Re: [PATCH v4 11/17] mm/madvise: adapt for LRU refs based operations for MGLRU

[sashiko-bot@kernel.org]

> From: Kairui Song <kasong@tencent.com>
> 
> For the active/inactive LRU, madvise clears PG_referenced so that one more
> access is not enough to reactivate a folio, and keeps PG_workingset on a
> folio demoted out of the active list so its refault is still accounted as
> a workingset refault (PSI).
> 
> MGLRU keeps that history in the folio's refs count instead, which now
> lives in PG_referenced, PG_workingset and LRU_REFS_MASK, so writing to
> those bits directly corrupts the count. The two hints want different
> things:
> 
> - MADV_COLD resets the count in folio_deactivate(), which also moves the
>   folio to the oldest generation.
> - MADV_PAGEOUT caps the count at LRU_REFS_WORKINGSET before handing the
>   folio to reclaim_pages(). The hint marks the folio as cold, so the
>   eviction shadow records the capped count and does not inflate the
>   eviction/refault counters of the hot tiers that drive aging, while
>   folios at or above the workingset threshold keep their PSI
>   classification.
> 
> PG_young is cleared for both LRUs as before, so the referenced walk does
> not count stale history as a recent access.
> 
> Signed-off-by: Kairui Song <kasong@tencent.com>

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

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Sashiko AI review · https://sashiko.dev/#/patchset/20261016-mglru-fg-v4-0-2106750c0bfa@tencent.com?part=11