Re: [PATCH v2 00/10] btrfs: inode management and memory consumption improvements

[David Sterba <dsterba@suse.cz>]

On Fri, May 10, 2024 at 06:32:48PM +0100, fdmanana@kernel.org wrote:
> From: Filipe Manana <fdmanana@suse.com>
> 
> Some inode related improvements, to use an xarray to track open inodes per
> root instead of a red black tree, reduce lock contention and use less memory
> per btrfs inode, so now we can fit 4 inodes per 4K page instead of 3.

That's great, thank you very much.

The slack space per page is slightly less than 1/4 (25%) in SLUB as it
has more pages per slab per object. Depending on that it can go down to
12.5% (for 8 pages per slab). But still this is a noticeable
improvement.

The 4 byte hole after otime members is still there, we might find use
for it in the future.

I'm thinking about adding a _static_assert(sizeof(btrfs_inode) <= 1024)
on a release config (and x86_64). Given the amount of time and efforts
it took to shrink the size I want to make it visible when a deliberate
change to either struct inode or any embedded structure increases the
size again.