From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bob Peterson Date: Thu, 20 Jul 2023 09:51:30 -0500 Subject: [Cluster-devel] allow building a kernel without buffer_heads In-Reply-To: <20230720140452.63817-1-hch@lst.de> References: <20230720140452.63817-1-hch@lst.de> Message-ID: <251d9862-e335-243e-d65a-c5538b4df253@redhat.com> List-Id: To: cluster-devel.redhat.com MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit 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