On Wed 17-04-13 11:39:27, Dmitry Monakhov wrote: > On Mon, 15 Apr 2013 14:29:13 +0200, Jan Kara <jack@xxxxxxx> wrote: > > On Sun 14-04-13 23:01:34, Dmitry Monakhov wrote: > > > Current implementation of jbd2_journal_force_commit() is suboptimal because > > > result in empty and useless commits. But callers just want to force and wait > > > any unfinished commits. We already has jbd2_journal_force_commit_nested() > > > which does exactly what we want, except we are guaranteed that we do not hold > > > journal transaction open. > > Umm, I have a questions regarding this patch: > > Grep shows there are just two places in the code which use > > ext4_force_commit() (and thus jbd2_journal_force_commit()). These are > > ext4_write_inode() and ext4_sync_file() (in data=journal mode). The first > > callsite can use _nested() variant immediately as we even assert there's > > no handle started. The second call site can use the _nested variant as well > > because if we had the transaction started when entering ext4_sync_file() we > > would have serious problems (lock inversion, deadlocks in !data=journal > > modes) anyway. So IMO there's no need for !nested variant at all (at least > > in ext4, ocfs2 uses it as well, IMHO it can be converted as well but that's > > a different topic). Thoughts? > I'm not sure that I completely understand what you meant, but it seems > incorrect to use jbd2_journal_force_commit_nested() in > ext4_write_inode() and ext4_sync_file(). Because nested variant has > probabilistic behavior, It may skip real transaction commit if we hold > a transaction running. ext4_write_inode() and ext4_sync_file() > are the functions where we demand deterministic behavior. If we silently > miss real transaction commit because current->journal_info != NULL (due > to some bugs) this breaks data integrity assumptions and it is better to > make it loud and trigger a BUGON. I see. I was confused by the fact that 'nested' argument got used only in the assertion but now I see why that is. 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
