linux-kernel - Re: [PATCH v3 1/2] mm/vmscan: mitigate spurious kswapd

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Message-ID: <562a3b0db8bed7a1f13c3e1b8ccc846181226b5b@linux.dev>
Date: Mon, 19 Jan 2026 03:04:16 +0000
From: "Jiayuan Chen" <jiayuan.chen@...ux.dev>
To: "Johannes Weiner" <hannes@...xchg.org>
Cc: linux-mm@...ck.org, shakeel.butt@...ux.dev, "Jiayuan Chen"
 <jiayuan.chen@...pee.com>, "Andrew Morton" <akpm@...ux-foundation.org>,
 "David Hildenbrand" <david@...nel.org>, "Lorenzo Stoakes"
 <lorenzo.stoakes@...cle.com>, "Liam R. Howlett"
 <Liam.Howlett@...cle.com>, "Vlastimil Babka" <vbabka@...e.cz>, "Mike
 Rapoport" <rppt@...nel.org>, "Suren Baghdasaryan" <surenb@...gle.com>,
 "Michal Hocko" <mhocko@...e.com>, "Axel Rasmussen"
 <axelrasmussen@...gle.com>, "Yuanchu Xie" <yuanchu@...gle.com>, "Wei Xu"
 <weixugc@...gle.com>, "Steven Rostedt" <rostedt@...dmis.org>, "Masami
 Hiramatsu" <mhiramat@...nel.org>, "Mathieu Desnoyers"
 <mathieu.desnoyers@...icios.com>, "Brendan Jackman"
 <jackmanb@...gle.com>, "Zi Yan" <ziy@...dia.com>, "Qi Zheng"
 <zhengqi.arch@...edance.com>, linux-kernel@...r.kernel.org,
 linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/2] mm/vmscan: mitigate spurious kswapd_failures
 reset from direct reclaim

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

[...]
> > 
> Great analysis, and I agree with both the fix and adding tracepoints.
> 
> Two minor nits:
> 
> > 
> > @@ -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.
> 
> > 
> > + 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.