mm: remove managed_page_count_lock spinlock

Now that totalram_pages and managed_pages are atomic varibles, no need of
managed_page_count spinlock.  The lock had really a weak consistency
guarantee.  It hasn't been used for anything but the update but no reader
actually cares about all the values being updated to be in sync.

Link: http://lkml.kernel.org/r/1542090790-21750-5-git-send-email-arunks@codeaurora.org
Signed-off-by: Arun KS <arunks@codeaurora.org>
Reviewed-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: David Hildenbrand <david@redhat.com>
Reviewed-by: Pavel Tatashin <pasha.tatashin@soleen.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/mmzone.h

@@ -428,12 +428,6 @@ struct zone {
 	 * Write access to present_pages at runtime should be protected by
 	 * mem_hotplug_begin/end(). Any reader who can't tolerant drift of
 	 * present_pages should get_online_mems() 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.
 	 */
 	atomic_long_t		managed_pages;
 	unsigned long		spanned_pages;

mm/page_alloc.c

@@ -122,9 +122,6 @@ 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);
-
 atomic_long_t _totalram_pages __read_mostly;
 EXPORT_SYMBOL(_totalram_pages);
 unsigned long totalreserve_pages __read_mostly;
@@ -7077,14 +7074,12 @@ early_param("movablecore", cmdline_parse_movablecore);
 
 void adjust_managed_page_count(struct page *page, long count)
 {
-	spin_lock(&managed_page_count_lock);
 	atomic_long_add(count, &page_zone(page)->managed_pages);
 	totalram_pages_add(count);
 #ifdef CONFIG_HIGHMEM
 	if (PageHighMem(page))
 		totalhigh_pages_add(count);
 #endif
-	spin_unlock(&managed_page_count_lock);
 }
 EXPORT_SYMBOL(adjust_managed_page_count);