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Thu, 18 Dec 2025 16:27:51 -0800 (PST) Received: from groves.net ([2603:8080:1500:3d89:7cbc:db2c:ec63:19af]) by smtp.gmail.com with ESMTPSA id 46e09a7af769-7cc6673ccc2sm663236a34.12.2025.12.18.16.27.49 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 18 Dec 2025 16:27:50 -0800 (PST) Date: Thu, 18 Dec 2025 18:27:49 -0600 From: John Groves To: Andrew Morton Cc: Alistair Popple , David Hildenbrand , Oscar Salvador , John Groves , "Darrick J . Wong" , Dan Williams , Gregory Price , Balbir Singh , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-cxl@vger.kernel.org, linux-fsdevel@vger.kernel.org, Aravind Ramesh , Ajay Joshi Subject: Re: [PATCH] mm/memremap: fix spurious large folio warning for FS-DAX Message-ID: References: <20251217211310.98772-1-john@groves.net> <74npmrpzagba2bbye7kmwwoguafbpvnkxarprp3txy4wmu6gxp@japia7ysaisi> <20251218160332.ee5b1c9b2ac7aebabbabfa45@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20251218160332.ee5b1c9b2ac7aebabbabfa45@linux-foundation.org> X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 87BD218000D X-Stat-Signature: 89er6yj87ooen43cqgx61ycrq6cpujdr X-Rspam-User: X-HE-Tag: 1766104072-908824 X-HE-Meta: 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 dGW89LWs 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 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 25/12/18 04:03PM, Andrew Morton wrote: > On Thu, 18 Dec 2025 09:58:02 +1100 Alistair Popple wrote: > > > On 2025-12-18 at 08:13 +1100, John Groves wrote... > > > From: John Groves > > > > > > This patch addresses a warning that I discovered while working on famfs, > > > which is an fs-dax file system that virtually always does PMD faults > > > (next famfs patch series coming after the holidays). > > > > > > However, XFS also does PMD faults in fs-dax mode, and it also triggers > > > the warning. It takes some effort to get XFS to do a PMD fault, but > > > instructions to reproduce it are below. > > > > > > The VM_WARN_ON_ONCE(folio_test_large(folio)) check in > > > free_zone_device_folio() incorrectly triggers for MEMORY_DEVICE_FS_DAX > > > when PMD (2MB) mappings are used. > > > > > > FS-DAX legitimately creates large file-backed folios when handling PMD > > > faults. This is a core feature of FS-DAX that provides significant > > > performance benefits by mapping 2MB regions directly to persistent > > > memory. When these mappings are unmapped, the large folios are freed > > > through free_zone_device_folio(), which triggers the spurious warning. > > > > Yep, and I'm pretty sure devdax can also create large folios so we might need > > a similar fix there. In fact looking at old vs. new code it seems we only ever > > used to have this warning for anon folios, which I think could only ever be true > > for DEVICE_PRIVATE or DEVICE_COHERENT folios. > > > > So I suspect the proper fix is to just remove the warning entirely now that they > > also support compound sizes. > > So I'm assuming we can expect an updated version of this fix. I'll send an update Friday morning Thanks Alistair, Dan and Andrew! John