On Wed 19-08-20 10:44:21, Jan Kara wrote: > I was thinking about this and we may need to do this somewhat differently. > I've realized that there's the slight trouble that we now use page dirty > bit for two purposes in data=journal mode - to track pages that need write > protection during commit and also to track pages which have buffers that > need checkpointing. And this mixing is making things complex. So I was > thinking that we could simply leave PageDirty bit for checkpointing > purposes and always make sure buffers are appropriately attached to a > transaction as dirty in ext4_page_mkwrite(). This will make mmap writes in > data=journal mode somewhat less efficient (all the pages written through > mmap while transaction T was running will be written to the journal during > transaction T commit while currently, we write only pages that also went > through __ext4_journalled_writepage() while T was running which usually > happens less frequently). But the code should be simpler and we don't care > about mmap write performance for data=journal mode much. Furthermore I > don't think that the tricks with PageChecked logic we play in data=journal > mode are really needed as well which should bring further simplifications. > I'll try to code this cleanup. I was looking more into this but it isn't as simple as I thought because get_user_pages() users can still modify data and call set_page_dirty() when the page is no longer writeably mapped. And by the time set_page_dirty() is called page buffers are not necessarily part of any transaction so we need to do effectively what's in ext4_journalled_writepage(). To handle this corner case I didn't find anything considerably simpler than the current code. So let's stay with what we have in ext4_journalled_submit_inode_data_buffers(), we just have to also redirty the page if we find any dirty buffers. Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
