Commit ed8f3f99 authored by Yang Yang's avatar Yang Yang Committed by Andrew Morton
Browse files

mm: workingset: update description of the source file 

The calculation of workingset size is the core logic of handling refault,
it had been updated several times[1][2] after workingset.c was created[3].
But the description hadn't been updated accordingly, this mismatch may
confuse the readers.  So we update the description to make it consistent
to the code.

[1] commit 34e58cac ("mm: workingset: let cache workingset challenge anon")
[2] commit aae466b0 ("mm/swap: implement workingset detection for anonymous LRU")
[3] commit a528910e ("mm: thrash detection-based file cache sizing")

Link: https://lkml.kernel.org/r/202304131634494948454@zte.com.cn


Signed-off-by: default avatarYang Yang <yang.yang29@zte.com.cn>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 1f6ab566

mm/workingset.c

+17 −6
Original line number Diff line number Diff line
@@ -111,9 +111,20 @@ 
 *

 *   NR_inactive + (R - E) <= NR_inactive + NR_active

 *

 * which can be further simplified to

 * If we have swap we should consider about NR_inactive_anon and

 * NR_active_anon, so for page cache and anonymous respectively:

 *

 *   (R - E) <= NR_active

 *   NR_inactive_file + (R - E) <= NR_inactive_file + NR_active_file

 *   + NR_inactive_anon + NR_active_anon

 *

 *   NR_inactive_anon + (R - E) <= NR_inactive_anon + NR_active_anon

 *   + NR_inactive_file + NR_active_file

 *

 * Which can be further simplified to:

 *

 *   (R - E) <= NR_active_file + NR_inactive_anon + NR_active_anon

 *

 *   (R - E) <= NR_active_anon + NR_inactive_file + NR_active_file

 *

 * Put into words, the refault distance (out-of-cache) can be seen as

 * a deficit in inactive list space (in-cache).  If the inactive list
@@ -130,14 +141,14 @@ 
 * are no longer in active use.

 *

 * So when a refault distance of (R - E) is observed and there are at

 * least (R - E) active pages, the refaulting page is activated

 * optimistically in the hope that (R - E) active pages are actually

 * least (R - E) pages in the userspace workingset, the refaulting page

 * is activated optimistically in the hope that (R - E) pages are actually

 * used less frequently than the refaulting page - or even not used at

 * all anymore.

 *

 * That means if inactive cache is refaulting with a suitable refault

 * distance, we assume the cache workingset is transitioning and put

 * pressure on the current active list.

 * pressure on the current workingset.

 *

 * If this is wrong and demotion kicks in, the pages which are truly

 * used more frequently will be reactivated while the less frequently
@@ -469,7 +480,7 @@ void workingset_refault(struct folio *folio, void *shadow) 
	 * don't activate pages that couldn't stay resident even if

	 * all the memory was available to the workingset. Whether

	 * workingset competition needs to consider anon or not depends

	 * on having swap.

	 * on having free swap space.

	 */

	workingset_size = lruvec_page_state(eviction_lruvec, NR_ACTIVE_FILE);

	if (!file) {