Re: [PATCH v4 0/4] mm: workingset: fix the shadow node budget under MGLRU

[Andrew Morton]

On Tue,  8 Sep 2026 11:41:10 +0800 Hui Zhu <hui.zhu@xxxxxxxxx> wrote:

> From: Hui Zhu <zhuhui@xxxxxxxxxx>
> 
> Commit 7404bd37cfbe ("mm: workingset: use lruvec_lru_size() to get the
> number of lru pages") broke the workingset shadow node budget under
> MGLRU: lruvec_lru_size() reads mz->lru_zone_size, which MGLRU never
> maintains, so count_shadow_nodes() sees the evictable LRU lists as
> empty and the shadow shrinker reclaims eviction tokens almost as fast
> as they are created, losing thrashing protection.
> 
> ...
>
> Performance testing
> ===================
> 
> The test script and the raw results are available at [1].
> 
> Environment: 10-vCPU QEMU guest, 8 GiB RAM, cgroup v2; 7 runs per
> configuration, medians reported.  Workloads:
> 
>   w1-anon-churn: single-threaded anon fault/charge loop in a memcg
>                  (MADV_DONTNEED + re-fault, no reclaim).  Every touch
>                  is a real fault with charge and memcg stat updates,
>                  so it stresses exactly the fast path patch 1 changes.
>   w2-file-churn: file read loop under memory.high pressure
>                  (reclaim-bound, noisier).
>   w3-reparent:   reparent accounting sanity check.
> 
> w1-anon-churn (pages/s):
> 
>                  classic LRU          MGLRU
> base             4393028              4377122
> patches 1-2      4385996   (-0.2%)    4352887   (-0.6%)
> patches 1-3      4381832   (-0.3%)    4377053   (+0.0%)
> 
> w2-file-churn (MB/s):
> 
>                  classic LRU          MGLRU
> base             8277                 8226
> patches 1-2      8226      (-0.6%)    8123      (-1.3%)
> patches 1-3      8157      (-1.4%)    8294      (+0.8%)

Am I misinterpreting this?  This difference is probably within
inter-run variability?