mm: use a dedicated lock to protect totalram_pages and zone->managed_…

…pages

Currently lock_memory_hotplug()/unlock_memory_hotplug() are used to
protect totalram_pages and zone->managed_pages.  Other than the memory
hotplug driver, totalram_pages and zone->managed_pages may also be
modified at runtime by other drivers, such as Xen balloon,
virtio_balloon etc.  For those cases, memory hotplug lock is a little
too heavy, so introduce a dedicated lock to protect totalram_pages and
zone->managed_pages.

Now we have a simplified locking rules totalram_pages and
zone->managed_pages as:

1) no locking for read accesses because they are unsigned long.
2) no locking for write accesses at boot time in single-threaded context.
3) serialize write accesses at runtime by acquiring the dedicated
   managed_page_count_lock.

Also adjust zone->managed_pages when freeing reserved pages into the
buddy system, to keep totalram_pages and zone->managed_pages in
consistence.

[[email protected]: don't export adjust_managed_page_count to modules (for now)]
Signed-off-by: Jiang Liu <[email protected]>
Cc: Mel Gorman <[email protected]>
Cc: Michel Lespinasse <[email protected]>
Cc: Rik van Riel <[email protected]>
Cc: Minchan Kim <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Cc: "Michael S. Tsirkin" <[email protected]>
Cc: <[email protected]>
Cc: Arnd Bergmann <[email protected]>
Cc: Catalin Marinas <[email protected]>
Cc: Chris Metcalf <[email protected]>
Cc: David Howells <[email protected]>
Cc: Geert Uytterhoeven <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Jeremy Fitzhardinge <[email protected]>
Cc: Jianguo Wu <[email protected]>
Cc: Joonsoo Kim <[email protected]>
Cc: Kamezawa Hiroyuki <[email protected]>
Cc: Konrad Rzeszutek Wilk <[email protected]>
Cc: Marek Szyprowski <[email protected]>
Cc: Rusty Russell <[email protected]>
Cc: Tang Chen <[email protected]>
Cc: Tejun Heo <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Wen Congyang <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: Yasuaki Ishimatsu <[email protected]>
Cc: Yinghai Lu <[email protected]>
Cc: Russell King <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

include/linux/mm.h

@@ -1313,6 +1313,7 @@ extern void free_initmem(void);
  */
 extern unsigned long free_reserved_area(void *start, void *end,
 					int poison, char *s);
+
 #ifdef	CONFIG_HIGHMEM
 /*
  * Free a highmem page into the buddy system, adjusting totalhigh_pages
@@ -1321,10 +1322,7 @@ extern unsigned long free_reserved_area(void *start, void *end,
 extern void free_highmem_page(struct page *page);
 #endif
 
-static inline void adjust_managed_page_count(struct page *page, long count)
-{
-	totalram_pages += count;
-}
+extern void adjust_managed_page_count(struct page *page, long count);
 
 /* Free the reserved page into the buddy system, so it gets managed. */
 static inline void __free_reserved_page(struct page *page)

include/linux/mmzone.h

@@ -474,10 +474,16 @@ struct zone {
 	 * frequently read in proximity to zone->lock.  It's good to
 	 * give them a chance of being in the same cacheline.
 	 *
-	 * Write access to present_pages and managed_pages at runtime should
-	 * be protected by lock_memory_hotplug()/unlock_memory_hotplug().
-	 * Any reader who can't tolerant drift of present_pages and
-	 * managed_pages should hold memory hotplug lock to get a stable value.
+	 * Write access to present_pages at runtime should be protected by
+	 * lock_memory_hotplug()/unlock_memory_hotplug().  Any reader who can't
+	 * tolerant drift of present_pages should hold memory hotplug lock to
+	 * get a stable value.
+	 *
+	 * Read access to managed_pages should be safe because it's unsigned
+	 * long. Write access to zone->managed_pages and totalram_pages are
+	 * protected by managed_page_count_lock at runtime. Idealy only
+	 * adjust_managed_page_count() should be used instead of directly
+	 * touching zone->managed_pages and totalram_pages.
 	 */
 	unsigned long		spanned_pages;
 	unsigned long		present_pages;

mm/page_alloc.c

@@ -103,6 +103,9 @@ nodemask_t node_states[NR_NODE_STATES] __read_mostly = {
 };
 EXPORT_SYMBOL(node_states);
 
+/* Protect totalram_pages and zone->managed_pages */
+static DEFINE_SPINLOCK(managed_page_count_lock);
+
 unsigned long totalram_pages __read_mostly;
 unsigned long totalreserve_pages __read_mostly;
 /*
@@ -5206,6 +5209,14 @@ early_param("movablecore", cmdline_parse_movablecore);
 
 #endif /* CONFIG_HAVE_MEMBLOCK_NODE_MAP */
 
+void adjust_managed_page_count(struct page *page, long count)
+{
+	spin_lock(&managed_page_count_lock);
+	page_zone(page)->managed_pages += count;
+	totalram_pages += count;
+	spin_unlock(&managed_page_count_lock);
+}
+
 unsigned long free_reserved_area(void *start, void *end, int poison, char *s)
 {
 	void *pos;