linux-kernel - Re: [PATCH] mm, page_alloc: fix build_zonerefs

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Date:   Thu, 7 Apr 2022 12:34:40 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     Juergen Gross <jgross@...e.com>
Cc:     xen-devel@...ts.xenproject.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        stable@...r.kernel.org,
        Marek Marczykowski-Górecki 
        <marmarek@...isiblethingslab.com>, Mel Gorman <mgorman@...e.de>
Subject: Re: [PATCH] mm, page_alloc: fix build_zonerefs_node()

Ccing Mel

On Thu 07-04-22 11:32:21, Juergen Gross wrote:
> Since commit 9d3be21bf9c0 ("mm, page_alloc: simplify zonelist
> initialization") only zones with free memory are included in a built
> zonelist. This is problematic when e.g. all memory of a zone has been
> ballooned out.

What is the actual problem there?

> Use populated_zone() when building a zonelist as it has been done
> before that commit.
> 
> Cc: stable@...r.kernel.org
> Fixes: 9d3be21bf9c0 ("mm, page_alloc: simplify zonelist initialization")

Did you mean to refer to 
6aa303defb74 ("mm, vmscan: only allocate and reclaim from zones with
pages managed by the buddy allocator")?

> Reported-by: Marek Marczykowski-Górecki <marmarek@...isiblethingslab.com>
> Signed-off-by: Juergen Gross <jgross@...e.com>
> ---
>  mm/page_alloc.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index bdc8f60ae462..3d0662af3289 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -6128,7 +6128,7 @@ static int build_zonerefs_node(pg_data_t *pgdat, struct zoneref *zonerefs)
>  	do {
>  		zone_type--;
>  		zone = pgdat->node_zones + zone_type;
> -		if (managed_zone(zone)) {
> +		if (populated_zone(zone)) {
>  			zoneref_set_zone(zone, &zonerefs[nr_zones++]);
>  			check_highest_zone(zone_type);
>  		}
> -- 
> 2.34.1

-- 
Michal Hocko
SUSE Labs