Re: [PATCH v3] mm/bpf: Always flush memcg stats when explicitly requested

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential
issue to consider:
- [High] mm/bpf: single-word nickname in Author and Signed-off-by
  trailer
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commit 4c2af3a1c095e013e48cf708056b8f9ea3fe242a
Author: Runli <mingyu.he@shopee.com>

> mm/bpf: Always flush memcg stats when explicitly requested
>
> memcg_rstat_updated() stops walking the ancestors when a memcg exceeds
> the flush threshold. A concurrent flush can leave an ancestor below the
> threshold, so the early exit prevents it from receiving further updates.
>
> Consider root and leaf on a 4-CPU system, with a threshold of 256.
> CPU 0 is flushing another CPU's stats after CPU 1's stats have already
> been flushed. The counts below are shared stats_updates counters:
>
>   CPU 0 (root flush)                CPU 1 (leaf updates)
>   ------------------               --------------------
>   clear leaf->stats_updates
>                                    add 64 to leaf and root
>   clear root->stats_updates
>   finish flush
>                                    leaf = 64, root = 0
>                                    4 more batches of 64:
>                                      leaf = 320, root = 256
>                                    next update:
>                                      leaf > threshold
>                                      break; root is not updated
>
> Root remains at the threshold, which is insufficient to trigger a flush,
> while further leaf updates keep taking the early exit. The periodic
> forced flush restores progress, but until then the root's aggregated
> statistics can fall far behind. For example, page cache grows at rate of
> 1 GiB/s, a two-second wait can leave the reported usage about 2 GiB below
> the actual usage.
>
> Make bpf_mem_cgroup_flush_stats() force a flush without waiting for the
> periodic flusher, while preserving the memcg flush bookkeeping.
>
> Suggested-by: Shakeel Butt <shakeel.butt@linux.dev>
> Link: https://lore.kernel.org/all/avKy9oMwDRjKjfzm@linux.dev/
> Signed-off-by: Runli <mingyu.he@shopee.com>

[Severity: High]
Documentation/process/submitting-patches.rst requires a full real name
rather than a single-word nickname or handle in the Author header and
Signed-off-by trailer (for example, Mingyu He <mingyu.he@shopee.com>).

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Sashiko AI review · https://sashiko.dev/#/patchset/20261112041348.66915-1-mingyu.he@shopee.com?part=1