Re: [PATCHSET v2 0/5] xfs: make attr forks permanent

["Darrick J. Wong" <djwong@kernel.org>]

On Sun, Jul 10, 2022 at 10:25:43PM -0700, Christoph Hellwig wrote:
> On Sat, Jul 09, 2022 at 03:48:36PM -0700, Darrick J. Wong wrote:
> > Although the race condition itself can be fixed through clever use of a
> > memory barrier, further consideration of the use cases of extended
> > attributes shows that most files always have at least one attribute, so
> > we might as well make them permanent.
> 
> I kinda hat increase the size of the inode even more, but there is no
> arguing about keeping nasty rarely used code simple vs micro-optimizing
> it.  Do you have numbers on hand on how many inodes we can cache in
> an order 0 or 1 cache before and after this?

Hm.  On my laptop running 5.18, xfs_inode before the change was 928 bytes,
and here's what it looks like:

			928 bytes
Order	Pagebytes	Slack	Objs	Slack/Objs
0	4096		384	4	96
1	8192		768	8	96
2	16384		608	17	36
3	32768		288	35	9
4	65536		576	70	9

So I guess that's why it picks order-3 slabs.

On a freshly built djwong-dev kernel, it's now 976 bytes:

			976 bytes
Order	Pagebytes	Slack	Objs	Slack/Objs
0	4096		192	4	48
1	8192		384	8	48
2	16384		768	16	48
3	32768		560	33	17
4	65536		144	67	2

Here it seems to pick order-2 slabs, which admittedly isn't great.

--D