On 3/9/21 9:41 AM, Oscar Salvador wrote:

When sizeof(struct page) is not a power of 2, sections do not span
a PMD anymore and so when populating them some parts of the PMD will
remain unused.
Because of this, PMDs will be left behind when depopulating sections
since remove_pmd_table() thinks that those unused parts are still in
use.

Fix this by marking the unused parts with PAGE_UNUSED, so memchr_inv()
will do the right thing and will let us free the PMD when the last user
of it is gone.

This patch is based on a similar patch by David Hildenbrand:

https://lore.kernel.org/linux-mm/20200722094558.9828-9-david@redhat.com/ (local)

Looks good now.  It's much easier to read without the optimization.

Acked-by: Dave Hansen <dave.hansen@linux.intel.com>