khugepaged: move up_read(mmap_sem) out of khugepaged_alloc_page()

Both variants of khugepaged_alloc_page() do up_read(&mm->mmap_sem)
first: no point keep it inside the function.

Link: http://lkml.kernel.org/r/1466021202-61880-33-git-send-email-kirill.shutemov@linux.intel.com
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/khugepaged.c

@@ -739,19 +739,10 @@ static bool khugepaged_prealloc_page(struct page **hpage, bool *wait)
 }
 
 static struct page *
-khugepaged_alloc_page(struct page **hpage, gfp_t gfp, struct mm_struct *mm,
-		       unsigned long address, int node)
+khugepaged_alloc_page(struct page **hpage, gfp_t gfp, int node)
 {
 	VM_BUG_ON_PAGE(*hpage, *hpage);
 
-	/*
-	 * Before allocating the hugepage, release the mmap_sem read lock.
-	 * The allocation can take potentially a long time if it involves
-	 * sync compaction, and we do not need to hold the mmap_sem during
-	 * that. We will recheck the vma after taking it again in write mode.
-	 */
-	up_read(&mm->mmap_sem);
-
 	*hpage = __alloc_pages_node(node, gfp, HPAGE_PMD_ORDER);
 	if (unlikely(!*hpage)) {
 		count_vm_event(THP_COLLAPSE_ALLOC_FAILED);
@@ -812,10 +803,8 @@ static bool khugepaged_prealloc_page(struct page **hpage, bool *wait)
 }
 
 static struct page *
-khugepaged_alloc_page(struct page **hpage, gfp_t gfp, struct mm_struct *mm,
-		       unsigned long address, int node)
+khugepaged_alloc_page(struct page **hpage, gfp_t gfp, int node)
 {
-	up_read(&mm->mmap_sem);
 	VM_BUG_ON(!*hpage);
 
 	return  *hpage;
@@ -936,8 +925,14 @@ static void collapse_huge_page(struct mm_struct *mm,
 	/* Only allocate from the target node */
 	gfp = alloc_hugepage_khugepaged_gfpmask() | __GFP_OTHER_NODE | __GFP_THISNODE;
 
-	/* release the mmap_sem read lock. */
-	new_page = khugepaged_alloc_page(hpage, gfp, mm, address, node);
+	/*
+	 * Before allocating the hugepage, release the mmap_sem read lock.
+	 * The allocation can take potentially a long time if it involves
+	 * sync compaction, and we do not need to hold the mmap_sem during
+	 * that. We will recheck the vma after taking it again in write mode.
+	 */
+	up_read(&mm->mmap_sem);
+	new_page = khugepaged_alloc_page(hpage, gfp, node);
 	if (!new_page) {
 		result = SCAN_ALLOC_HUGE_PAGE_FAIL;
 		goto out_nolock;