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Thu, 20 Jul 2023 07:51:31 -0700 (PDT) Message-ID: <251d9862-e335-243e-d65a-c5538b4df253@redhat.com> Date: Thu, 20 Jul 2023 09:51:30 -0500 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.13.0 Subject: Re: allow building a kernel without buffer_heads To: Christoph Hellwig , Jens Axboe Cc: "Darrick J. Wong" , Andrew Morton , Matthew Wilcox , Christian Brauner , linux-block@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-xfs@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, cluster-devel References: <20230720140452.63817-1-hch@lst.de> From: Bob Peterson In-Reply-To: <20230720140452.63817-1-hch@lst.de> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 94FEA40012 X-Rspam-User: X-Rspamd-Server: rspam02 X-Stat-Signature: 7btbrmw57mresh9kaxyf5emxhohbe1zu X-HE-Tag: 1689864697-393521 X-HE-Meta: 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 xqCtnhvD l+ZU0mweQhQcs/cyJ9/2o+HYvxtri0o6JaE35k1jaNBsPmsaGlFtqTIY5saltI05FOAHIZPjFfFgcZJZ/Yg1kwBhCUO0PYKpUEAVwtA9U+tx3LIPfQeqb6eT/YJqEdmslznO0+Q3UWp59RXh6QRXKvgGo/W71X7ecSU4Rl6SzNIFyFSuAzOwL2WzUQFjQwGbDWO5OFx7NUUAQJEvvsr98wNNAZjbG2ueBDzAEEXLxTktb8ExPVQkWYZF9CDuvpMO0SZiocUy+0VOgbK5ZnF23tiagUtb+x9+S8fuWJNRP/5pLnm1IrvwqV7T13OD1O4SDX4RCwjyEVf1BZYSJ6y3C9H4DgUo53n4HeyFZm2Dea9vIznlNDicH1uKWCnTzdPr6iCm5D31J2m92JGENI/F7qWW5rhb8PeAmd97/ 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: On 7/20/23 9:04 AM, Christoph Hellwig wrote: > Hi all, > > This series allows to build a kernel without buffer_heads, which I > think is useful to show where the dependencies are, and maybe also > for some very much limited environments, where people just needs > xfs and/or btrfs and some of the read-only block based file systems. > > It first switches buffered writes (but not writeback) for block devices > to use iomap unconditionally, but still using buffer_heads, and then > adds a CONFIG_BUFFER_HEAD selected by all file systems that need it > (which is most block based file systems), makes the buffer_head support > in iomap optional, and adds an alternative implementation of the block > device address_operations using iomap. This latter implementation > will also be useful to support block size > PAGE_SIZE for block device > nodes as buffer_heads won't work very well for that. > > Note that for now the md software raid drivers is also disabled as it has > some (rather questionable) buffer_head usage in the unconditionally built > bitmap code. I have a series pending to make the bitmap code conditional > and deprecated it, but it hasn't been merged yet. > > Changes since v1: > - drop the already merged prep patches > - depend on FS_IOMAP not IOMAP > - pick a better new name for block_page_mkwrite_return > Hi Christoph, Gfs2 still uses buffer_heads to manage the metadata being pushed through its journals. We've been reducing our dependency on them but eliminating them altogether is a large and daunting task. We can still work toward that goal, but it will take time. Bob Peterson