Re: [RFC PATCH 0/8] xfs: shrink the struct xfs_icdinode

Dave Chinner
2016-01-12T21:07:22Z

On Tue, Jan 12, 2016 at 07:30:10AM -0800, Christoph Hellwig wrote:
> Nice!
>
> I had started on some of this a while ago but never finished it..

*nod*

> > 72 bytes. This means it takes 104 bytes off the size of the struct
> > xfs_inode, which a 12% reduction in size. This will be a massive win
> > for systems that cache lots of inodes!
>
> How many more inodes can we fit into a slab cache now? Back when I
> started I noticed it doesn't help us to actually fit more inodes into
> a 4k page due to the bloated VFS inode. But these days slub actually
> uses a high order allocations if I remember correctly so it might be
> more useful.

On a debug build (because that's the only numbers I have at hand),
the current code is 1280 bytes/inode, 25 inodes/slab, 8 pages/slab.
This patch set makes it 1152 bytes/inode, 28 inodes/slab, 8
pages/slab, so that's a 12% increase in the number of cached inodes
for a given amount of slab memory.

IIRC, a production build is around 960 bytes/inode, so that would
put it at 34 inodes/slab for the current code and 38 inodes/slab
for the current patchset. That, again, is roughly 12% increase in
inodes per slab....

> > With this change made, the xfs_icdinode is no long an "in core disk
> > inode" so I'm wondering whether I should rename it or simply make it
> > go away altogether and pull the remaining fields straight into the
> > struct xfs_inode. Any thoughts on new names and/or getting rid of it
> > woul dbe appreciated.
>
> I think it should be merged into the xfs_inode structure soner or
> later.

Ok, I'll look at doing that.

> Another thign I planned but never got to is to move fields
> into the inode fork that were specific to the attr or data fork.

That's a whole different problem ;)

Cheers,

Dave.

--
Dave Chinner
david@fromorbit.com