linux-kernel - Re: [PATCH] mm: vmscan : pgdemote vmstat is not getting updated when MGLRU is enabled.

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Message-ID: <e9e8c5d4-d891-a8c0-21a1-1916a49940c3@gmail.com>
Date: Sat, 11 Jan 2025 10:10:05 +0800
From: Li Zhijian <zhijianli88.lz@...il.com>
To: donettom@...ux.ibm.com
Cc: akpm@...ux-foundation.org, aneesh.kumar@...nel.org, hannes@...xchg.org,
 kaiyang2@...cmu.edu, linux-kernel@...r.kernel.org, linux-mm@...ck.org,
 mhocko@...nel.org, muchun.song@...ux.dev, rientjes@...gle.com,
 ritesh.list@...il.com, roman.gushchin@...ux.dev, shakeel.butt@...ux.dev,
 weixugc@...gle.com, yuzhao@...gle.com
Subject: Re: [PATCH] mm: vmscan : pgdemote vmstat is not getting updated when
 MGLRU is enabled.

> When MGLRU is enabled, the pgdemote_kswapd, pgdemote_direct, and
> pgdemote_khugepaged stats in vmstat are not being updated.
> 'Commit f77f0c751478 ("mm,memcg: provide per-cgroup counters for
> NUMA balancing operations")' moved the pgdemote vmstat update
> from demote_folio_list() to shrink_inactive_list(), which is in
> the normal LRU path. As a result, the pgdemote stats are updated
> correctly for the normal LRU but not for MGLRU.
> To address this, we have added the pgdemote stat update in the
> evict_folios() function, which is in the MGLRU path. With this
> patch, the pgdemote stats will now be updated correctly when MGLRU
> is enabled.
> Without this patch vmstat output when MGLRU is enabled
> ======================================================
> pgdemote_kswapd 0
> pgdemote_direct 0
> pgdemote_khugepaged 0
> With this patch vmstat output when MGLRU is enabled
> ===================================================
> pgdemote_kswapd 43234
> pgdemote_direct 4691
> pgdemote_khugepaged 0
> Fixes: f77f0c751478 ("mm,memcg: provide per-cgroup counters for NUMA balancing operations")
> Signed-off-by: Donet Tom <donettom@...ux.ibm.com>

Great minds think alike, It's excatly same with mine[0] :)

There is another bug[1] as well.

[0] https://lore.kernel.org/linux-mm/20250110122133.423481-2-lizhijian@fujitsu.com/

[1] https://lore.kernel.org/linux-mm/20250110122133.423481-1-lizhijian@fujitsu.com/

Feel free to add vvv if your patch is accepted at last.

Tested-by: Li Zhijian <lizhijian@...itsu.com>

Reviewed-by: Li Zhijian <lizhijian@...itsu.com>

> ---
>    mm/vmscan.c  <https://lore.kernel.org/lkml/20250109060540.451261-1-donettom@linux.ibm.com/#Z31mm:vmscan.c>  | 3 +++
>    1 filechanged  <https://lore.kernel.org/lkml/20250109060540.451261-1-donettom@linux.ibm.com/#related>, 3 insertions(+)
> diff <https://lore.kernel.org/lkml/20250109060540.451261-1-donettom@linux.ibm.com/#iZ31mm:vmscan.c> --git a/mm/vmscan.c b/mm/vmscan.c index 9a859b7d18d7..b1ec5ece067e 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -4642,6 +4642,9 @@ static int evict_folios(struct lruvec *lruvec, struct scan_control *sc, int swap   		reset_batch_size(walk);
>    	}
>    + __mod_lruvec_state(lruvec, PGDEMOTE_KSWAPD + reclaimer_offset(), + stat.nr_demoted); +   	item = PGSTEAL_KSWAPD + reclaimer_offset();
>    	if (!cgroup_reclaim(sc))
>    		__count_vm_events(item, reclaimed);
> --