[v3 PATCH 5/8] mm: khugepaged: make khugepaged_enter() void function

[Yang Shi]

The most callers of khugepaged_enter() don't care about the return
value.  Only dup_mmap(), anonymous THP page fault and MADV_HUGEPAGE handle
the error by returning -ENOMEM.  Actually it is not harmful for them to
ignore the error case either.  It also sounds overkilling to fail fork()
and page fault early due to khugepaged_enter() error, and MADV_HUGEPAGE
does set VM_HUGEPAGE flag regardless of the error.

Acked-by: Song Liu <song@xxxxxxxxxx>
Signed-off-by: Yang Shi <shy828301@xxxxxxxxx>
---
 include/linux/khugepaged.h | 30 ++++++++++++------------------
 kernel/fork.c              |  4 +---
 mm/huge_memory.c           |  4 ++--
 mm/khugepaged.c            | 18 +++++++-----------
 4 files changed, 22 insertions(+), 34 deletions(-)

diff --git a/include/linux/khugepaged.h b/include/linux/khugepaged.h
index 2fcc01891b47..0423d3619f26 100644
--- a/include/linux/khugepaged.h
+++ b/include/linux/khugepaged.h
@@ -12,10 +12,10 @@ extern struct attribute_group khugepaged_attr_group;
 extern int khugepaged_init(void);
 extern void khugepaged_destroy(void);
 extern int start_stop_khugepaged(void);
-extern int __khugepaged_enter(struct mm_struct *mm);
+extern void __khugepaged_enter(struct mm_struct *mm);
 extern void __khugepaged_exit(struct mm_struct *mm);
-extern int khugepaged_enter_vma_merge(struct vm_area_struct *vma,
-				      unsigned long vm_flags);
+extern void khugepaged_enter_vma_merge(struct vm_area_struct *vma,
+				       unsigned long vm_flags);
 extern void khugepaged_min_free_kbytes_update(void);
 #ifdef CONFIG_SHMEM
 extern void collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr);
@@ -40,11 +40,10 @@ static inline void collapse_pte_mapped_thp(struct mm_struct *mm,
 	(transparent_hugepage_flags &				\
 	 (1<<TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG))
 
-static inline int khugepaged_fork(struct mm_struct *mm, struct mm_struct *oldmm)
+static inline void khugepaged_fork(struct mm_struct *mm, struct mm_struct *oldmm)
 {
 	if (test_bit(MMF_VM_HUGEPAGE, &oldmm->flags))
-		return __khugepaged_enter(mm);
-	return 0;
+		__khugepaged_enter(mm);
 }
 
 static inline void khugepaged_exit(struct mm_struct *mm)
@@ -53,7 +52,7 @@ static inline void khugepaged_exit(struct mm_struct *mm)
 		__khugepaged_exit(mm);
 }
 
-static inline int khugepaged_enter(struct vm_area_struct *vma,
+static inline void khugepaged_enter(struct vm_area_struct *vma,
 				   unsigned long vm_flags)
 {
 	if (!test_bit(MMF_VM_HUGEPAGE, &vma->vm_mm->flags))
@@ -62,27 +61,22 @@ static inline int khugepaged_enter(struct vm_area_struct *vma,
 		     (khugepaged_req_madv() && (vm_flags & VM_HUGEPAGE))) &&
 		    !(vm_flags & VM_NOHUGEPAGE) &&
 		    !test_bit(MMF_DISABLE_THP, &vma->vm_mm->flags))
-			if (__khugepaged_enter(vma->vm_mm))
-				return -ENOMEM;
-	return 0;
+			__khugepaged_enter(vma->vm_mm);
 }
 #else /* CONFIG_TRANSPARENT_HUGEPAGE */
-static inline int khugepaged_fork(struct mm_struct *mm, struct mm_struct *oldmm)
+static inline void khugepaged_fork(struct mm_struct *mm, struct mm_struct *oldmm)
 {
-	return 0;
 }
 static inline void khugepaged_exit(struct mm_struct *mm)
 {
 }
-static inline int khugepaged_enter(struct vm_area_struct *vma,
-				   unsigned long vm_flags)
+static inline void khugepaged_enter(struct vm_area_struct *vma,
+				    unsigned long vm_flags)
 {
-	return 0;
 }
-static inline int khugepaged_enter_vma_merge(struct vm_area_struct *vma,
-					     unsigned long vm_flags)
+static inline void khugepaged_enter_vma_merge(struct vm_area_struct *vma,
+					      unsigned long vm_flags)
 {
-	return 0;
 }
 static inline void collapse_pte_mapped_thp(struct mm_struct *mm,
 					   unsigned long addr)
diff --git a/kernel/fork.c b/kernel/fork.c
index 9796897560ab..0d13baf86650 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -612,9 +612,7 @@ static __latent_entropy int dup_mmap(struct mm_struct *mm,
 	retval = ksm_fork(mm, oldmm);
 	if (retval)
 		goto out;
-	retval = khugepaged_fork(mm, oldmm);
-	if (retval)
-		goto out;
+	khugepaged_fork(mm, oldmm);
 
 	prev = NULL;
 	for (mpnt = oldmm->mmap; mpnt; mpnt = mpnt->vm_next) {
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 183b793fd28e..4fd5a6a79d44 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -725,8 +725,8 @@ vm_fault_t do_huge_pmd_anonymous_page(struct vm_fault *vmf)
 		return VM_FAULT_FALLBACK;
 	if (unlikely(anon_vma_prepare(vma)))
 		return VM_FAULT_OOM;
-	if (unlikely(khugepaged_enter(vma, vma->vm_flags)))
-		return VM_FAULT_OOM;
+	khugepaged_enter(vma, vma->vm_flags);
+
 	if (!(vmf->flags & FAULT_FLAG_WRITE) &&
 			!mm_forbids_zeropage(vma->vm_mm) &&
 			transparent_hugepage_use_zero_page()) {
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 609c1bc0a027..b69eda934d70 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -365,8 +365,7 @@ int hugepage_madvise(struct vm_area_struct *vma,
 		 * register it here without waiting a page fault that
 		 * may not happen any time soon.
 		 */
-		if (khugepaged_enter_vma_merge(vma, *vm_flags))
-			return -ENOMEM;
+		khugepaged_enter_vma_merge(vma, *vm_flags);
 		break;
 	case MADV_NOHUGEPAGE:
 		*vm_flags &= ~VM_HUGEPAGE;
@@ -475,20 +474,20 @@ static bool hugepage_vma_check(struct vm_area_struct *vma,
 	return true;
 }
 
-int __khugepaged_enter(struct mm_struct *mm)
+void __khugepaged_enter(struct mm_struct *mm)
 {
 	struct mm_slot *mm_slot;
 	int wakeup;
 
 	mm_slot = alloc_mm_slot();
 	if (!mm_slot)
-		return -ENOMEM;
+		return;
 
 	/* __khugepaged_exit() must not run from under us */
 	VM_BUG_ON_MM(khugepaged_test_exit(mm), mm);
 	if (unlikely(test_and_set_bit(MMF_VM_HUGEPAGE, &mm->flags))) {
 		free_mm_slot(mm_slot);
-		return 0;
+		return;
 	}
 
 	spin_lock(&khugepaged_mm_lock);
@@ -504,11 +503,9 @@ int __khugepaged_enter(struct mm_struct *mm)
 	mmgrab(mm);
 	if (wakeup)
 		wake_up_interruptible(&khugepaged_wait);
-
-	return 0;
 }
 
-int khugepaged_enter_vma_merge(struct vm_area_struct *vma,
+void khugepaged_enter_vma_merge(struct vm_area_struct *vma,
 			       unsigned long vm_flags)
 {
 	unsigned long hstart, hend;
@@ -519,13 +516,12 @@ int khugepaged_enter_vma_merge(struct vm_area_struct *vma,
 	 * file-private shmem THP is not supported.
 	 */
 	if (!hugepage_vma_check(vma, vm_flags))
-		return 0;
+		return;
 
 	hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
 	hend = vma->vm_end & HPAGE_PMD_MASK;
 	if (hstart < hend)
-		return khugepaged_enter(vma, vm_flags);
-	return 0;
+		khugepaged_enter(vma, vm_flags);
 }
 
 void __khugepaged_exit(struct mm_struct *mm)
-- 
2.26.3