Re: [PATCH v4 16/17] mm/mglru: make folio_test_workingset() work based on folio LRU refs

[sashiko-bot@kernel.org]

> From: Kairui Song <kasong@tencent.com>
> 
> folio_test_workingset() currently tests the PG_workingset bit, which
> is only the second lowest access bit of the folio LRU refs count now.
> Folios with a higher refs count carry it in the LRU_REFS_MASK field
> and no longer have PG_workingset set, so the bit test misses them.
> 
> folio_set_workingset() currently sets the PG_workingset bit with a
> plain set_bit(), which also over-promotes folios at a higher refs
> count: e.g. a folio at refs 4 is bumped to refs 6, advancing it
> toward LRU_REFS_MAX and an unintended generation promotion on the
> next access.
> 
> Move the test into mm_inline.h as an inline helper based on
> folio_lru_refs(), checking refs >= LRU_REFS_WORKINGSET.  The set
> stays a plain PG_workingset bit operation reserved for the
> classical LRU: under MGLRU the refs count is maintained by
> folio_inc_lru_refs(), and now triggers a debug WARN when called
> while MGLRU is fully on (the switching window is exempt, as the
> classical paths legitimately run alongside MGLRU then).  The one
> PageWorkingset() user in erofs is converted to the folio helper.
> 
> Under the classical LRU the refs count is not maintained, so the
> test falls back to the PG_workingset bit test, which is the old
> behavior.
> 
> Tested-by: zhaozhengzhuo <zhaozhengzhuo@uniontech.com>
> Signed-off-by: Kairui Song <kasong@tencent.com>

Sashiko has reviewed this patch and found no issues. It looks great!

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261016-mglru-fg-v4-0-2106750c0bfa@tencent.com?part=16