On Wed, Dec 04, 2013 at 01:50:52PM +0800, Zheng Liu wrote:
> [Cc Tao to get some comments]
>
> On Tue, Dec 03, 2013 at 09:26:08PM -0800, Darrick J. Wong wrote:
> > On Wed, Dec 04, 2013 at 01:21:50PM +0800, Zheng Liu wrote:
> > > On Tue, Dec 03, 2013 at 08:08:19PM -0800, Darrick J. Wong wrote:
> > > > On Wed, Dec 04, 2013 at 11:27:57AM +0800, Zheng Liu wrote:
> > > > > On Tue, Dec 03, 2013 at 02:30:26PM -0800, Darrick J. Wong wrote:
> > > > > [...]
> > > > > > > + * notify users that inline data will never be useful.
> > > > > > > + */
> > > > > > > + if ((fs_param.s_feature_incompat &
> > > > > > > + EXT4_FEATURE_INCOMPAT_INLINE_DATA) &&
> > > > > > > + inode_size == EXT2_GOOD_OLD_INODE_SIZE) {
> > > > > >
> > > > > > Perhaps I'm missing something here, but why is it impossible to use i_blocks
> > > > > > for inline data even if there's no space for EAs?
> > > > >
> > > > > If I understand correctly, on kernel side, we determine an inode has
> > > > > inline data according to whether we have 'system.data' xattr entry on
> > > > > inode extended attribute space. If an inode doesn't have enough space
> > > > > to store an entry with 'system.data', we just think this inode doesn't
> > > > > has inline data. So that is why I add this sanity check.
> > > >
> > > > Ok. I was curious. Small inode => no inline data seems like an unfortunate
> > > > restriction to me, but oh well, it's your feature. I don't plan to go back to
> > > > 128 byte inodes ever. :)
> > > >
> > > > Also, we could store four more bytes if we created a new e_name_index value (5?
> > > > 9?) to represent "system.data". Any thoughts about that?
> > >
> > > Sorry, I don't get your point. Do you want to create a new e_name_index?
> > > Any reason lets you want to do this?
> >
> > Yep, that's exactly what I propose to do, so we can cram four more bytes into
> > the inline data.
>
> Agree. I believe it is fine. But I am wondering if it will break the
> file system that inline data has been enabled.
There's a fair amount of work needed for fs/ext4/inline.c. My e2fsprogs thing
should handle it fine, though I think the inlinedata_max_size function
somewhere in your patchset might also be broken.
I suspect a lot depends on how widely deployed inlinedata is inside Taobao, or
anyone else who's actually running it right now.
--D
>
> - Zheng
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