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mm: workingset: update description of the source file

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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 34e58cac6d ("mm: workingset: let cache workingset challenge anon")
[2] commit aae466b005 ("mm/swap: implement workingset detection for anonymous LRU")
[3] commit a528910e12 ("mm: thrash detection-based file cache sizing")

Link: https://lkml.kernel.org/r/202304131634494948454@zte.com.cn
Signed-off-by: Yang Yang <yang.yang29@zte.com.cn>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Yang Yang 2023-04-13 16:34:49 +08:00 committed by Andrew Morton
parent 1f6ab566cb
commit ed8f3f999e
1 changed files with 17 additions and 6 deletions
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23
mm/workingset.c
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@ -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) {