On Sep 28, 2020, at 1:41 PM, Mauricio Faria de Oliveira <mfo@xxxxxxxxxxxxx> wrote: > > These are two fixes for data journalling required by > the next patch, discovered while testing it. > > First, the optimization to return early if all buffers > are mapped is not appropriate for the next patch: > > The inode _must_ be added to the transaction's list in > data=journal mode (so to write-protect pages on commit) > thus we cannot return early there. > > Second, once that optimization to reduce transactions > was disabled for data=journal mode, more transactions > happened, and occasionally hit this warning message: > 'JBD2: Spotted dirty metadata buffer'. > > Reason is, block_page_mkwrite() will set_buffer_dirty() > before do_journal_get_write_access() that is there to > prevent it. This issue was masked by the optimization. > > So, on data=journal use __block_write_begin() instead. > This also requires page locking and len recalculation. > (see block_page_mkwrite() for implementation details.) > > Finally, as Jan noted there is little sharing between > data=journal and other modes in ext4_page_mkwrite(). > > However, a prototype of ext4_journalled_page_mkwrite() > showed there still would be lots of duplicated lines > (tens of) that didn't seem worth it. > > Thus this patch ends up with an ugly goto to skip all > non-data journalling code (to avoid long indentations, > but that can be changed..) in the beginning, and just > a conditional in the transaction section. > > Well, we skip a common part to data journalling which > is the page truncated check, but we do it again after > ext4_journal_start() when we re-acquire the page lock > (so not to acquire the page lock twice needlessly for > data journalling.) > > Signed-off-by: Mauricio Faria de Oliveira <mfo@xxxxxxxxxxxxx> > Suggested-by: Jan Kara <jack@xxxxxxx> Thanks for the clear commit message. It definitely would not be clear why the patch was structured in this way without it. Reviewed-by: Andreas Dilger <adilger@xxxxxxxxx> Cheers, Andreas
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