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DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1778158777; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=N+8on1rJhIM7gFzPDRKP1K79fhr5fu80l2DgfLVZ7Hc=; b=rq2dqH3LbsTDkNm64j4yfugrxYnuo1K5QSVNxsj0wf0x+gTd830yL//sZ1zls/YfFle5Ea rHimXqQZl2XdEdZH/pVmBJ7KEOCjfln0xEgi5Y+CUNGbqvdO6qsze8DrzkZ4nbLBf6umJN 4C9u2RSxqusKL26SGb9MF9QMwi4Tu3I= From: Lance Yang To: ziy@nvidia.com Cc: akpm@linux-foundation.org, david@kernel.org, willy@infradead.org, songliubraving@fb.com, clm@fb.com, dsterba@suse.com, viro@zeniv.linux.org.uk, brauner@kernel.org, jack@suse.cz, ljs@kernel.org, baolin.wang@linux.alibaba.com, Liam.Howlett@oracle.com, npache@redhat.com, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, lance.yang@linux.dev, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, shuah@kernel.org, linux-btrfs@vger.kernel.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org Subject: Re: [PATCH v5 06/14] mm: fs: remove filemap_nr_thps*() functions and their users Date: Thu, 7 May 2026 20:59:21 +0800 Message-Id: <20260507125921.6325-1-lance.yang@linux.dev> In-Reply-To: <20260429153538.727855-2-ziy@nvidia.com> References: <20260429153538.727855-2-ziy@nvidia.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: EBF93A000F X-Stat-Signature: ttrzjn14qhgsjkkw1md794cqn5cdkh4m X-Rspam-User: X-HE-Tag: 1778158780-15967 X-HE-Meta: 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 N/PjIEiS Ie6UH2LEJjImhL17Nx+2oCOKtqqcqKNgFf+6i5tRICrgrX/rGoa0T2omxHI3gJZdPw6a1deqqM9ayFnaiXt31wJkOepsnc7lu71d5aUA1kcpBYgyW/uPX5kg6W5sZvpWktr/VyOoebcVexo65E5MuNgF5EdMwnhveeGOSxUpwCXhRqa3GxfsL3b/+H27TjOooDP6FoOJzijgY3TE5mUlS/aWsI9FcPPaIzVMpQzi1EdVjzaYTsSwDMq3sO7xZ9reoHeZVG4KN4BDyC6U2lW+TxR+KTUGGgKtJlFriLL6lW5qhOPGL4z5RQobzlWgUMffjq7Qx/coQ3IT0KUao0fTe4W9MKtPlokCelaEu Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Apr 29, 2026 at 11:35:29AM -0400, Zi Yan wrote: >They are used by READ_ONLY_THP_FOR_FS to handle writes to FSes without >large folio support, so that read-only THPs created in these FSes are not >seen by the FSes when the underlying fd becomes writable. Now read-only PMD >THPs only appear in a FS with large folio support and the supported orders >include PMD_ORDER. > >READ_ONLY_THP_FOR_FS was using mapping->nr_thps, inode->i_writecount, and >smp_mb() to prevent writes to a read-only THP and collapsing writable >folios into a THP. In collapse_file(), mapping->nr_thps is increased, then >smp_mb(), and if inode->i_writecount > 0, collapse is stopped, while >do_dentry_open() first increases inode->i_writecount, then a full memory >fence, and if mapping->nr_thps > 0, all read-only THPs are truncated. > >Now this mechanism can be removed along with READ_ONLY_THP_FOR_FS code, >since a dirty folio check has been added after try_to_unmap() in >collapse_file() to prevent dirty folios from being collapsed as clean. > >Signed-off-by: Zi Yan >Reviewed-by: Matthew Wilcox (Oracle) >Acked-by: David Hildenbrand (Arm) >Reviewed-by: Baolin Wang >--- Nice cleanup! The old counter/barrier trick is no longer needed; collapse_file() now checks the thing we actually care about ;) LGTM. Reviewed-by: Lance Yang