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

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Date:   Thu, 7 Apr 2022 14:53:37 +0200
From:   Juergen Gross <jgross@...e.com>
To:     David Hildenbrand <david@...hat.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 14:45, David Hildenbrand wrote:
> 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?

Oh, sorry for that.

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

Will do in future.


Juergen

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