mm: meminit: initialise a subset of struct pages if CONFIG_DEFERRED_STRUCT_PAGE_INIT is set

This patch initalises all low memory struct pages and 2G of the highest
zone on each node during memory initialisation if
CONFIG_DEFERRED_STRUCT_PAGE_INIT is set.  That config option cannot be set
but will be available in a later patch.  Parallel initialisation of struct
page depends on some features from memory hotplug and it is necessary to
alter alter section annotations.

Signed-off-by: Mel Gorman <mgorman@suse.de>
Tested-by: Nate Zimmer <nzimmer@sgi.com>
Tested-by: Waiman Long <waiman.long@hp.com>
Tested-by: Daniel J Blueman <daniel@numascale.com>
Acked-by: Pekka Enberg <penberg@kernel.org>
Cc: Robin Holt <robinmholt@gmail.com>
Cc: Nate Zimmer <nzimmer@sgi.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Waiman Long <waiman.long@hp.com>
Cc: Scott Norton <scott.norton@hp.com>
Cc: "Luck, Tony" <tony.luck@intel.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

3 files changed, 111 insertions, 3 deletions

diff --git a/mm/Kconfig b/mm/Kconfig
index c180af880ed5..e79de2bd12cd 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -636,3 +636,21 @@ config MAX_STACK_SIZE_MB
           changed to a smaller value in which case that is used.
 
           A sane initial value is 80 MB.
+
+# For architectures that support deferred memory initialisation
+config ARCH_SUPPORTS_DEFERRED_STRUCT_PAGE_INIT
+        bool
+
+config DEFERRED_STRUCT_PAGE_INIT
+        bool "Defer initialisation of struct pages to kswapd"
+        default n
+        depends on ARCH_SUPPORTS_DEFERRED_STRUCT_PAGE_INIT
+        depends on MEMORY_HOTPLUG
+        help
+          Ordinarily all struct pages are initialised during early boot in a
+          single thread. On very large machines this can take a considerable
+          amount of time. If this option is set, large machines will bring up
+          a subset of memmap at boot and then initialise the rest in parallel
+          when kswapd starts. This has a potential performance impact on
+          processes running early in the lifetime of the systemm until kswapd
+          finishes the initialisation.
diff --git a/mm/internal.h b/mm/internal.h
index 58e9022e3757..88ac7be741ca 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -387,6 +387,24 @@ static inline void mminit_verify_zonelist(void)
 }
 #endif /* CONFIG_DEBUG_MEMORY_INIT */
 
+/*
+ * Deferred struct page initialisation requires init functions that are freed
+ * before kswapd is available. Reuse the memory hotplug section annotation
+ * to mark the required code.
+ *
+ * __defermem_init is code that always exists but is annotated __meminit to
+ *      avoid section warnings.
+ * __defer_init code gets marked __meminit when deferring struct page
+ *      initialistion but is otherwise in the init section.
+ */
+#ifdef CONFIG_DEFERRED_STRUCT_PAGE_INIT
+#define __defermem_init __meminit
+#define __defer_init    __meminit
+#else
+#define __defermem_init
+#define __defer_init __init
+#endif
+
 /* mminit_validate_memmodel_limits is independent of CONFIG_DEBUG_MEMORY_INIT */
 #if defined(CONFIG_SPARSEMEM)
 extern void mminit_validate_memmodel_limits(unsigned long *start_pfn,
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 12a81870815f..7af45b2e8870 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -235,6 +235,64 @@ EXPORT_SYMBOL(nr_online_nodes);
 
 int page_group_by_mobility_disabled __read_mostly;
 
+#ifdef CONFIG_DEFERRED_STRUCT_PAGE_INIT
+static inline void reset_deferred_meminit(pg_data_t *pgdat)
+{
+        pgdat->first_deferred_pfn = ULONG_MAX;
+}
+
+/* Returns true if the struct page for the pfn is uninitialised */
+static inline bool __defermem_init early_page_uninitialised(unsigned long pfn)
+{
+        int nid = early_pfn_to_nid(pfn);
+
+        if (pfn >= NODE_DATA(nid)->first_deferred_pfn)
+                return true;
+
+        return false;
+}
+
+/*
+ * Returns false when the remaining initialisation should be deferred until
+ * later in the boot cycle when it can be parallelised.
+ */
+static inline bool update_defer_init(pg_data_t *pgdat,
+                                unsigned long pfn, unsigned long zone_end,
+                                unsigned long *nr_initialised)
+{
+        /* Always populate low zones for address-contrained allocations */
+        if (zone_end < pgdat_end_pfn(pgdat))
+                return true;
+
+        /* Initialise at least 2G of the highest zone */
+        (*nr_initialised)++;
+        if (*nr_initialised > (2UL << (30 - PAGE_SHIFT)) &&
+            (pfn & (PAGES_PER_SECTION - 1)) == 0) {
+                pgdat->first_deferred_pfn = pfn;
+                return false;
+        }
+
+        return true;
+}
+#else
+static inline void reset_deferred_meminit(pg_data_t *pgdat)
+{
+}
+
+static inline bool early_page_uninitialised(unsigned long pfn)
+{
+        return false;
+}
+
+static inline bool update_defer_init(pg_data_t *pgdat,
+                                unsigned long pfn, unsigned long zone_end,
+                                unsigned long *nr_initialised)
+{
+        return true;
+}
+#endif
+
+
 void set_pageblock_migratetype(struct page *page, int migratetype)
 {
         if (unlikely(page_group_by_mobility_disabled &&
@@ -878,8 +936,8 @@ static void __free_pages_ok(struct page *page, unsigned int order)
         local_irq_restore(flags);
 }
 
-void __init __free_pages_bootmem(struct page *page, unsigned long pfn,
-                                                        unsigned int order)
+static void __defer_init __free_pages_boot_core(struct page *page,
+                                        unsigned long pfn, unsigned int order)
 {
         unsigned int nr_pages = 1 << order;
         struct page *p = page;
@@ -951,6 +1009,14 @@ static inline bool __meminit meminit_pfn_in_nid(unsigned long pfn, int node,
 #endif
 
 
+void __defer_init __free_pages_bootmem(struct page *page, unsigned long pfn,
+                                                        unsigned int order)
+{
+        if (early_page_uninitialised(pfn))
+                return;
+        return __free_pages_boot_core(page, pfn, order);
+}
+
 #ifdef CONFIG_CMA
 /* Free whole pageblock and set its migration type to MIGRATE_CMA. */
 void __init init_cma_reserved_pageblock(struct page *page)
@@ -4325,14 +4391,16 @@ static void setup_zone_migrate_reserve(struct zone *zone)
 void __meminit memmap_init_zone(unsigned long size, int nid, unsigned long zone,
                 unsigned long start_pfn, enum memmap_context context)
 {
+        pg_data_t *pgdat = NODE_DATA(nid);
         unsigned long end_pfn = start_pfn + size;
         unsigned long pfn;
         struct zone *z;
+        unsigned long nr_initialised = 0;
 
         if (highest_memmap_pfn < end_pfn - 1)
                 highest_memmap_pfn = end_pfn - 1;
 
-        z = &NODE_DATA(nid)->node_zones[zone];
+        z = &pgdat->node_zones[zone];
         for (pfn = start_pfn; pfn < end_pfn; pfn++) {
                 /*
                  * There can be holes in boot-time mem_map[]s
@@ -4344,6 +4412,9 @@ void __meminit memmap_init_zone(unsigned long size, int nid, unsigned long zone,
                                 continue;
                         if (!early_pfn_in_nid(pfn, nid))
                                 continue;
+                        if (!update_defer_init(pgdat, pfn, end_pfn,
+                                                &nr_initialised))
+                                break;
                 }
                 __init_single_pfn(pfn, zone, nid);
         }
@@ -5144,6 +5215,7 @@ void __paginginit free_area_init_node(int nid, unsigned long *zones_size,
         /* pg_data_t should be reset to zero when it's allocated */
         WARN_ON(pgdat->nr_zones || pgdat->classzone_idx);
 
+        reset_deferred_meminit(pgdat);
         pgdat->node_id = nid;
         pgdat->node_start_pfn = node_start_pfn;
 #ifdef CONFIG_HAVE_MEMBLOCK_NODE_MAP