On Mon, Oct 18, 2021 at 11:16:08AM -0600, Jens Axboe wrote:

This looks good to me. Followup question, as it's related - I've got a
hacky patch that caches the inode size in the bdev:

https://git.kernel.dk/cgit/linux-block/commit/?h=perf-wip&id=c754951eb7193258c35a574bd1ccccb7c4946ee4

so we don't have to dip into the inode itself for the fast path. While
it's obviously not something being proposed for inclusion right now, is
there a world in which we can make something like that work?

There's just two places that update i_size for block devices:
set_capacity and bdev_set_nr_sectors.  So you just need to update
bd_nr_sectors there and you're done.