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Date: Wed, 16 Nov 2022 14:50:16 +0100 From: Christoph Hellwig <hch@....de> To: Theodore Ts'o <tytso@....edu>, Jan Kara <jack@...e.cz>, "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>, Mingming Cao <cmm@...ibm.com> Cc: linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org, ocfs2-devel@....oracle.com, linux-mm@...ck.org Subject: generic_writepages & jbd2 and ext4 Hi all, I've recently started looking into killing off the ->writepage method, and as an initial subproject kill of external uses of generic_writepages. One of the two remaining callers s in jbd2 and I'm a bit confused about it. jbd2_journal_submit_inode_data_buffers has two comments that explicitly ask for ->writepages as that doesn't allocate data: /* * write the filemap data using writepage() address_space_operations. * We don't do block allocation here even for delalloc. We don't * use writepages() because with delayed allocation we may be doing * block allocation in writepages(). */ /* * submit the inode data buffers. We use writepage * instead of writepages. Because writepages can do * block allocation with delalloc. We need to write * only allocated blocks here. */ and these look really stange to me. ->writepage and ->writepages per their document VM/VFS semantics don't different on what they allocate, so this seems to reverse engineer ext4 internal behavior in some way. Either way looping over ->writepage just for that is rather inefficient. If jbd2 really wants a way to skip delalloc conversion can we come up with a flag in struct writeback_control for that? Is there anyone familiar enough with this code who would be willing to give it a try?
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