[PATCH 3/3] CMA: Add cma_alloc_counter to make cma_alloc work better if it meet busy range

[Hui Zhu <zhuhui@xiaomi.com>]

In [1], Joonsoo said that cma_alloc_counter is useless because pageblock
is isolated.
But if alloc_contig_range meet a busy range, it will undo_isolate_page_range
before goto try next range. At this time, __rmqueue_cma can begin allocd
CMA memory from the range.

So I add cma_alloc_counter let __rmqueue doesn't call __rmqueue_cma when
cma_alloc works.

[1] https://lkml.org/lkml/2014/10/24/26

Signed-off-by: Hui Zhu <zhuhui@xiaomi.com>
---
 include/linux/cma.h | 2 ++
 mm/cma.c            | 6 ++++++
 mm/page_alloc.c     | 8 +++++++-
 3 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/include/linux/cma.h b/include/linux/cma.h
index 9384ba6..155158f 100644
--- a/include/linux/cma.h
+++ b/include/linux/cma.h
@@ -26,6 +26,8 @@ extern int __init cma_declare_contiguous(phys_addr_t base,
 extern int cma_init_reserved_mem(phys_addr_t base,
 					phys_addr_t size, int order_per_bit,
 					struct cma **res_cma);
+
+extern atomic_t cma_alloc_counter;
 extern struct page *cma_alloc(struct cma *cma, int count, unsigned int align);
 extern bool cma_release(struct cma *cma, struct page *pages, int count);
 #endif
diff --git a/mm/cma.c b/mm/cma.c
index 6707b5d..b63f6be 100644
--- a/mm/cma.c
+++ b/mm/cma.c
@@ -348,6 +348,8 @@ err:
 	return ret;
 }
 
+atomic_t cma_alloc_counter = ATOMIC_INIT(0);
+
 /**
  * cma_alloc() - allocate pages from contiguous area
  * @cma:   Contiguous memory region for which the allocation is performed.
@@ -378,6 +380,8 @@ struct page *cma_alloc(struct cma *cma, int count, unsigned int align)
 	bitmap_maxno = cma_bitmap_maxno(cma);
 	bitmap_count = cma_bitmap_pages_to_bits(cma, count);
 
+	atomic_inc(&cma_alloc_counter);
+
 	for (;;) {
 		mutex_lock(&cma->lock);
 		bitmap_no = bitmap_find_next_zero_area_off(cma->bitmap,
@@ -415,6 +419,8 @@ struct page *cma_alloc(struct cma *cma, int count, unsigned int align)
 		start = bitmap_no + mask + 1;
 	}
 
+	atomic_dec(&cma_alloc_counter);
+
 	pr_debug("%s(): returned %p\n", __func__, page);
 	return page;
 }
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index a5bbc38..0622c4c 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -66,6 +66,10 @@
 #include <asm/div64.h>
 #include "internal.h"
 
+#ifdef CONFIG_CMA
+#include <linux/cma.h>
+#endif
+
 /* prevent >1 _updater_ of zone percpu pageset ->high and ->batch fields */
 static DEFINE_MUTEX(pcp_batch_high_lock);
 #define MIN_PERCPU_PAGELIST_FRACTION	(8)
@@ -1330,7 +1334,9 @@ static struct page *__rmqueue(struct zone *zone, unsigned int order,
 {
 	struct page *page = NULL;
 
-	if (IS_ENABLED(CONFIG_CMA) && zone->managed_cma_pages) {
+	if (IS_ENABLED(CONFIG_CMA)
+	    && zone->managed_cma_pages
+	    && atomic_read(&cma_alloc_counter) == 0) {
 		if (migratetype == MIGRATE_MOVABLE
 		    && zone->nr_try_movable <= 0)
 			page = __rmqueue_cma(zone, order);
-- 
1.9.1