It looks from profiles like ext4_getattr() is fairly expensive,
because it unnecessarily accesses the extended inode information and
causes extra cache misses.

On an empty kernel allmodconfig build (which is a lot of "stat()"
calls by Make, and a lot of silly string stuff in user space due to
all the make variable games we play), ext4_getattr() was something
like 1% of the time according to the profile I gathered. It might be
bogus - maybe the cacheline ends up being accessed later anyway, but
it _looked_ like it was the whole "i_extra_isize" access that missed
in the cache.

That's all for gathering the STATX_BTIME information, that the caller
doesn't even *want*.

How about a patch like the attached?

                 Linus