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smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=JGMdQPeY; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A5611606A33E; Fri, 6 Nov 2026 22:42:40 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=JGMdQPeY Received: by smtp.kernel.org (Postfix) with ESMTPSA id DFFDB1F008A1; Fri, 6 Nov 2026 22:42:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794004960; bh=JlbEJ/mAQ5AEryfKs406khz/jZEGvS7oBKVbDoRy+Xo=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=JGMdQPeYWvZkx75geWZtgyTHasxq12eL2mvw130fUowkgQt5u/0QMWgjSwtPkrv9x nAmjmlLC7P72HaNBsSW594Z2aGntB2xZRIbb1q2R8ZtMH3EYlK1ql87XNKKuF6C8g9 YgeHFDQ0cWMuaQUVjBvcVGKQAJpu6mwtlDJ0sGswiWtLGmASIR6/6q4X0dEpOAE2eF iNsdg9qv5vVMyNNORv0rIQQxNkFL+m6shCr1VUsNJuYFfxAv45qwMOjzvRCmv+QD+r SbMFCEmReiNw5AyNldI87KX38Qhwj6dZrU+wBDI8Sqtq/2STIRj0mAqTnzOzfGK3Zx OkxQrVY8oZSWw== Message-ID: <6b8d6030-efe7-47d2-8aa2-3f8fd77ce95c@kernel.org> Date: Fri, 6 Nov 2026 22:57:19 +0100 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 2/5] mm: limit pagecache folio refcount when splicing into pipes To: Lance Yang Cc: akpm@linux-foundation.org, ljs@kernel.org, liam@infradead.org, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, willy@infradead.org, jack@suse.cz, ziy@nvidia.com, baolin.wang@linux.alibaba.com, nico.pache@linux.dev, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, usama.arif@linux.dev, kas@kernel.org, matthew.brost@intel.com, joshua.hahnjy@gmail.com, byungchul@sk.com, gourry@gourry.net, ying.huang@linux.alibaba.com, apopple@nvidia.com, peterx@redhat.com, hannes@cmpxchg.org, songliubraving@fb.com, riel@surriel.com, hughd@google.com, will@kernel.org, aneesh.kumar@kernel.org, npiggin@gmail.com, peterz@infradead.org, jgg@ziepe.ca, kevin.tian@intel.com, joro@8bytes.org, robin.murphy@arm.com, steven.sistare@oracle.com, jhubbard@nvidia.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-arch@vger.kernel.org, iommu@lists.linux.dev, stable@vger.kernel.org References: <20261105-refcount_overflow_stable-v1-2-70b9c655da3e@kernel.org> <20261106100320.77084-1-lance.yang@linux.dev> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 11/6/26 11:03, Lance Yang wrote: > > On Thu, Nov 05, 2026 at 02:10:11PM +0100, David Hildenbrand (Arm) wrote: >> Similar to mapping pagecache folios into page tables, let's reject splicing >> folios into a pipe if the refcount is at it's limit, similar to how we >> handle it during GUP. >> >> This will prevent more cases of possible folio refcount overflows with >> large pagecache folios. >> >> Let's keep it simple and check in the two callers of >> splice_folio_into_pipe(). >> >> Also check in try_get_page() to cover pipe-buffer duplication by tee() >> and partial pipe-to-pipe splicing. > > What about fuse_ref_folio()? Buffered FUSE_WRITE requests can carry > pagecache folios into a pipe through /dev/fuse without going through > splice_folio_into_pipe() or try_get_page() ... Of course it has its own handling ... :) Thanks! I was hoping the number of folio references would be bounded ... I guess one reference per pipe buffer is not the end of the world, but, let's just add it, and fallback to copying. -- Cheers, David