Re: [PATCH v3 1/2] mm/vmscan: mitigate spurious kswapd_failures reset from direct reclaim

2026/1/17 01:00, "Johannes Weiner" <hannes@cmpxchg.org mailto:hannes@cmpxchg.org?to=%22Johannes%20Weiner%22%20%3Channes%40cmpxchg.org%3E > wrote:

[...]

quoted

Great analysis, and I agree with both the fix and adding tracepoints.

Two minor nits:

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@@ -2650,6 +2650,25 @@ static bool can_age_anon_pages(struct lruvec *lruvec,
 lruvec_memcg(lruvec));
 }
 
 +static void pgdat_reset_kswapd_failures(pg_data_t *pgdat)
 +{
 + atomic_set(&pgdat->kswapd_failures, 0);
 +/*
 + * Reset kswapd_failures only when the node is balanced. Without this
 + * check, successful direct reclaim (e.g., from cgroup memory.high
 + * throttling) can keep resetting kswapd_failures even when the node
 + * cannot be balanced, causing kswapd to run endlessly.
 + */
 +static bool pgdat_balanced(pg_data_t *pgdat, int order, int highest_zoneidx);
 +static inline void pgdat_try_reset_kswapd_failures(struct pglist_data *pgdat,

Please remove the inline, the compiler will figure it out.

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+ struct scan_control *sc)
 +{
 + if (pgdat_balanced(pgdat, sc->order, sc->reclaim_idx))
 + pgdat_reset_kswapd_failures(pgdat);
 +}

As this is kswapd API, please move these down to after wakeup_kswapd().

I think we can streamline the names a bit. We already use "hopeless"
for that state in the comments; can you please rename the functions
kswapd_clear_hopeless() and kswapd_try_clear_hopeless()?

We should then also replace the open-coded kswapd_failure checks with
kswapd_test_hopeless(). But I can send a follow-up patch if you don't
want to, just let me know.

Thanks, Johannes and Shakeel. I'll send an updated version with these fixes.