Re: [PATCH 1/2] xfs: reorder xfs_inode structure elements to remove unneeded padding.

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Matthew Wilcox <willy@xxxxxxxxxxxxx> 于2024年6月18日周二 12:51写道:
>
> On Tue, Jun 18, 2024 at 12:40:23PM -0400, JunChao Sun wrote:
> > Darrick J. Wong <djwong@xxxxxxxxxx> 于2024年6月18日周二 12:23写道:
> > >
> > > On Tue, Jun 18, 2024 at 07:35:04PM +0800, Junchao Sun wrote:
> > > > By reordering the elements in the xfs_inode structure, we can
> > > > reduce the padding needed on an x86_64 system by 8 bytes.
> > >
> > >
> > > > Does this result in denser packing of xfs_inode objects in the slab
> > > > page?
> >
> > No. Before applying the patch, the size of xfs_inode is 1800 bytes
> > with my config, and after applying the patch, the size is 1792 bytes.
> > This slight reduction does not result in a denser packing of xfs_inode
> > objects within a single page.
>
>
> > The "config dependent" part of this is important though.  On my
> > laptop running Debian 6.6.15-amd64, xfs_inode is exactly 1024 bytes,
> > and slab chooses to allocate 32 of them from an order-3 slab.
> >
> > Your config gets you 18 from an order-3 slab, and you'd need to get
> > it down to 1724 (probably 1720 bytes due to alignment) to get 19
> > from an order-3 slab.  I bet you have lockdep or something on.

Yes.. Sorry for that. I will change the config to debian release and
then take a look again.

Thanks for your review and comments.


Best regards,
-- 
Junchao Sun <sunjunchao2870@xxxxxxxxx>





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