19:14, Yang Shi wrote: > IIRC, the writeback may not call generic_writepages. On my ext4 > filesystem, the writeback call stack looks like: > > @[ > ext4_writepages+1 > do_writepages+191 > __writeback_single_inode+65 > writeback_sb_inodes+477 > __writeback_inodes_wb+76 > wb_writeback+457 > wb_workfn+680 > process_one_work+485 > worker_thread+80 > kthread+231 > ret_from_fork+34 > ]: 2 > Sure, that's fine for ext4, in that particular case, but a) not all filesystems have .writepages hooked up. That's why do_writepages() checks for .writepages(), and falls back to .writepage(): if (mapping->a_ops->writepages) ret = mapping->a_ops->writepages(mapping, wbc); else ret = generic_writepages(mapping, wbc); , and b) there are also a lot of places and ways to invoke writebacks. There are periodic writebacks, and there are data integrity (WB_SYNC_ALL) writebacks, and other places where a page needs to be cleaned--so, a lot of call sites. Some of which will land on a .writepage() sometimes, even now. For just one example, I see migrate.c's writeout() function directly calling writepage(): rc = mapping->a_ops->writepage(&folio->page, &wbc); thanks, -- John Hubbard NVIDIA