Re: [PATCH] mm/vmscan: fix missing NR_ISOLATED counter update in MGLRU reclaim path

[Kairui Song <ryncsn@gmail.com>]

On Tue, Aug 11, 2026 at 03:17:03PM +0800, Hui Zhu wrote:
> From: Hui Zhu <zhuhui@kylinos.cn>
> 
> The MGLRU evict_folios() isolates folios from the LRU without updating
> NR_ISOLATED_ANON/FILE counters, unlike the legacy shrink_inactive_list()
> path.
> This causes compaction's too_many_isolated() check and the OOMkiller to
> under-count isolated pages when MGLRU reclaim is active, potentially
> leading to unnecessary compaction attempts or incorrect OOM decisions
> under memory pressure.

This patch still doesn't cover the OOM problem, too_many_isolated is not
used for MGLRU. I prefer to keep unifying them like what we did previously
with writeback.

It might work for compaction though, did you test it?

> 
> Add NR_ISOLATED counter updates in evict_folios(): increment after
> isolate_folios() and decrement after all retry passes complete, using
> the original isolated count saved before retry.
> 
> Signed-off-by: Hui Zhu <zhuhui@kylinos.cn>
> ---
>  mm/vmscan.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index bc324e37c5f1..723b513574b3 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -4817,6 +4817,7 @@ static int evict_folios(unsigned long nr_to_scan, struct lruvec *lruvec,
>  	struct lru_gen_mm_walk *walk;
>  	int scanned, reclaimed;
>  	int isolated = 0, type, type_scanned;
> +	int isolated_orig = 0;

The variable name looks a bit confusing, and what is your based commit?
In latest mm-unstable there is already a nr_isolated you can use.