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Wed, 17 Aug 2022 23:05:49 +0000 Received: from BY5PR12MB4130.namprd12.prod.outlook.com ([fe80::508d:221c:9c9e:e1a5]) by BY5PR12MB4130.namprd12.prod.outlook.com ([fe80::508d:221c:9c9e:e1a5%9]) with mapi id 15.20.5525.011; Wed, 17 Aug 2022 23:05:49 +0000 Message-ID: <20370ebb-8e63-2065-307a-81fa874eced2@nvidia.com> Date: Wed, 17 Aug 2022 16:05:47 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.12.0 Subject: Re: [PATCH v4 2/2] mm/gup.c: Refactor check_and_migrate_movable_pages() Content-Language: en-US To: Jason Gunthorpe Cc: Alistair Popple , linux-mm@kvack.org, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, "Sierra Guiza, Alejandro (Alex)" , Chaitanya Kulkarni , Dan Williams , Felix Kuehling , Logan Gunthorpe , Miaohe Lin , Muchun Song , Ralph Campbell , David Hildenbrand , Matthew Wilcox References: <487960bf67c7273ff5606c76f73bb51271bc7b90.1660269441.git-series.apopple@nvidia.com> <6b61e9bf7c65f78524db32ba3e65a7eb6b8a76a0.1660269441.git-series.apopple@nvidia.com> <87edxgvixy.fsf@nvdebian.thelocal> <87wnb7tycb.fsf@nvdebian.thelocal> From: John Hubbard In-Reply-To: Content-Type: text/plain; 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b=amhoz30flBQwZ24J81Vz2TQm7uMMdq+pozzM9wZdbHBzQnfc4DV2xO7jvN5BN20rPg0vNi Y2tkIGkMxYkyz49s5KoQbN3y4g3xVcLjVecdFmSPbXP5At7c3yc/Ck9aEQ940CaWULDhPK ZIzaJaMFtCLXOZDX57AgCVrFBLfyc5M= X-Stat-Signature: gar9rg41o6tnh3oagg8mp1nb7izp7iw6 X-Rspamd-Queue-Id: 290DA1401C5 Authentication-Results: imf09.hostedemail.com; dkim=pass header.d=Nvidia.com header.s=selector2 header.b=aOoJcaCh; spf=pass (imf09.hostedemail.com: domain of jhubbard@nvidia.com designates 40.107.93.51 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-Rspam-User: X-Rspamd-Server: rspam04 X-HE-Tag: 1660777551-705464 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 8/17/22 15:50, Jason Gunthorpe wrote: > > But why return 0 from the helper function in the first place? > The caller is looking for three distinct return code cases: 0, -EAGAIN, or some other -errno. Unless you restructure more, you need all three of those cases. The 0 case leads to the caller, __gup_longterm_locked, returning nr_pages. Here is the comment block that I recommended earlier in this thread, that documents those cases: https://lore.kernel.org/r/dc8fd102-ba30-d980-bdbb-11f39326103d@nvidia.com thanks, -- John Hubbard NVIDIA