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

[Vlastimil Babka <vbabka@suse.cz>]

+ CC folks who focus on reclaim

On 3/4/20 9:32 PM, Adam Jackson wrote:
> 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;
>  			}
>