On Tue 09-04-13 17:38:21, Dmitry Monakhov wrote: > According to stable write assumptions (1d1d1a767206fb) > grab_cache_page_write_begin() now calls relaxed method wait_for_stable_page() > which will wait for writeback to finish only if bdi demand that. Yes. > Commit message states that ext4 may not wait > But there are a lot of write-paths where we expect that: > BUG_ON(!PageLocked(page)); > BUG_ON(PageWriteback(page)); Really? The only places I can find are in writeback path and there we have wait_on_page_writeback() (either in write_cache_pages() or in ext4_da_writepages()). > And the only reason we avoid this bugon is because of commit 47564bfb95b > which use following trick to avoid lock inversion over journal_start: > page = grab_cache_page_write_begin() > unlock_page(page); > ext4_journal_start() > lock_page(page); > wait_on_page_writeback(page); <<<< unconditional wait No, I think this is really independent. ext4 should be fine when write & writeback are running in parallel for a page. > So as far as I understand this was done just by occasion because > ext4_page_mkwrite() use wait_for_stable_page(). > > So here is my question: Do we have to wait for page's writeback to > finish for all write paths in ext4 code or we may use > wait_for_stable_page() and should cleanup all places where > we may trigger BUG_ON(PageWriteback(page)); If there's any such place, please tell me how we could trigger it... Honza -- Jan Kara <jack@xxxxxxx> SUSE Labs, CR -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
