If vm_map_find() is asked to allocate a superpage-aligned region of virtual

addresses that is greater than a superpage in size but not a multiple of
the superpage size, then vm_map_find() is not always expanding the kernel
pmap to support the last few small pages being allocated.  These failures
are not commonplace, so this was first noticed by someone porting FreeBSD
to a new architecture.  Previously, we grew the kernel page table in
vm_map_findspace() when we found the first available virtual address.
This works most of the time because we always grow the kernel pmap or page
table by an amount that is a multiple of the superpage size.  Now, instead,
we defer the call to pmap_growkernel() until we are committed to a range
of virtual addresses in vm_map_insert().  In general, there is another
reason to prefer calling pmap_growkernel() in vm_map_insert().  It makes
it possible for someone to do the equivalent of an mmap(MAP_FIXED) on the
kernel map.

Reported by:	Svatopluk Kraus
Reviewed by:	kib@
MFC after:	3 weeks

0 files changed, 0 insertions, 0 deletions