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Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Jan Kara , Rik van Riel , Harry Yoo , Lance Yang , Jann Horn , Alexander Viro , Christian Brauner , "Darrick J. Wong" , Carlos Maiolino , Usama Arif , Pedro Falcato , linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-xfs@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@meta.com Subject: Re: [RFC PATCH 0/5] mm: sub-folio dirty tracking for PTE-mapped mmap writes Message-ID: References: <20260903182943.662461-1-kirill@shutemov.name> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspam-User: X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 9B120C000F X-Stat-Signature: bqw8krr9uhgffr6ef6uenp1kha1w3hs5 X-HE-Tag: 1789576074-153725 X-HE-Meta: U2FsdGVkX1/Xw0G1/O7jI2MpOdcfNJjR265KsKLAsw/6YHXMztjArKeDx3cyh24li37Q+2WtunKyDrm3kE0+uAbZzmWMH7ZjTYJc7z2fmBIAij2krBGGWQmUbeOpB2P6E/u50RdBysgpqChqJzhYH0Kduz1v7RFepTqwEY+HVyT6K1no7+DaekTzKhx/+bATG+/HM+Qm+m5OtesVf9Uc+9l0zsrKQ8sd+XEDSjIA1O5Qu0XTfFiTszy76uFt6dkJRt0FRzBN9VyVVQV2DtEx2650377Anub1+gediFZmjfT39wZpVtfUMCY1ETM16IJrdJGMKtGSPd4p+rRpqhjyADUEQPXtsSjzU4noeJd7UfRgmb25idHrMoU+z0MPo2iac6WD1Tzk6gBXj04n/KZG5E0ClouKeO2Zu3wOqMI+4bZGd2bTDkVIZQaQVc/IUpRPpFCY1lRFC0SFGgWGZWf89XkuLEPK2EAkJXPg+4duXpPiZOtX+lz25MeYEz6dIGxGxzTIbMpGkuAYjAo40B9zSBPL06yTepgIY9mLg31yBB+txyRc3eIrwBmnpzjNLR2x1XxtrkqRbhKpajN3wymlmWkSiAGA2/L6WoKUpEqkbJbtjRDvFLn5TJ0+XNnZtwYlyh8E8FAVgudKB2wOyLQyGtMESDuKj3rd7A8OIxccr7mRLPcMJFvsVoXJbKZWTMWpLqMVlXRji/XKJhvEQC3oOdQ5ZZJTSvuVz5PW0dOiCtkeASVnfo2TSJUnYohvtOuK7tLoERlF7UiB6AR/GC4f9zJkTqGEfZNRb0Q0zmfktf+wXYVCUSKoClfuOA/8FtQ9pTjghMD0DYaLC6A0FaD0SqfDAvh45+YyAG0X3T45XieG/v4Ss52RJeSlCVoQo0E/URdPEndFglat43aw6UR2VMjP1JMAfkI/wTQhLgxO1vytRIdFWbPl7xGlHSJCzQjf7WIxg1ls/KKJYSz+Veu W8WLXSAj PVRjvUq97Q1C35XgUB3RbB6MzwFHOHkz2abPupSg/EBuRxPt3a0mJk+cvjuKv6f6pnKDe7Hb/sSWqjMJO9SHW5nWIqB1yu4Okl8dnp2xa761i4qY6GnJC4bZOYzLy2wj1YOaSUZGTu/9vL0GIZywEtUORslupLhJtG7gMpYDbAJhkSfnNAcM1U0f3KHh0p7TxkKPlfO+B6GvEabgMrJPNFgSUbC/dqOviKGhRaJwtplEyd6lQoSh19nYSwwsh7FHsqqnf11jrMTDPnFMTgoO+PmONr825RxENRjKPCUgLB5W9kM+bOffQQfM0p26bJKuNF+5Y/iEIx6fb5dUh4F2h910gZRWTpylN3hEX Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Sep 07, 2026 at 11:15:15AM +0100, Kiryl Shutsemau wrote: > Boris pointed me to Matthew's proposal to remove ->dirty_folio: > > https://lore.kernel.org/all/aoyWln-Gt-yvZQkE@casper.infradead.org Thanks, Boris ;-) > I agree that the current ->dirty_folio() makes little sense and that > dirtying the folio can be bundled into ->page_mkwrite(), as they are > matched 1-to-1. > > My proposal makes the distinction between making the folio writable and > making it dirty meaningful. ->page_mkwrite() allocates whatever is needed > on the filesystem side to track dirty state and drive writeback for the > *folio*, while ->dirty_folio_range() marks part of the folio dirty. Why do you think that's a meaningful distinction? We create a writable PTE because we've taken a page fault for write. There's probably a few naoseconds where the PTE is writable+clean before it becomes writable+dirty, but even then sometimes we do both pte_mkwrite() and pte_mkdirty() as an optimisation in the write fault path. > We can still drop ->dirty_folio(). A filesystem can provide > ->dirty_folio_range() if it wants fine-grained (sub-folio) dirty > tracking. > > A separate question is whether we want to avoid installing a writable PMD > entry for filesystems that want fine-grained dirty tracking. I have a > patch for this, but it deserves a separate discussion once we agree that we > want this for PTE-mapped folios first. > > Any feedback? It's very odd to be optimising for shared-writable-mmap. This is a horrid model for I/O. https://cs.brown.edu/people/acrotty/pubs/p13-crotty.pdf