On Thu 30-07-09 13:39:12, Eric Sandeen wrote: > Jan Kara wrote: > >> On Tue, Jul 28, 2009 at 05:28:05PM -0700, Curt Wohlgemuth wrote: > > ... > > >> 2) We can modify the ext4_ext_convert_to_initialized() to be more > >> aggressive about initializing data blocks if we know we are doing DIO, > >> since zero'ing an aligned 16 to 32 blocks and then waiting for the > >> journal commit once is cheaper than converting the extent one block at > >> a time and waiting for the journal commit after each block write. > > Definitely. I'm not following the discussion too much in detail but > > what seems to me is the following could work: > > The direct IO path would first send all the data to disk to the > > desired location (get_block wouldn't do any conversion, just map blocks). > > When this is done, we convert all the touched extents to initialized ones > > from ext4_direct_IO, update i_size if needed, and wait for transaction > > commit. > > > > Honza > > This is all about right, but it's tricky, because right now, get_block > is called in the direct IO path from get_more_blocks(), and it's called > with create == 0 unless OWN_LOCKING is specified. If we do get_block w/ > create == 0 and find prealloc'd blocks, then we're given back unmapped > buffer heads. This looks like a hole, and so DIO falls back to buffered. > > Right now the only way to get create == 1 sent to get_blocks via > directio is to do OWN_LOCKING, which implies... we have to do our own > locking, and it'll take some time to get it right I think. But the get_block function called by get_more_blocks() is specified in ext4_direct_IO. So we can provide it with a special direct_IO version of get_block function which happily maps also uninitialized extents... It's a slight hack, but maintainable IMHO. 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
