[PATCH v2 20/20] mm, hugetlb: remove a hugetlb_instantiation_mutex

[Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>]

Now, we have prepared to have an infrastructure in order to remove a this
awkward mutex which serialize all faulting tasks, so remove it.

Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 0501fe5..f2c3a51 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -2504,9 +2504,7 @@ static int unmap_ref_private(struct mm_struct *mm, struct vm_area_struct *vma,
 
 /*
  * Hugetlb_cow() should be called with page lock of the original hugepage held.
- * Called with hugetlb_instantiation_mutex held and pte_page locked so we
- * cannot race with other handlers or page migration.
- * Keep the pte_same checks anyway to make transition from the mutex easier.
+ * Called with pte_page locked so we cannot race with page migration.
  */
 static int hugetlb_cow(struct mm_struct *mm, struct vm_area_struct *vma,
 			unsigned long address, pte_t *ptep, pte_t pte,
@@ -2844,7 +2842,6 @@ int hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
 	int ret;
 	struct page *page = NULL;
 	struct page *pagecache_page = NULL;
-	static DEFINE_MUTEX(hugetlb_instantiation_mutex);
 	struct hstate *h = hstate_vma(vma);
 
 	address &= huge_page_mask(h);
@@ -2864,17 +2861,9 @@ int hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
 	if (!ptep)
 		return VM_FAULT_OOM;
 
-	/*
-	 * Serialize hugepage allocation and instantiation, so that we don't
-	 * get spurious allocation failures if two CPUs race to instantiate
-	 * the same page in the page cache.
-	 */
-	mutex_lock(&hugetlb_instantiation_mutex);
 	entry = huge_ptep_get(ptep);
-	if (huge_pte_none(entry)) {
-		ret = hugetlb_no_page(mm, vma, address, ptep, flags);
-		goto out_mutex;
-	}
+	if (huge_pte_none(entry))
+		return hugetlb_no_page(mm, vma, address, ptep, flags);
 
 	ret = 0;
 
@@ -2887,10 +2876,8 @@ int hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
 	 * consumed.
 	 */
 	if ((flags & FAULT_FLAG_WRITE) && !huge_pte_write(entry)) {
-		if (vma_needs_reservation(h, vma, address) < 0) {
-			ret = VM_FAULT_OOM;
-			goto out_mutex;
-		}
+		if (vma_needs_reservation(h, vma, address) < 0)
+			return VM_FAULT_OOM;
 
 		if (!(vma->vm_flags & VM_MAYSHARE))
 			pagecache_page = hugetlbfs_pagecache_page(h,
@@ -2939,9 +2926,6 @@ out_page_table_lock:
 		unlock_page(page);
 	put_page(page);
 
-out_mutex:
-	mutex_unlock(&hugetlb_instantiation_mutex);
-
 	return ret;
 }
 
-- 
1.7.9.5

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