mm: return zero_resv_unavail optimization

When checking for valid pfns in zero_resv_unavail(), it is not necessary
to verify that pfns within pageblock_nr_pages ranges are valid, only the
first one needs to be checked.  This is because memory for pages are
allocated in contiguous chunks that contain pageblock_nr_pages struct
pages.

Link: http://lkml.kernel.org/r/20181002143821.5112-3-msys.mizuma@gmail.com
Signed-off-by: Pavel Tatashin <pavel.tatashin@microsoft.com>
Signed-off-by: Masayoshi Mizuma <m.mizuma@jp.fujitsu.com>
Reviewed-by: Masayoshi Mizuma <m.mizuma@jp.fujitsu.com>
Acked-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 26 insertions, 20 deletions

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 6d863c5afa08..863d46da6586 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -6509,6 +6509,29 @@ void __init free_area_init_node(int nid, unsigned long *zones_size,
 }
 
 #if defined(CONFIG_HAVE_MEMBLOCK) && !defined(CONFIG_FLAT_NODE_MEM_MAP)
+
+/*
+ * Zero all valid struct pages in range [spfn, epfn), return number of struct
+ * pages zeroed
+ */
+static u64 zero_pfn_range(unsigned long spfn, unsigned long epfn)
+{
+        unsigned long pfn;
+        u64 pgcnt = 0;
+
+        for (pfn = spfn; pfn < epfn; pfn++) {
+                if (!pfn_valid(ALIGN_DOWN(pfn, pageblock_nr_pages))) {
+                        pfn = ALIGN_DOWN(pfn, pageblock_nr_pages)
+                                + pageblock_nr_pages - 1;
+                        continue;
+                }
+                mm_zero_struct_page(pfn_to_page(pfn));
+                pgcnt++;
+        }
+
+        return pgcnt;
+}
+
 /*
  * Only struct pages that are backed by physical memory are zeroed and
  * initialized by going through __init_single_page(). But, there are some
@@ -6524,7 +6547,6 @@ void __init free_area_init_node(int nid, unsigned long *zones_size,
 void __init zero_resv_unavail(void)
 {
         phys_addr_t start, end;
-        unsigned long pfn;
         u64 i, pgcnt;
         phys_addr_t next = 0;
 
@@ -6534,34 +6556,18 @@ void __init zero_resv_unavail(void)
         pgcnt = 0;
         for_each_mem_range(i, &memblock.memory, NULL,
                         NUMA_NO_NODE, MEMBLOCK_NONE, &start, &end, NULL) {
-                if (next < start) {
-                        for (pfn = PFN_DOWN(next); pfn < PFN_UP(start); pfn++) {
-                                if (!pfn_valid(ALIGN_DOWN(pfn, pageblock_nr_pages)))
-                                        continue;
-                                mm_zero_struct_page(pfn_to_page(pfn));
-                                pgcnt++;
-                        }
-                }
+                if (next < start)
+                        pgcnt += zero_pfn_range(PFN_DOWN(next), PFN_UP(start));
                 next = end;
         }
-        for (pfn = PFN_DOWN(next); pfn < max_pfn; pfn++) {
-                if (!pfn_valid(ALIGN_DOWN(pfn, pageblock_nr_pages)))
-                        continue;
-                mm_zero_struct_page(pfn_to_page(pfn));
-                pgcnt++;
-        }
-
+        pgcnt += zero_pfn_range(PFN_DOWN(next), max_pfn);
 
         /*
          * Struct pages that do not have backing memory. This could be because
          * firmware is using some of this memory, or for some other reasons.
-         * Once memblock is changed so such behaviour is not allowed: i.e.
-         * list of "reserved" memory must be a subset of list of "memory", then
-         * this code can be removed.
          */
         if (pgcnt)
                 pr_info("Zeroed struct page in unavailable ranges: %lld pages", pgcnt);
-
 }
 #endif /* CONFIG_HAVE_MEMBLOCK && !CONFIG_FLAT_NODE_MEM_MAP */