[PATCH] mm/vmscan: Prioritize anonymous executable pages like we do file-backed

[Adam Jackson <ajax@redhat.com>]

The page reclamation scanner tries to keep executable pages resident,
since taking a hard page fault to satisfy an icache miss is really not
great for interactivity.  Anonymous executable pages tend to contain
code that has been just-in-time compiled for performance reasons. By
requiring that executable pages be file-backed, we're putting possibly
the most performance-sensitive code at higher risk of eviction, which
seems backwards.

On an amd64 machine running Fedora 31, the firefox I happen to have
running requires about 89M of file-backed text and 12M of anonymous text
for 30 open tabs. The next largest process in terms of anonymous text is
gnome-shell, with 1M anonymous and 57M file-backed. No other process had
significant anonymous text, most had none. Penalizing those 13M
specifically when under memory pressure seems like an easy hazard to
avoid.

Signed-off-by: Adam Jackson <ajax@redhat.com>
---
 mm/vmscan.c | 11 ++++-------
 1 file changed, 4 insertions(+), 7 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index ee4eecc7e1c2..9bfbc30d61d8 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2095,15 +2095,12 @@ static void shrink_active_list(unsigned long nr_to_scan,
 				    &vm_flags)) {
 			nr_rotated += hpage_nr_pages(page);
 			/*
-			 * Identify referenced, file-backed active pages and
-			 * give them one more trip around the active list. So
+			 * Identify referenced, executable active pages and
+			 * give them one more trip around the active list, so
 			 * that executable code get better chances to stay in
-			 * memory under moderate memory pressure.  Anon pages
-			 * are not likely to be evicted by use-once streaming
-			 * IO, plus JVM can create lots of anon VM_EXEC pages,
-			 * so we ignore them here.
+			 * memory under moderate memory pressure.
 			 */
-			if ((vm_flags & VM_EXEC) && page_is_file_cache(page)) {
+			if ((vm_flags & VM_EXEC)) {
 				list_add(&page->lru, &l_active);
 				continue;
 			}
-- 
2.23.0