vm_phys: fix freelist_contig
vm_phys_find_freelist_contig is called to search a list of max-sized
free page blocks and find one that, when joined with adjacent blocks
in memory, can satisfy a request for a memory allocation bigger than
any single max-sized free page block. In commit
fa8a6585c7522b7de6d29802967bd5eba2f2dcf1, I defined this function in
order to offer two improvements: 1) reduce the worst-case search time,
and 2) allow solutions that include less-than max-sized free page
blocks at the front or back of the giant allocation. However, it turns
out that this change introduced an error, reported in In Bug
- That error concerns failing to check segment boundaries. This
change fixes an error in vm_phys_find_freelist_config that resolves
that bug. It also abandons improvement 2), because the value of that
improvement is small and because preserving it would require more
testing than I am able to do.
PR: 274592
Reported by: shafaisal.us@gmail.com
Reviewed by: alc, markj
Tested by: shafaisal.us@gmail.com
Fixes: fa8a6585c752 vm_phys: avoid waste in multipage allocation
MFC after: 10 days
Differential Revision: https://reviews.freebsd.org/D42509
Approved by: so
Security: FreeBSD-EN-23:20.vm
(cherry picked from commit 2a4897bd4e1bd8430d955abd3cf6675956bb9d61)
(cherry picked from commit 210fce73ae0e4106a3aeb1970ffbeb30d0baa6ba)