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h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=yV3mq70NowsKzsNN4Ez+jnFDFJRIlhbNscdaUiVTLxZRecRmCbvgybiz9uRsrgg0n PjP3lsjSFoN3ZHe8QI2pdayWSJuwfonJJuwBr3DLAHViSi3MWsPfptWuWaWljJtEVC tmLb8vkj5Dj4ezW3MMOW7Coe5YQtHTHUai0uWSDo= Date: Tue, 7 Jan 2025 22:26:43 -0800 From: Andrew Morton To: Alistair Popple Cc: dan.j.williams@intel.com, linux-mm@kvack.org, lina@asahilina.net, zhang.lyra@gmail.com, gerald.schaefer@linux.ibm.com, vishal.l.verma@intel.com, dave.jiang@intel.com, logang@deltatee.com, bhelgaas@google.com, jack@suse.cz, jgg@ziepe.ca, catalin.marinas@arm.com, will@kernel.org, mpe@ellerman.id.au, npiggin@gmail.com, dave.hansen@linux.intel.com, ira.weiny@intel.com, willy@infradead.org, djwong@kernel.org, tytso@mit.edu, linmiaohe@huawei.com, david@redhat.com, peterx@redhat.com, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, nvdimm@lists.linux.dev, linux-cxl@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org, linux-xfs@vger.kernel.org, jhubbard@nvidia.com, hch@lst.de, david@fromorbit.com Subject: Re: [PATCH v5 00/25] fs/dax: Fix ZONE_DEVICE page reference counts Message-Id: <20250107222643.80d5509219d6b66c15b1b8af@linux-foundation.org> In-Reply-To: References: X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: ED4DD1A000A X-Stat-Signature: b4cctzr6jbap17zodea7d3eddnmg6rwf X-Rspam-User: X-Rspamd-Server: rspam09 X-HE-Tag: 1736317606-301952 X-HE-Meta: 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 h0TsVf5m Q5LyzKDZFOwBznSbVnbsdHX+Wgs7EtqzJ9WJ45ENIOJEgSHMalB5L5vfmvA2ca0JXgFkpbxRO5cbceuBe2+kBsS8EepVtSYjpmE/mLog9KaUfaZc2afMyWyDYhX6LvYcb28CJ/1iqkkAaloLGnm2Pgu9CJnHpniuELvV9i4NMGCqqkayRGIpi4+TxvdPIK3CZjl35h67tcWl8+NdCEgxLnEX/US/X+HaZCODJ4z9c7xD2EgnFmIKe0cWVLx8VTH4BPHcGSVx3aUe2j0oJaZ79djNG8U0DNgI3YI8XMN7YARWAxh9waVgaBq5qv5IzndqDl/xBUBmyHV172Ip3HMQpSihs8ajzrqHjHZWUSY6qA8/8aN6PrTO78uTeKKHAndc04BhGjmEW6jIqnBblk6IfuFClyy5MOSUCC9ue 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 Tue, 7 Jan 2025 14:42:16 +1100 Alistair Popple wrote: > Device and FS DAX pages have always maintained their own page > reference counts without following the normal rules for page reference > counting. In particular pages are considered free when the refcount > hits one rather than zero and refcounts are not added when mapping the > page. > > Tracking this requires special PTE bits (PTE_DEVMAP) and a secondary > mechanism for allowing GUP to hold references on the page (see > get_dev_pagemap). However there doesn't seem to be any reason why FS > DAX pages need their own reference counting scheme. > > By treating the refcounts on these pages the same way as normal pages > we can remove a lot of special checks. In particular pXd_trans_huge() > becomes the same as pXd_leaf(), although I haven't made that change > here. It also frees up a valuable SW define PTE bit on architectures > that have devmap PTE bits defined. > > It also almost certainly allows further clean-up of the devmap managed > functions, but I have left that as a future improvment. It also > enables support for compound ZONE_DEVICE pages which is one of my > primary motivators for doing this work. > https://lkml.kernel.org/r/wysuus23bqmjtwkfu3zutqtmkse3ki3erf45x32yezlrl24qto@xlqt7qducyld made me expect merge/build/runtime issues, however this series merges and builds OK on mm-unstable. Did something change? What's the story here? Oh well, it built so I'll ship it!