Changelog:
  - change the logic from "do charge after unlock" to
    "do charge before lock".
---
 mm/memory.c |   56 ++++++++++++++++++++++++++++++++++----------------------
 1 files changed, 34 insertions(+), 22 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index 87d9353..845378c 100644
--- a/mm/memory.c
+++ b/mm/memory.c

@@ -3127,14 +3127,34 @@ static int __do_fault(struct mm_struct *mm, struct vm_area_struct *vma,
 	pte_t *page_table;
 	spinlock_t *ptl;
 	struct page *page;
+	struct page *cow_page;
 	pte_t entry;
 	int anon = 0;
-	int charged = 0;
 	struct page *dirty_page = NULL;
 	struct vm_fault vmf;
 	int ret;
 	int page_mkwrite = 0;
 
+	/*
+	 * If we do COW later, allocate page befor taking lock_page()
+	 * on the file cache page. This will reduce lock holding time.
+	 */
+	if ((flags & FAULT_FLAG_WRITE) && !(vma->vm_flags & VM_SHARED)) {
+
+		if (unlikely(anon_vma_prepare(vma)))
+			return  VM_FAULT_OOM;
+
+		cow_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, address);
+		if (!cow_page)
+			return VM_FAULT_OOM;
+
+		if (mem_cgroup_newpage_charge(cow_page, mm, GFP_KERNEL)) {
+			page_cache_release(cow_page);
+			return VM_FAULT_OOM;
+		}
+	} else
+		cow_page = NULL;
+
 	vmf.virtual_address = (void __user *)(address & PAGE_MASK);
 	vmf.pgoff = pgoff;
 	vmf.flags = flags;

@@ -3143,12 +3163,13 @@ static int __do_fault(struct mm_struct *mm, struct vm_area_struct *vma,
 	ret = vma->vm_ops->fault(vma, &vmf);
 	if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE |
 			    VM_FAULT_RETRY)))
-		return ret;
+		goto uncharge_out;
 
 	if (unlikely(PageHWPoison(vmf.page))) {
 		if (ret & VM_FAULT_LOCKED)
 			unlock_page(vmf.page);
-		return VM_FAULT_HWPOISON;
+		ret = VM_FAULT_HWPOISON;
+		goto uncharge_out;
 	}
 
 	/*

@@ -3166,23 +3187,8 @@ static int __do_fault(struct mm_struct *mm, struct vm_area_struct *vma,
 	page = vmf.page;
 	if (flags & FAULT_FLAG_WRITE) {
 		if (!(vma->vm_flags & VM_SHARED)) {
+			page = cow_page;
 			anon = 1;
-			if (unlikely(anon_vma_prepare(vma))) {
-				ret = VM_FAULT_OOM;
-				goto out;
-			}
-			page = alloc_page_vma(GFP_HIGHUSER_MOVABLE,
-						vma, address);
-			if (!page) {
-				ret = VM_FAULT_OOM;
-				goto out;
-			}
-			if (mem_cgroup_newpage_charge(page, mm, GFP_KERNEL)) {
-				ret = VM_FAULT_OOM;
-				page_cache_release(page);
-				goto out;
-			}
-			charged = 1;
 			copy_user_highpage(page, vmf.page, address, vma);
 			__SetPageUptodate(page);
 		} else {

@@ -3251,8 +3257,8 @@ static int __do_fault(struct mm_struct *mm, struct vm_area_struct *vma,
 		/* no need to invalidate: a not-present page won't be cached */
 		update_mmu_cache(vma, address, page_table);
 	} else {
-		if (charged)
-			mem_cgroup_uncharge_page(page);
+		if (cow_page)
+			mem_cgroup_uncharge_page(cow_page);
 		if (anon)
 			page_cache_release(page);
 		else

@@ -3261,7 +3267,6 @@ static int __do_fault(struct mm_struct *mm, struct vm_area_struct *vma,
 
 	pte_unmap_unlock(page_table, ptl);
 
-out:
 	if (dirty_page) {
 		struct address_space *mapping = page->mapping;
 

@@ -3291,6 +3296,13 @@ out:
 unwritable_page:
 	page_cache_release(page);
 	return ret;
+uncharge_out:
+	/* fs's fault handler get error */
+	if (cow_page) {
+		mem_cgroup_uncharge_page(cow_page);
+		page_cache_release(cow_page);
+	}
+	return ret;
 }
 
 static int do_linear_fault(struct mm_struct *mm, struct vm_area_struct *vma,

-- 
1.7.4.1



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