[PATCH v1 06/16] mm/oom_kill: factor out zapping of VMA into zap_vma_for_reaping()

["David Hildenbrand (Arm)" <david@kernel.org>]

Let's factor it out so we can turn unmap_page_range() into a static
function instead, and so oom reaping has a clean interface to call.

Note that hugetlb is not supported, because it would require a bunch of
hugetlb-specific further actions (see zap_page_range_single_batched()).

Signed-off-by: David Hildenbrand (Arm) <david@kernel.org>
---
 mm/internal.h |  5 +----
 mm/memory.c   | 36 ++++++++++++++++++++++++++++++++----
 mm/oom_kill.c | 15 +--------------
 3 files changed, 34 insertions(+), 22 deletions(-)

diff --git a/mm/internal.h b/mm/internal.h
index 39ab37bb0e1d..df9190f7db0e 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -536,13 +536,10 @@ static inline void sync_with_folio_pmd_zap(struct mm_struct *mm, pmd_t *pmdp)
 }
 
 struct zap_details;
-void unmap_page_range(struct mmu_gather *tlb,
-			     struct vm_area_struct *vma,
-			     unsigned long addr, unsigned long end,
-			     struct zap_details *details);
 void zap_page_range_single_batched(struct mmu_gather *tlb,
 		struct vm_area_struct *vma, unsigned long addr,
 		unsigned long size, struct zap_details *details);
+int zap_vma_for_reaping(struct vm_area_struct *vma);
 int folio_unmap_invalidate(struct address_space *mapping, struct folio *folio,
 			   gfp_t gfp);
 
diff --git a/mm/memory.c b/mm/memory.c
index e4154f03feac..621f38ae1425 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2054,10 +2054,9 @@ static inline unsigned long zap_p4d_range(struct mmu_gather *tlb,
 	return addr;
 }
 
-void unmap_page_range(struct mmu_gather *tlb,
-			     struct vm_area_struct *vma,
-			     unsigned long addr, unsigned long end,
-			     struct zap_details *details)
+static void unmap_page_range(struct mmu_gather *tlb, struct vm_area_struct *vma,
+		unsigned long addr, unsigned long end,
+		struct zap_details *details)
 {
 	pgd_t *pgd;
 	unsigned long next;
@@ -2115,6 +2114,35 @@ static void unmap_single_vma(struct mmu_gather *tlb,
 	}
 }
 
+/**
+ * zap_vma_for_reaping - zap all page table entries in the vma without blocking
+ * @vma: The vma to zap.
+ *
+ * Zap all page table entries in the vma without blocking for use by the oom
+ * killer. Hugetlb vmas are not supported.
+ *
+ * Returns: 0 on success, -EBUSY if we would have to block.
+ */
+int zap_vma_for_reaping(struct vm_area_struct *vma)
+{
+	struct mmu_notifier_range range;
+	struct mmu_gather tlb;
+
+	VM_WARN_ON_ONCE(is_vm_hugetlb_page(vma));
+
+	mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma->vm_mm,
+				vma->vm_start, vma->vm_end);
+	tlb_gather_mmu(&tlb, vma->vm_mm);
+	if (mmu_notifier_invalidate_range_start_nonblock(&range)) {
+		tlb_finish_mmu(&tlb);
+		return -EBUSY;
+	}
+	unmap_page_range(&tlb, vma, range.start, range.end, NULL);
+	mmu_notifier_invalidate_range_end(&range);
+	tlb_finish_mmu(&tlb);
+	return 0;
+}
+
 /**
  * unmap_vmas - unmap a range of memory covered by a list of vma's
  * @tlb: address of the caller's struct mmu_gather
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 0ba56fcd10d5..54b7a8fe5136 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -548,21 +548,8 @@ static bool __oom_reap_task_mm(struct mm_struct *mm)
 		 * count elevated without a good reason.
 		 */
 		if (vma_is_anonymous(vma) || !(vma->vm_flags & VM_SHARED)) {
-			struct mmu_notifier_range range;
-			struct mmu_gather tlb;
-
-			mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0,
-						mm, vma->vm_start,
-						vma->vm_end);
-			tlb_gather_mmu(&tlb, mm);
-			if (mmu_notifier_invalidate_range_start_nonblock(&range)) {
-				tlb_finish_mmu(&tlb);
+			if (zap_vma_for_reaping(vma))
 				ret = false;
-				continue;
-			}
-			unmap_page_range(&tlb, vma, range.start, range.end, NULL);
-			mmu_notifier_invalidate_range_end(&range);
-			tlb_finish_mmu(&tlb);
 		}
 	}
 
-- 
2.43.0