[IA64] Make show_mem() skip holes in a pgdat

This patch modifies ia64's show_mem() to walk the vmem_map page tables and
rapidly skip forward across regions where the page tables are missing.
This prevents the pfn_valid() check from causing numerous unnecessary
page faults.

Without this patch on a 512 node 512 cpu system where every node has four
memory holes, the show_mem() call takes 1 hour 18 minutes.  With this
patch, it takes less than 3 seconds.

Signed-off-by: Robin Holt <holt@sgi.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>

1 files changed, 65 insertions, 1 deletions

diff --git a/arch/ia64/mm/discontig.c b/arch/ia64/mm/discontig.c
index ec9eeb89975d..b6bcc9fa3603 100644
--- a/arch/ia64/mm/discontig.c
+++ b/arch/ia64/mm/discontig.c
@@ -519,6 +519,68 @@ void __cpuinit *per_cpu_init(void)
 }
 #endif /* CONFIG_SMP */
 
+#ifdef CONFIG_VIRTUAL_MEM_MAP
+static inline int find_next_valid_pfn_for_pgdat(pg_data_t *pgdat, int i)
+{
+        unsigned long end_address, hole_next_pfn;
+        unsigned long stop_address;
+
+        end_address = (unsigned long) &vmem_map[pgdat->node_start_pfn + i];
+        end_address = PAGE_ALIGN(end_address);
+
+        stop_address = (unsigned long) &vmem_map[
+                pgdat->node_start_pfn + pgdat->node_spanned_pages];
+
+        do {
+                pgd_t *pgd;
+                pud_t *pud;
+                pmd_t *pmd;
+                pte_t *pte;
+
+                pgd = pgd_offset_k(end_address);
+                if (pgd_none(*pgd)) {
+                        end_address += PGDIR_SIZE;
+                        continue;
+                }
+
+                pud = pud_offset(pgd, end_address);
+                if (pud_none(*pud)) {
+                        end_address += PUD_SIZE;
+                        continue;
+                }
+
+                pmd = pmd_offset(pud, end_address);
+                if (pmd_none(*pmd)) {
+                        end_address += PMD_SIZE;
+                        continue;
+                }
+
+                pte = pte_offset_kernel(pmd, end_address);
+retry_pte:
+                if (pte_none(*pte)) {
+                        end_address += PAGE_SIZE;
+                        pte++;
+                        if ((end_address < stop_address) &&
+                            (end_address != ALIGN(end_address, 1UL << PMD_SHIFT)))
+                                goto retry_pte;
+                        continue;
+                }
+                /* Found next valid vmem_map page */
+                break;
+        } while (end_address < stop_address);
+
+        end_address = min(end_address, stop_address);
+        end_address = end_address - (unsigned long) vmem_map + sizeof(struct page) - 1;
+        hole_next_pfn = end_address / sizeof(struct page);
+        return hole_next_pfn - pgdat->node_start_pfn;
+}
+#else
+static inline int find_next_valid_pfn_for_pgdat(pg_data_t *pgdat, int i)
+{
+        return i + 1;
+}
+#endif
+
 /**
  * show_mem - give short summary of memory stats
  *
@@ -547,8 +609,10 @@ void show_mem(void)
                         struct page *page;
                         if (pfn_valid(pgdat->node_start_pfn + i))
                                 page = pfn_to_page(pgdat->node_start_pfn + i);
-                        else
+                        else {
+                                i = find_next_valid_pfn_for_pgdat(pgdat, i) - 1;
                                 continue;
+                        }
                         if (PageReserved(page))
                                 reserved++;
                         else if (PageSwapCache(page))