On Tue, 9 Apr 2013 16:28:05 +0200, Jan Kara <jack@xxxxxxx> wrote: > 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... move_extent.c:mext_page_mkuptodate() expect that. IMHO it is reasonable to force behavior here even if we may not do that on other places because defragmentation code should be 101% reliable and performance is not important here. > > 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
