pgdat_balanced

/*
 * pgdat_balanced() is used when checking if anode is balanced.
 *
 * For order-0, all zones must be balanced!
 *
 * For high-order allocations only zones thatmeet watermarks and are in a
 * zone allowed by the callers classzone_idxare added to balanced_pages. The
 * total of balanced pages must be at least 25%of the zones allowed by
 * classzone_idx for the node to be consideredbalanced. Forcing all zones to
 * be balanced for high orders can causeexcessive reclaim when there are
 * imbalanced zones.
 * The choice of 25% is due to
 *   o a16M DMA zone that is balanced will not balance a zone on any
 *    reasonable sized machine
 *   o Onall other machines, the top zone must be at least a reasonable
 *    percentage of the middle zones. For example, on 32-bit x86, highmem
 *    would need to be at least 256M for it to be balance a whole node.
 *    Similarly, on x86-64 the Normal zone would need to be at least 1G
 *     tobalance a node on its own. These seemed like reasonable ratios.
 */
static bool pgdat_balanced(pg_data_t *pgdat, int order, intclasszone_idx)
{
       unsigned long managed_pages = 0;
       unsigned long balanced_pages = 0;
       int i;
 
       /* Check the watermark levels */
       for(i = 0; i <= classzone_idx; i++) {
              struct zone *zone =pgdat->node_zones + i;
 
              if (!populated_zone(zone))
                     continue;
 
              managed_pages +=zone->managed_pages;
if (!zone_reclaimable(zone)) {
                     balanced_pages +=zone->managed_pages;
                     continue;
              }
 
if (zone_balanced(zone, order, false, 0, i))
                     balanced_pages +=zone->managed_pages;
              else if (!order)
                     return false;
       }
 
       if (order)
return balanced_pages >= (managed_pages >> 2);
       else
              return true;
}