On Tue 26-03-13 13:52:51, Zheng Liu wrote: > Sorry for the late reply. > > On Wed, Mar 20, 2013 at 10:45:23AM -0400, Theodore Ts'o wrote: > > On Wed, Mar 20, 2013 at 09:14:42AM -0500, Eric Sandeen wrote: > > > > > > As an aside, is there any reason to have "dioread_nolock" as an option > > > at this point? If it works now, would you ever *not* want it? > > > > > > (granted it doesn't work with some journaling options etc, but that > > > behavior could be automatic, w/o the need for special mount options). > > > > The primary restriction is that diread_nolock doesn't work when fs > > block size != page size. If your proposal is that we automatically > > enable diread_nolock when we can use it safely, that's definitely > > something to consider for the next merge window. > > Yes, I also think we can automatically enable dioread_nolock because it > brings us some benefits. But isn't there also some overhead due to buffered writes having to go through uninit->init conversion? Plus there's this potential deadlock in dioread_nolock code (http://www.spinics.net/lists/linux-ext4/msg36569.html) which I'm not sure how to fix yet... > BTW, I think there is an minor improvement for dio overwrite codepath > with indirect-based file. We don't need to take i_mutex in this > condition just as we have done for extent-based file. If a user mounts > a ext2/3 file system with a ext4 kernel modules, he/she could get a > lower latency. But it seems that it would break dio semantic in ext2/3. > Currently in ext2/3 if we issue a overwrite dio and then issue a read > dio. We will always read the latest data because we wait on i_mutex > lock. But after parallelizing overwite dio, this semantic might breaks. > I re-read this doc but it seems that it doesn't describe this case. Do > we need to keep this semantic? I'm not sure but also I don't think it's important to optimize that special case. 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
