Re: [PATCH v2] mm, page_alloc: fix build_zonerefs_node()

[Juergen Gross <jgross@xxxxxxxx>]

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@xxxxxxxxxxxxxxx
> > Fixes: 6aa303defb74 ("mm, vmscan: only allocate and reclaim from zones with pages 
> > managed by the buddy allocator")
> > Reported-by: Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>
> > Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> > Acked-by: Michal Hocko <mhocko@xxxxxxxx>
> > ---
> > 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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