mm: introduce new field "managed_pages" to struct zone

Currently a zone's present_pages is calcuated as below, which is
inaccurate and may cause trouble to memory hotplug.

	spanned_pages - absent_pages - memmap_pages - dma_reserve.

During fixing bugs caused by inaccurate zone->present_pages, we found
zone->present_pages has been abused.  The field zone->present_pages may
have different meanings in different contexts:

1) pages existing in a zone.
2) pages managed by the buddy system.

For more discussions about the issue, please refer to:
  http://lkml.org/lkml/2012/11/5/866
  https://patchwork.kernel.org/patch/1346751/

This patchset tries to introduce a new field named "managed_pages" to
struct zone, which counts "pages managed by the buddy system".  And revert
zone->present_pages to count "physical pages existing in a zone", which
also keep in consistence with pgdat->node_present_pages.

We will set an initial value for zone->managed_pages in function
free_area_init_core() and will adjust it later if the initial value is
inaccurate.

For DMA/normal zones, the initial value is set to:

	(spanned_pages - absent_pages - memmap_pages - dma_reserve)

Later zone->managed_pages will be adjusted to the accurate value when the
bootmem allocator frees all free pages to the buddy system in function
free_all_bootmem_node() and free_all_bootmem().

The bootmem allocator doesn't touch highmem pages, so highmem zones'
managed_pages is set to the accurate value "spanned_pages - absent_pages"
in function free_area_init_core() and won't be updated anymore.

This patch also adds a new field "managed_pages" to /proc/zoneinfo
and sysrq showmem.

[akpm@linux-foundation.org: small comment tweaks]
Signed-off-by: Jiang Liu <jiang.liu@huawei.com>
Cc: Wen Congyang <wency@cn.fujitsu.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Maciej Rutecki <maciej.rutecki@gmail.com>
Tested-by: Chris Clayton <chris2553@googlemail.com>
Cc: "Rafael J . Wysocki" <rjw@sisk.pl>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Minchan Kim <minchan@kernel.org>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Jianguo Wu <wujianguo@huawei.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 30 insertions, 14 deletions

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 2bf0d43d646b..0b6a6d04300a 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -735,6 +735,13 @@ static void __free_pages_ok(struct page *page, unsigned int order)
         local_irq_restore(flags);
 }
 
+/*
+ * Read access to zone->managed_pages is safe because it's unsigned long,
+ * but we still need to serialize writers. Currently all callers of
+ * __free_pages_bootmem() except put_page_bootmem() should only be used
+ * at boot time. So for shorter boot time, we shift the burden to
+ * put_page_bootmem() to serialize writers.
+ */
 void __meminit __free_pages_bootmem(struct page *page, unsigned int order)
 {
         unsigned int nr_pages = 1 << order;
@@ -750,6 +757,7 @@ void __meminit __free_pages_bootmem(struct page *page, unsigned int order)
                 set_page_count(p, 0);
         }
 
+        page_zone(page)->managed_pages += 1 << order;
         set_page_refcounted(page);
         __free_pages(page, order);
 }
@@ -2984,6 +2992,7 @@ void show_free_areas(unsigned int filter)
                         " isolated(anon):%lukB"
                         " isolated(file):%lukB"
                         " present:%lukB"
+                        " managed:%lukB"
                         " mlocked:%lukB"
                         " dirty:%lukB"
                         " writeback:%lukB"
@@ -3013,6 +3022,7 @@ void show_free_areas(unsigned int filter)
                         K(zone_page_state(zone, NR_ISOLATED_ANON)),
                         K(zone_page_state(zone, NR_ISOLATED_FILE)),
                         K(zone->present_pages),
+                        K(zone->managed_pages),
                         K(zone_page_state(zone, NR_MLOCK)),
                         K(zone_page_state(zone, NR_FILE_DIRTY)),
                         K(zone_page_state(zone, NR_WRITEBACK)),
@@ -4502,48 +4512,54 @@ static void __paginginit free_area_init_core(struct pglist_data *pgdat,
 
         for (j = 0; j < MAX_NR_ZONES; j++) {
                 struct zone *zone = pgdat->node_zones + j;
-                unsigned long size, realsize, memmap_pages;
+                unsigned long size, realsize, freesize, memmap_pages;
 
                 size = zone_spanned_pages_in_node(nid, j, zones_size);
-                realsize = size - zone_absent_pages_in_node(nid, j,
+                realsize = freesize = size - zone_absent_pages_in_node(nid, j,
                                                                 zholes_size);
 
                 /*
-                 * Adjust realsize so that it accounts for how much memory
+                 * Adjust freesize so that it accounts for how much memory
                  * is used by this zone for memmap. This affects the watermark
                  * and per-cpu initialisations
                  */
                 memmap_pages =
                         PAGE_ALIGN(size * sizeof(struct page)) >> PAGE_SHIFT;
-                if (realsize >= memmap_pages) {
-                        realsize -= memmap_pages;
+                if (freesize >= memmap_pages) {
+                        freesize -= memmap_pages;
                         if (memmap_pages)
                                 printk(KERN_DEBUG
                                        "  %s zone: %lu pages used for memmap\n",
                                        zone_names[j], memmap_pages);
                 } else
                         printk(KERN_WARNING
-                                "  %s zone: %lu pages exceeds realsize %lu\n",
-                                zone_names[j], memmap_pages, realsize);
+                                "  %s zone: %lu pages exceeds freesize %lu\n",
+                                zone_names[j], memmap_pages, freesize);
 
                 /* Account for reserved pages */
-                if (j == 0 && realsize > dma_reserve) {
-                        realsize -= dma_reserve;
+                if (j == 0 && freesize > dma_reserve) {
+                        freesize -= dma_reserve;
                         printk(KERN_DEBUG "  %s zone: %lu pages reserved\n",
                                         zone_names[0], dma_reserve);
                 }
 
                 if (!is_highmem_idx(j))
-                        nr_kernel_pages += realsize;
-                nr_all_pages += realsize;
+                        nr_kernel_pages += freesize;
+                nr_all_pages += freesize;
 
                 zone->spanned_pages = size;
-                zone->present_pages = realsize;
+                zone->present_pages = freesize;
+                /*
+                 * Set an approximate value for lowmem here, it will be adjusted
+                 * when the bootmem allocator frees pages into the buddy system.
+                 * And all highmem pages will be managed by the buddy system.
+                 */
+                zone->managed_pages = is_highmem_idx(j) ? realsize : freesize;
 #ifdef CONFIG_NUMA
                 zone->node = nid;
-                zone->min_unmapped_pages = (realsize*sysctl_min_unmapped_ratio)
+                zone->min_unmapped_pages = (freesize*sysctl_min_unmapped_ratio)
                                                 / 100;
-                zone->min_slab_pages = (realsize * sysctl_min_slab_ratio) / 100;
+                zone->min_slab_pages = (freesize * sysctl_min_slab_ratio) / 100;
 #endif
                 zone->name = zone_names[j];
                 spin_lock_init(&zone->lock);