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Received: from willy by casper.infradead.org with local (Exim 4.98 #2 (Red Hat Linux)) id 1tqGAc-0000000B60f-1WkZ; Thu, 06 Mar 2025 18:42:10 +0000 Date: Thu, 6 Mar 2025 18:42:10 +0000 From: Matthew Wilcox To: Gregory Price Cc: Bharata B Rao , linux-kernel@vger.kernel.org, linux-mm@kvack.org, AneeshKumar.KizhakeVeetil@arm.com, Hasan.Maruf@amd.com, Jonathan.Cameron@huawei.com, Michael.Day@amd.com, akpm@linux-foundation.org, dave.hansen@intel.com, david@redhat.com, feng.tang@intel.com, hannes@cmpxchg.org, honggyu.kim@sk.com, hughd@google.com, jhubbard@nvidia.com, k.shutemov@gmail.com, kbusch@meta.com, kmanaouil.dev@gmail.com, leesuyeon0506@gmail.com, leillc@google.com, liam.howlett@oracle.com, mgorman@techsingularity.net, mingo@redhat.com, nadav.amit@gmail.com, nphamcs@gmail.com, peterz@infradead.org, raghavendra.kt@amd.com, riel@surriel.com, rientjes@google.com, rppt@kernel.org, shivankg@amd.com, shy828301@gmail.com, sj@kernel.org, vbabka@suse.cz, weixugc@google.com, ying.huang@linux.alibaba.com, ziy@nvidia.com, dave@stgolabs.net, yuanchu@google.com, hyeonggon.yoo@sk.com Subject: Re: [RFC PATCH 1/4] mm: migrate: Allow misplaced migration without VMA too Message-ID: References: <20250306054532.221138-1-bharata@amd.com> <20250306054532.221138-2-bharata@amd.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam02 X-Stat-Signature: gcdnyt3egdko9zo949jh4f3oeeqp5ke6 X-Rspamd-Queue-Id: 1256E4000D X-Rspam-User: X-HE-Tag: 1741286538-208855 X-HE-Meta: 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 XahPdBRb BEGvcLJ3/ZHjhtW04yCOXNQLyNPfwFMCHgvWLxzi3IO/PERrrHG40S9TQI8Pw3SmqDAbg0+g4ziMmzBlykVk2QVyueoQ1SwssRHhS5+iwS5xTMMBPTvy1vigzxu0wXzFVu3h6WpmYPqy00JXaERXX1c3Wy/Nxdl2S7ufY8YBB/JZ4JM2t9n2bpB2x57kNvI5iqheMkccFIZ1IRmLBCvG/YZ1gCg93FxRNFgNKrdhCoTiamuRAhDHzrXqBig2lqHJZSnju7vU427FDiXvDqgMdELK/HN2hV/5XpOAqw+2Ol5S96V33FAdXkDUaILjPso/739jp09CTU295mFLxZtjH1LIr1Y0tc3JIQVdL8uaDy2OJ8dF7vsl1nbFOGyukpXqV9r2n 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: List-Subscribe: List-Unsubscribe: On Thu, Mar 06, 2025 at 01:19:41PM -0500, Gregory Price wrote: > On Thu, Mar 06, 2025 at 05:45:34PM +0000, Matthew Wilcox wrote: > > On Thu, Mar 06, 2025 at 12:24:16PM -0500, Gregory Price wrote: > > > we may also need this: > > > https://lore.kernel.org/linux-mm/20250107000346.1338481-4-gourry@gourry.net/ > > > > > > May be worth just pulling these ahead to avoid conflict. > > > > Or not putting them in at all because this whole thing is a magnificent > > waste of time? > > Divorced from the tiering mechanisms, is making misplaced migration able > to migrate unmapped pages not generally useful? The only thing I can think of is if you have a process or set of processes on node A calling read() and the file is cached on node B. But in order to decide if the page is on the wrong node, you'd need to track a lot of information about which nodes the page is being accessed from. Which is probably why we've never bothered to do it. This is not a large patch for you to carry as part of your patchset. There's nothing intrinsically wrong with it; it just has no users in mainline and no real prospect of any being added soon.