linux-kernel - Re: [PATCH v2] mm, page_alloc: fix build_zonerefs

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Date:   Thu, 7 Apr 2022 14:45:57 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Juergen Gross <jgross@...e.com>, xen-devel@...ts.xenproject.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Cc:     Andrew Morton <akpm@...ux-foundation.org>, stable@...r.kernel.org,
        Marek Marczykowski-Górecki 
        <marmarek@...isiblethingslab.com>, Michal Hocko <mhocko@...e.com>
Subject: Re: [PATCH v2] mm, page_alloc: fix build_zonerefs_node()

On 07.04.22 14:06, Juergen Gross wrote:
> Since commit 6aa303defb74 ("mm, vmscan: only allocate and reclaim from
> zones with pages managed by the buddy allocator") 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 when zonelists are being
> rebuilt.
> 
> The decision whether to rebuild the zonelists when onlining new memory
> is done based on populated_zone() returning 0 for the zone the memory
> will be added to. The new zone is added to the zonelists only, if it
> has free memory pages (managed_zone() returns a non-zero value) after
> the memory has been onlined. This implies, that onlining memory will
> always free the added pages to the allocator immediately, but this is
> not true in all cases: when e.g. running as a Xen guest the onlined
> new memory will be added only to the ballooned memory list, it will be
> freed only when the guest is being ballooned up afterwards.
> 
> Another problem with using managed_zone() for the decision whether a
> zone is being added to the zonelists is, that a zone with all memory
> used will in fact be removed from all zonelists in case the zonelists
> happen to be rebuilt.
> 
> Use populated_zone() when building a zonelist as it has been done
> before that commit.
> 
> Cc: stable@...r.kernel.org
> Fixes: 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>
> Acked-by: Michal Hocko <mhocko@...e.com>
> ---
> V2:
> - updated commit message (Michal Hocko)
> ---
>  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);
>  		}

Did you drop my Ack?

Also, I'd appreciate getting CCed on patches where I commented.

-- 
Thanks,

David / dhildenb