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Received: from willy by casper.infradead.org with local (Exim 4.98.2 #2 (Red Hat Linux)) id 1wDVbY-00000002Lys-0Xsb; Thu, 16 Apr 2026 22:54:36 +0000 Date: Thu, 16 Apr 2026 23:54:35 +0100 From: Matthew Wilcox To: Miklos Szeredi Cc: Nikolay Amiantov , fuse-devel@lists.sourceforge.net, linux-fsdevel , Amir Goldstein , fuse-devel@lists.linux.dev, linux-mm Subject: Re: [fuse-devel] Debugging a stale kernel cache during file growth Message-ID: References: <898a4e10-6193-4671-b3b1-7c7bc562a671@fmap.me> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Queue-Id: 5970380004 X-Stat-Signature: bw8umqiqhjoijbhoisyd4eia7ostd1zm X-Rspam-User: X-Rspamd-Server: rspam09 X-HE-Tag: 1776380080-162345 X-HE-Meta: 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 7G7xFH2I LFrRvOa2/k4qWiJmIgI9c4pv3UeU0s9IZIallAz7uPFYbpIkjlNg3cCF65X9DbUy69grPk2IF8+IA8IkCNTD2oT0LA8mytBXd+FRlX3L65pgMNmV3+I9scNhM8DIik+ma+JI4KvEhJBYWXEQ3axdNfNZJIGSIQnNIz6m2eIgTb44HqHhWlnxqR/rNHf8ZQ7/XGFscagPLsEg1A9/8kAwhxeuwXCY7nAQS0IdBcNvHhZhynDfU7Nsv3gyyePiUNNuvyyXDoPH+l8+yi2k= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, Apr 16, 2026 at 02:12:37PM +0200, Miklos Szeredi wrote: > On Thu, 16 Apr 2026 at 09:24, Amir Goldstein wrote: > > > > I've recently encountered a weird issue with JuiceFS [1], a network FS > > > which uses FUSE. tl;dr: when a file was being slowly appended, a reader > > > of the same file on another host would periodically read a block of zero > > > bytes instead of the actual data. > > Thanks for the report. > > I wonder if we could clear PG_uptodate on the page which had its zero > bytes exposed by the i_size increase? > > Willy? I think every filesystem which clear PG_uptodate is doing it wrong. I know we have ~30 places which do it, and I haven't audited them all, but clearing the uptodate bit can lead to the VM throwing an absolute fit if any of the pages in that folio are mapped. I don't think it'll make much difference whether it's cleared or invalidated from the page cache. Either way we're re-reading all the data in it, which would dominate the time saved by not doing a trip through the page allocator.