git: 0b3bc7288984 - main - amd64 pmap: adjust the empty pmap optimization in pmap_remove()

The branch main has been updated by kib:

URL: https://cgit.FreeBSD.org/src/commit/?id=0b3bc7288984c17da00d9f8c29f116d56bf44d35

commit 0b3bc7288984c17da00d9f8c29f116d56bf44d35
Author:     Konstantin Belousov <kib@FreeBSD.org>
AuthorDate: 2021-10-20 20:30:34 +0000
Commit:     Konstantin Belousov <kib@FreeBSD.org>
CommitDate: 2021-10-28 19:01:58 +0000

    amd64 pmap: adjust the empty pmap optimization in pmap_remove()
    
    to match the added accounting of the top-level page table pages.
    
    Reviewed by:    markj
    Tested by:      markj
    Sponsored by:   The FreeBSD Foundation
    MFC after:      1 week
    Differential revision:  https://reviews.freebsd.org/D32569
---
 sys/amd64/amd64/pmap.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/sys/amd64/amd64/pmap.c b/sys/amd64/amd64/pmap.c
index 1c4e8b3354fc..8526cc3031d2 100644
--- a/sys/amd64/amd64/pmap.c
+++ b/sys/amd64/amd64/pmap.c
@@ -6278,9 +6278,14 @@ pmap_remove(pmap_t pmap, vm_offset_t sva, vm_offset_t eva)
 	PG_V = pmap_valid_bit(pmap);
 
 	/*
+	 * If there are no resident pages besides the top level page
+	 * table page(s), there is nothing to do.  Kernel pmap always
+	 * accounts whole preloaded area as resident, which makes its
+	 * resident count > 2.
 	 * Perform an unsynchronized read.  This is, however, safe.
 	 */
-	if (pmap->pm_stats.resident_count == 0)
+	if (pmap->pm_stats.resident_count <= 1 + (pmap->pm_pmltopu != NULL ?
+	    1 : 0))
 		return;
 
 	anyvalid = 0;