Push down the responsibility for zeroing a physical page from the

caller to vm_page_grab().  Although this gives VM_ALLOC_ZERO a
different meaning for vm_page_grab() than for vm_page_alloc(), I feel
such change is necessary to accomplish other goals.  Specifically, I
want to make the PG_ZERO flag immutable between the time it is
allocated by vm_page_alloc() and freed by vm_page_free() or
vm_page_free_zero() to avoid locking overheads.  Once we gave up on
the ability to automatically recognize a zeroed page upon entry to
vm_page_free(), the ability to mutate the PG_ZERO flag became useless.
Instead, I would like to say that "Once a page becomes valid, its
PG_ZERO flag must be ignored."

1 files changed, 2 insertions, 0 deletions

diff --git a/sys/vm/vm_page.c b/sys/vm/vm_page.c
index 789ad98..45e3fc9 100644
--- a/sys/vm/vm_page.c
+++ b/sys/vm/vm_page.c
@@ -1460,6 +1460,8 @@ retrylookup:
 			return NULL;
 		goto retrylookup;
 	}
+	if (allocflags & VM_ALLOC_ZERO && (m->flags & PG_ZERO) == 0)
+		pmap_zero_page(m);
 
 	return m;
 }