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Tue, 07 Jan 2025 08:15:53 -0800 (PST) MIME-Version: 1.0 References: <0ed5241e-10af-43ee-baaf-87a5b4dc9694@redhat.com> <446704ab-434e-45ac-a062-45fef78815e4@redhat.com> In-Reply-To: From: Miklos Szeredi Date: Tue, 7 Jan 2025 17:15:42 +0100 X-Gm-Features: AbW1kvbpEUXzpI4gujIL0BzsqsO803aPdUPT5KniHw52BwvyoC2ZwLH6S3opfkI Message-ID: Subject: Re: [PATCH v6 4/5] mm/migrate: skip migrating folios under writeback with AS_WRITEBACK_INDETERMINATE mappings To: Shakeel Butt Cc: David Hildenbrand , Joanne Koong , Bernd Schubert , Zi Yan , linux-fsdevel@vger.kernel.org, jefflexu@linux.alibaba.com, josef@toxicpanda.com, linux-mm@kvack.org, kernel-team@meta.com, Matthew Wilcox , Oscar Salvador , Michal Hocko Content-Type: text/plain; charset="UTF-8" X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 0BC6980029 X-Stat-Signature: bjfjdqjuhtrhgswuq14qsyjxz17a7ecj X-Rspam-User: X-HE-Tag: 1736266554-465800 X-HE-Meta: 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 ERGWeqSh rbWxMP2lj51A6IVjTKLavkKeKA6GcPcDlwoq6ge/53gwkyuP6kVAaUdqhIECB3k6saq6/bFvNW6aiJuvLoTuDDKVxqmZoQYEKB8h3HCVbxiHdlhXsSGL2X4b6NBQUb5Gbg3e6iBQEjF+SE7wbA85qLclxiTWxg7aTjQN8BLFx+RRXaiiKDy/XPaZXkTdAdoKw2OyTgF7Si5Mu6VRUjb0PGjfT+Ai0Jt1e5RxhpyyXVtRAhViemWMkIyV08D6LOMx3CLzlg7MMHlr6nxg= X-Bogosity: Ham, tests=bogofilter, spamicity=0.009936, 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 Mon, 6 Jan 2025 at 19:17, Shakeel Butt wrote: > > On Mon, Jan 06, 2025 at 11:19:42AM +0100, Miklos Szeredi wrote: > > On Fri, 3 Jan 2025 at 21:31, David Hildenbrand wrote: > > > In any case, having movable pages be turned unmovable due to persistent > > > writaback is something that must be fixed, not worked around. Likely a > > > good topic for LSF/MM. > > > > Yes, this seems a good cross fs-mm topic. > > > > So the issue discussed here is that movable pages used for fuse > > page-cache cause a problems when memory needs to be compacted. The > > problem is either that > > > > - the page is skipped, leaving the physical memory block unmovable > > > > - the compaction is blocked for an unbounded time > > > > While the new AS_WRITEBACK_INDETERMINATE could potentially make things > > worse, the same thing happens on readahead, since the new page can be > > locked for an indeterminate amount of time, which can also block > > compaction, right? > > Yes locked pages are unmovable. How much of these locked pages/folios > can be caused by untrusted fuse server? A stuck server would quickly reach the background threshold at which point everything stops. So my guess is that accidentally this won't do much harm. Doing it deliberately (tuning max_background, starting multiple servers) the number of pages that are permanently locked could be basically unlimited. Thanks, Miklos