On Wed 23-05-07 08:37:43, Theodore Tso wrote: > On Tue, May 22, 2007 at 06:11:27PM +0200, Jan Kara wrote: > > > > while fixing some problems with preallocation in UDF, I had a look how > > ext2 solves similar problems. I found out that ext2_discard_prealloc() is > > called on every iput() from ext2_put_inode(). Is it really appropriate? I > > don't see a reason for doing so... > > I agree, it's probably not appropriate. It's been that way for a long > time, though (since 2.4.20). It's not as horrible as it seems since > unlike traditional Unix systems, we don't call iput() as often, since > for example operations like close() end up calling dput(), which > decrements the ref. count on dentry, not the inode. But it would > probably be better to check to see if i_count is 1 before deciding to > discard the preallocation. OK, but then you could move the code to drop_inode() which is called at exactly that moment... I've been thinking more about it when fixing UDF. Discarding prealloc at drop_inode() has the disadvantage that symlinks/directories will keep their preallocated blocks until inodes are evicted from memory. Which is probably why ext2 discards prealloc on iput(). > > Also I found slightly misleading the comment at ext2_release_file(). > > As far as I understand the code it isn't when /all/ files are closed but > > rather when all fd's for given filp are closed. I.e. if you open the same > > file two times, ->release will get called once for each open. Am I right? > > Yep! > > > If so, then also calling ext2_discard_prealloc() from ext2_release_file() > > is suboptimal, isn't it? > > Yes, although it's a bit better because only discaord the > preallocation if the file descriptor was opened for writing. The file > could be opened for writing by multiple file descriptors, true, but in > that case it's likely that the write pattern will be a random access one > anyway, so the preallocated region is less useful. OK, but still we could use e.g. i_writecount to check that we drop the last descriptor for writing... > P.S. Note that ext3 and ext4 use a different preallocation scheme; Yes, I know that. That's why I looked at ext2 when searching for inspiration how to fix UDF :) > still patches to fix the comments might not be a bad idea, since it > might save confusion by others later on. Ok, will write one. Honza -- Jan Kara <jack@xxxxxxx> SuSE CR Labs - 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
