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SubjectRe: [PATCH 6/9] mm, page_alloc: simplify zonelist initialization
On Fri 14-07-17 15:18:23, Mel Gorman wrote:
> On Fri, Jul 14, 2017 at 03:02:42PM +0200, Michal Hocko wrote:
[...]
> > What do you think about this on top?
> > ---
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index 49bade7ff049..3b98524c04ec 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -4913,20 +4913,21 @@ static int find_next_best_node(int node, nodemask_t *used_node_mask)
> > * This results in maximum locality--normal zone overflows into local
> > * DMA zone, if any--but risks exhausting DMA zone.
> > */
> > -static void build_zonelists_in_node_order(pg_data_t *pgdat, int *node_order)
> > +static void build_zonelists_in_node_order(pg_data_t *pgdat, int *node_order,
> > + unsigned nr_nodes)
> > {
> > struct zonelist *zonelist;
> > - int i, zoneref_idx = 0;
> > + int i, nr_zones = 0;
> >
> > zonelist = &pgdat->node_zonelists[ZONELIST_FALLBACK];
> >
> > - for (i = 0; i < MAX_NUMNODES; i++) {
> > + for (i = 0; i < nr_nodes; i++) {
>
> The first iteration is then -- for (i = 0; i < 0; i++)

find_next_best_node always returns at least one node (the local one) so
I believe that nr_nodes should never be 0.

> Fairly sure that's not what you meant.
>
>
> > pg_data_t *node = NODE_DATA(node_order[i]);
> >
> > - zoneref_idx = build_zonelists_node(node, zonelist, zoneref_idx);
> > + nr_zones = build_zonelists_node(node, zonelist, nr_zones);
>
> I meant converting build_zonelists_node and passing in &nr_zones and
> returning false when an empty node is encountered. In this context,
> it's also not about zones, it really is nr_zonerefs. Rename nr_zones in
> build_zonelists_node as well.

hmm, why don't we rather make it zonerefs based then. Something
like the following?
---
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 3b98524c04ec..01e67e629351 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -4772,18 +4772,17 @@ static void zoneref_set_zone(struct zone *zone, struct zoneref *zoneref)
*
* Add all populated zones of a node to the zonelist.
*/
-static int build_zonelists_node(pg_data_t *pgdat, struct zonelist *zonelist,
- int nr_zones)
+static int build_zonerefs_node(pg_data_t *pgdat, struct zoneref *zonerefs)
{
struct zone *zone;
enum zone_type zone_type = MAX_NR_ZONES;
+ int nr_zones = 0;

do {
zone_type--;
zone = pgdat->node_zones + zone_type;
if (managed_zone(zone)) {
- zoneref_set_zone(zone,
- &zonelist->_zonerefs[nr_zones++]);
+ zoneref_set_zone(zone, &zonerefs[nr_zones++]);
check_highest_zone(zone_type);
}
} while (zone_type);
@@ -4916,18 +4915,21 @@ static int find_next_best_node(int node, nodemask_t *used_node_mask)
static void build_zonelists_in_node_order(pg_data_t *pgdat, int *node_order,
unsigned nr_nodes)
{
- struct zonelist *zonelist;
- int i, nr_zones = 0;
+ struct zoneref *zonerefs;
+ int i;

- zonelist = &pgdat->node_zonelists[ZONELIST_FALLBACK];
+ zonerefs = pgdat->node_zonelists[ZONELIST_FALLBACK]._zonerefs;

for (i = 0; i < nr_nodes; i++) {
+ int nr_zones;
+
pg_data_t *node = NODE_DATA(node_order[i]);

- nr_zones = build_zonelists_node(node, zonelist, nr_zones);
+ nr_zones = build_zonerefs_node(node, zonerefs);
+ zonerefs += nr_zones;
}
- zonelist->_zonerefs[nr_zones].zone = NULL;
- zonelist->_zonerefs[nr_zones].zone_idx = 0;
+ zonerefs->zone = NULL;
+ zonerefs->zone_idx = 0;
}

/*
@@ -4935,13 +4937,14 @@ static void build_zonelists_in_node_order(pg_data_t *pgdat, int *node_order,
*/
static void build_thisnode_zonelists(pg_data_t *pgdat)
{
- struct zonelist *zonelist;
- int nr_zones = 0;
+ struct zoneref *zonerefs;
+ int nr_zones;

- zonelist = &pgdat->node_zonelists[ZONELIST_NOFALLBACK];
- nr_zones = build_zonelists_node(pgdat, zonelist, nr_zones);
- zonelist->_zonerefs[nr_zones].zone = NULL;
- zonelist->_zonerefs[nr_zones].zone_idx = 0;
+ zonerefs = pgdat->node_zonelists[ZONELIST_NOFALLBACK]._zonerefs;
+ nr_zones = build_zonerefs_node(pgdat, zonerefs);
+ zonerefs += nr_zones;
+ zonerefs->zone = NULL;
+ zonerefs->zone_idx = 0;
}

/*
@@ -5009,13 +5012,13 @@ static void setup_min_slab_ratio(void);
static void build_zonelists(pg_data_t *pgdat)
{
int node, local_node;
- enum zone_type j;
- struct zonelist *zonelist;
+ struct zoneref *zonerefs;

local_node = pgdat->node_id;

- zonelist = &pgdat->node_zonelists[ZONELIST_FALLBACK];
- j = build_zonelists_node(pgdat, zonelist, 0);
+ zonrefs = pgdat->node_zonelists[ZONELIST_FALLBACK]._zonerefs;
+ nr_zones = build_zonerefs_node(pgdat, zonerefs);
+ zonerefs += nr_zones;

/*
* Now we build the zonelist so that it contains the zones
@@ -5028,16 +5031,18 @@ static void build_zonelists(pg_data_t *pgdat)
for (node = local_node + 1; node < MAX_NUMNODES; node++) {
if (!node_online(node))
continue;
- j = build_zonelists_node(NODE_DATA(node), zonelist, j);
+ nr_zones = build_zonerefs_node(NODE_DATA(node), zonerefs);
+ zonerefs += nr_zones;
}
for (node = 0; node < local_node; node++) {
if (!node_online(node))
continue;
- j = build_zonelists_node(NODE_DATA(node), zonelist, j);
+ nr_zones = build_zonerefs_node(NODE_DATA(node), zonerefs);
+ zonerefs += nr_zones;
}

- zonelist->_zonerefs[j].zone = NULL;
- zonelist->_zonerefs[j].zone_idx = 0;
+ zonerefs->zone = NULL;
+ zonerefs->zone_idx = 0;
}

#endif /* CONFIG_NUMA */
--
Michal Hocko
SUSE Labs

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