[PATCH] mm: Refactor vma_map_pages to use vm_insert_pages

[Justin Green <greenjustin@chromium.org>]

vma_map_pages currently calls vm_insert_page on each individual page in
the mapping, which creates significant overhead because we are
repeatedly spinlocking. Instead, we should batch insert pages using
vm_insert_pages, which amortizes the cost of the spinlock.

Tested through watching hardware accelerated video on a MTK ChromeOS
device. This particular path maps both a V4L2 buffer and a GEM allocated
buffer into userspace and converts the contents from one pixel format to
another. Both vb2_mmap() and mtk_gem_object_mmap() exercise this
pathway.

Signed-off-by: Justin Green <greenjustin@chromium.org>
---
 mm/memory.c | 10 +---------
 1 file changed, 1 insertion(+), 9 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index da360a6eb8a4..7ae6ac42e7d8 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2499,7 +2499,6 @@ static int __vm_map_pages(struct vm_area_struct *vma, struct page **pages,
 {
 	unsigned long count = vma_pages(vma);
 	unsigned long uaddr = vma->vm_start;
-	int ret, i;
 
 	/* Fail if the user requested offset is beyond the end of the object */
 	if (offset >= num)
@@ -2509,14 +2508,7 @@ static int __vm_map_pages(struct vm_area_struct *vma, struct page **pages,
 	if (count > num - offset)
 		return -ENXIO;
 
-	for (i = 0; i < count; i++) {
-		ret = vm_insert_page(vma, uaddr, pages[offset + i]);
-		if (ret < 0)
-			return ret;
-		uaddr += PAGE_SIZE;
-	}
-
-	return 0;
+	return vm_insert_pages(vma, uaddr, pages + offset, &count);
 }
 
 /**
-- 
2.53.0.rc1.217.geba53bf80e-goog