On Sun, Dec 31, 2023 at 12:40:40PM -0800, Darrick J. Wong wrote: > From: Darrick J. Wong <djwong@xxxxxxxxxx> > > Mapping a page into the kernel's address space is expensive. What do you mean with mapping into the kernel's address space? Mormally that owuld point to the kmap* family of helpers, but those are complete no-ops on the typical xfs setups without highmem. But even with highmem at least kmap_local_page isn't too expensive. My xfile diet patches actually change the xfile mapping to never allocate highmem, which simplifies things a bit (and fixes a bug in the xfs_buf use that just uses page_address instead of a kmap). So I suspect this is something else and more about looking up pages?
