On Thu, Feb 03, 2022 at 10:27:11AM +0100, Michal Hocko wrote:
>On Thu 03-02-22 02:00:22, Wei Yang wrote:
>> During memory hotplug, when online/offline a zone, we need to rebuild
>> the zonelist for all nodes. Current behavior would lose a valid zone in
>> zonelist since only pick up managed_zone.
>>
>> There are two cases for a zone with memory but still !managed.
>>
>> * all pages were allocated via memblock
>> * all pages were taken by ballooning / virtio-mem
>>
>> This state maybe temporary, since both of them may release some memory.
>> Then it end up with a managed zone not in zonelist.
>>
>> This is introduced in 'commit 6aa303defb74 ("mm, vmscan: only allocate
>> and reclaim from zones with pages managed by the buddy allocator")'.
>> This patch restore the behavior.
>
>It has been introduced to fix a problem described in the the changelog
>(FADUMP configuration making kswapd hogging a cpu). You are not
>explaining why the original issue is not possible after this change.
>
The first sight is kswapd deals with pgdat->node_zones, which is not affected
by pgdat->node_zonelists.
For the exact detail, I don't figure that out now. Will need some time to take
a look into. For that commit, I only found this link.
http://lkml.kernel.org/r/20160831195104.GB8119@xxxxxxxxxxxxxxxxxxx If there
are some other discussions, it would be helpful.
>I also think that this is more of theoretical issue than anything that
>is a real life concern. It is good to state that in the changelog as
>well.
>
>That being said I am not against the change but the changelog needs more
>explanation before I can ack it.
>
>> Signed-off-by: Wei Yang <richard.weiyang@xxxxxxxxx>
>> CC: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
>> CC: David Hildenbrand <david@xxxxxxxxxx>
>> Fixes: 6aa303defb74 ("mm, vmscan: only allocate and reclaim from zones with pages managed by the buddy allocator")
>
>Fixes tag should be really used only if the referenced commit breaks
>something. I do not really see this to be the case here.
>
Got it.
>Thanks!
>
>> ---
>> 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 de15021a2887..b433a57ee76f 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -6092,7 +6092,7 @@ 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);
>> }
>> --
>> 2.33.1
>
>--
>Michal Hocko
>SUSE Labs
--
Wei Yang
Help you, Help me
