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Wed, 29 Oct 2025 06:21:55 -0400 (EDT) Date: Wed, 29 Oct 2025 10:21:53 +0000 From: Kiryl Shutsemau To: Hugh Dickins Cc: Andrew Morton , David Hildenbrand , Matthew Wilcox , Alexander Viro , Christian Brauner , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Rik van Riel , Harry Yoo , Johannes Weiner , Shakeel Butt , Baolin Wang , "Darrick J. Wong" , Dave Chinner , linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCHv2 2/2] mm/truncate: Unmap large folio on split failure Message-ID: References: <20251023093251.54146-1-kirill@shutemov.name> <20251023093251.54146-3-kirill@shutemov.name> <9c7ae4c5-cc63-f11f-c5b0-5d539df153e1@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Queue-Id: E69ACA0003 X-Rspamd-Server: rspam11 X-Rspam-User: X-Stat-Signature: qb5yshhct1omi8ftskfkjq4ye1etjz6r X-HE-Tag: 1761733317-421051 X-HE-Meta: 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 RqfIjhph Udx1jnveM0C+ZWMkuBg3CBp6jr6L6GuLcgpj64WIGm2vFPAhXq1dDWaWDi11EMJR6AEmutrXdUxIJQpJrqd/M/G8utn1mljPipw/8R6OojBgJ5D/OqMPxIf0LEeshEIHl4Pd9I9LJ2ZeebhULbYCWsFbK0jPexRuuuZKxtlvO40q1dzmZGtKMUC2VI2f5/xrev+xCj50jurLIfNJ59nrLS6BC5QvMi1eWsM2bNsNxShnWY3ttsF09bzOXa7etSXATQXJ9wLoiIcKKC6tZB+QqllLnJreqGA2I5Uyd7i9X+BfOTjX4Aom9DkkPHySFTycec2PbW9GjIrztYTN2oJJabiQ8Z6DjQDEJvt2mslc1sjDP8+zAz45SAENeLe4P8nemi7XCaiQk/koj+op6LEbgkcic71v5bmc56s9aTKw9jz4+VLUC7UpJY1frlWB+wyHQamPl 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 Wed, Oct 29, 2025 at 02:12:48AM -0700, Hugh Dickins wrote: > On Mon, 27 Oct 2025, Kiryl Shutsemau wrote: > > On Mon, Oct 27, 2025 at 03:10:29AM -0700, Hugh Dickins wrote: > ... > > > > > Aside from shmem/tmpfs, it does seem to me that this patch is > > > doing more work than it needs to (but how many lines of source > > > do we want to add to avoid doing work in the failed split case?): > > > > > > The intent is to enable SIGBUS beyond EOF: but the changes are > > > being applied unnecessarily to hole-punch in addition to truncation. > > > > I am not sure much it should apply to hole-punch. Filesystem folks talk > > about writing to a folio beyond round_up(i_size, PAGE_SIZE) being > > problematic for correctness. I have no clue if the same applies to > > writing to hole-punched parts of the folio. > > > > Dave, any comments? > > > > Hm. But if it is problematic it has be caught on fault. We don't do > > this. It will be silently mapped. > > There are strict rules about what happens beyond i_size, hence this > patch. But hole-punch has no persistent "i_size" to define it, and > silently remapping in a fresh zeroed page is the correct behaviour. I missed that we seems to be issuing vm_ops->page_mkwrite() on remaping the page, so it is not completely silent for filesystem and can do its thing to re-allocate metadata (or whatever) after hole-punch. So, I see unmap on punch-hole being justified. -- Kiryl Shutsemau / Kirill A. Shutemov