On Thu 20-07-17 08:55:42, Vlastimil Babka wrote:
> On 07/14/2017 10:00 AM, Michal Hocko wrote:
> > From: Michal Hocko <mhocko@xxxxxxxx>
> >
> > build_zonelists gradually builds zonelists from the nearest to the most
> > distant node. As we do not know how many populated zones we will have in
> > each node we rely on the _zoneref to terminate initialized part of the
> > zonelist by a NULL zone. While this is functionally correct it is quite
> > suboptimal because we cannot allow updaters to race with zonelists
> > users because they could see an empty zonelist and fail the allocation
> > or hit the OOM killer in the worst case.
> >
> > We can do much better, though. We can store the node ordering into an
> > already existing node_order array and then give this array to
> > build_zonelists_in_node_order and do the whole initialization at once.
> > zonelists consumers still might see halfway initialized state but that
> > should be much more tolerateable because the list will not be empty and
> > they would either see some zone twice or skip over some zone(s) in the
> > worst case which shouldn't lead to immediate failures.
> >
> > This patch alone doesn't introduce any functional change yet, though, it
> > is merely a preparatory work for later changes.
> >
> > Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
>
> I've collected the fold-ups from this thread and looked at the result as
> single patch. Sems OK, just two things:
> - please rename variable "i" in build_zonelists() to e.g. "nr_nodes"
> - the !CONFIG_NUMA variant of build_zonelists() won't build, because it
> doesn't declare nr_zones variable
Thanks! I will fold this in.
---
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index c0d3e8eeb150..6f192405e469 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -4957,7 +4957,7 @@ static void build_thisnode_zonelists(pg_data_t *pgdat)
static void build_zonelists(pg_data_t *pgdat)
{
static int node_order[MAX_NUMNODES];
- int node, load, i = 0;
+ int node, load, nr_nodes = 0;
nodemask_t used_mask;
int local_node, prev_node;
@@ -4978,12 +4978,12 @@ static void build_zonelists(pg_data_t *pgdat)
node_distance(local_node, prev_node))
node_load[node] = load;
- node_order[i++] = node;
+ node_order[nr_nodes++] = node;
prev_node = node;
load--;
}
- build_zonelists_in_node_order(pgdat, node_order, i);
+ build_zonelists_in_node_order(pgdat, node_order, nr_nodes);
build_thisnode_zonelists(pgdat);
}
@@ -5013,10 +5013,11 @@ static void build_zonelists(pg_data_t *pgdat)
{
int node, local_node;
struct zoneref *zonerefs;
+ int nr_zones;
local_node = pgdat->node_id;
- zonrefs = pgdat->node_zonelists[ZONELIST_FALLBACK]._zonerefs;
+ zonerefs = pgdat->node_zonelists[ZONELIST_FALLBACK]._zonerefs;
nr_zones = build_zonerefs_node(pgdat, zonerefs);
zonerefs += nr_zones;
--
Michal Hocko
SUSE Labs
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