On 4/1/13 10:39 AM, Theodore Ts'o wrote: > On Mon, Apr 01, 2013 at 10:18:51AM -0500, Eric Sandeen wrote: >> I'd add: >> >> 3) Why do we have a "nodelalloc" mount option at all? >> >> but then I thought: >> >> Is it also this bad when using the ext4 driver to run an ext3 fs? > > Yes, and I there would be a similar performance problem if you are > using the ext3 file system driver, since ext3_*_writepage() also ends > up calling block_write_full_page() which will also result in the > writes happening with WRITE_SYNC. > The main reason why we keep nodelalloc at this point is bug-for-bug > compatibility with ext3 file systems --- basically, for users who are > using this as a workaround for the O_PONIES issue instead of fixing > their applications to use fsync() appropriately. Sorry for getting off the original thread here, but IMHO these are 2 different things: nondelalloc behavior makes sense for ext3, but: -o nodelalloc mount options don't make sense for ext4. > So another question is how much do we care about exact emulation of > ext3's behaviour for those distributions who wish to use ext4 file > system driver for ext2 and ext3 file systems? > > One of the reasons for keeping nodealloc mode was the argument was > that it removing it wouldn't really allow us to remove that much > complexity from ext4. IMHO we should keep the mode for ext2/3, but lose the ext4 option. It'd just be one less row in the ext4 test matrix. -Eric > But adding a nodealloc specific ext4_writepages > pages would result in adding a huge amount of complexity, and my first > reaction is that it's really not worth the code maintenance headache. > Dmitry, is there a reason why you are especially worried about the > performace of nodelalloc mode? > > - Ted > -- 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
