[RFC v2 1/9] introduce khugepaged_collapse_single_pmd to unify khugepaged and madvise_collapse

[Nico Pache <npache@redhat.com>]

The khugepaged daemon and madvise_collapse have two different
implementations that do almost the same thing.

Create khugepaged_collapse_single_pmd to increase code
reuse and create an entry point for future khugepaged changes.

Refactor madvise_collapse and khugepaged_scan_mm_slot to use
the new khugepaged_collapse_single_pmd function.

Signed-off-by: Nico Pache <npache@redhat.com>
---
 mm/khugepaged.c | 96 +++++++++++++++++++++++++------------------------
 1 file changed, 50 insertions(+), 46 deletions(-)

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 5f0be134141e..46faee67378b 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -2365,6 +2365,52 @@ static int hpage_collapse_scan_file(struct mm_struct *mm, unsigned long addr,
 }
 #endif
 
+/*
+ * Try to collapse a single PMD starting at a PMD aligned addr, and return
+ * the results.
+ */
+static int khugepaged_collapse_single_pmd(unsigned long addr, struct mm_struct *mm,
+				   struct vm_area_struct *vma, bool *mmap_locked,
+				   struct collapse_control *cc)
+{
+	int result = SCAN_FAIL;
+	unsigned long tva_flags = cc->is_khugepaged ? TVA_ENFORCE_SYSFS : 0;
+
+	if (!*mmap_locked) {
+		mmap_read_lock(mm);
+		*mmap_locked = true;
+	}
+
+	if (thp_vma_allowable_order(vma, vma->vm_flags,
+					tva_flags, PMD_ORDER)) {
+		if (IS_ENABLED(CONFIG_SHMEM) && !vma_is_anonymous(vma)) {
+			struct file *file = get_file(vma->vm_file);
+			pgoff_t pgoff = linear_page_index(vma, addr);
+
+			mmap_read_unlock(mm);
+			*mmap_locked = false;
+			result = hpage_collapse_scan_file(mm, addr, file, pgoff,
+							  cc);
+			fput(file);
+			if (result == SCAN_PTE_MAPPED_HUGEPAGE) {
+				mmap_read_lock(mm);
+				if (hpage_collapse_test_exit_or_disable(mm))
+					goto end;
+				result = collapse_pte_mapped_thp(mm, addr,
+								 !cc->is_khugepaged);
+				mmap_read_unlock(mm);
+			}
+		} else {
+			result = hpage_collapse_scan_pmd(mm, vma, addr,
+							 mmap_locked, cc);
+		}
+		if (result == SCAN_SUCCEED || result == SCAN_PMD_MAPPED)
+			++khugepaged_pages_collapsed;
+	}
+end:
+	return result;
+}
+
 static unsigned int khugepaged_scan_mm_slot(unsigned int pages, int *result,
 					    struct collapse_control *cc)
 	__releases(&khugepaged_mm_lock)
@@ -2439,33 +2485,9 @@ static unsigned int khugepaged_scan_mm_slot(unsigned int pages, int *result,
 			VM_BUG_ON(khugepaged_scan.address < hstart ||
 				  khugepaged_scan.address + HPAGE_PMD_SIZE >
 				  hend);
-			if (IS_ENABLED(CONFIG_SHMEM) && !vma_is_anonymous(vma)) {
-				struct file *file = get_file(vma->vm_file);
-				pgoff_t pgoff = linear_page_index(vma,
-						khugepaged_scan.address);
 
-				mmap_read_unlock(mm);
-				mmap_locked = false;
-				*result = hpage_collapse_scan_file(mm,
-					khugepaged_scan.address, file, pgoff, cc);
-				fput(file);
-				if (*result == SCAN_PTE_MAPPED_HUGEPAGE) {
-					mmap_read_lock(mm);
-					if (hpage_collapse_test_exit_or_disable(mm))
-						goto breakouterloop;
-					*result = collapse_pte_mapped_thp(mm,
-						khugepaged_scan.address, false);
-					if (*result == SCAN_PMD_MAPPED)
-						*result = SCAN_SUCCEED;
-					mmap_read_unlock(mm);
-				}
-			} else {
-				*result = hpage_collapse_scan_pmd(mm, vma,
-					khugepaged_scan.address, &mmap_locked, cc);
-			}
-
-			if (*result == SCAN_SUCCEED)
-				++khugepaged_pages_collapsed;
+			*result = khugepaged_collapse_single_pmd(khugepaged_scan.address,
+						mm, vma, &mmap_locked, cc);
 
 			/* move to next address */
 			khugepaged_scan.address += HPAGE_PMD_SIZE;
@@ -2785,36 +2807,18 @@ int madvise_collapse(struct vm_area_struct *vma, struct vm_area_struct **prev,
 		mmap_assert_locked(mm);
 		memset(cc->node_load, 0, sizeof(cc->node_load));
 		nodes_clear(cc->alloc_nmask);
-		if (IS_ENABLED(CONFIG_SHMEM) && !vma_is_anonymous(vma)) {
-			struct file *file = get_file(vma->vm_file);
-			pgoff_t pgoff = linear_page_index(vma, addr);
 
-			mmap_read_unlock(mm);
-			mmap_locked = false;
-			result = hpage_collapse_scan_file(mm, addr, file, pgoff,
-							  cc);
-			fput(file);
-		} else {
-			result = hpage_collapse_scan_pmd(mm, vma, addr,
-							 &mmap_locked, cc);
-		}
+		result = khugepaged_collapse_single_pmd(addr, mm, vma, &mmap_locked, cc);
+
 		if (!mmap_locked)
 			*prev = NULL;  /* Tell caller we dropped mmap_lock */
 
-handle_result:
 		switch (result) {
 		case SCAN_SUCCEED:
 		case SCAN_PMD_MAPPED:
 			++thps;
 			break;
 		case SCAN_PTE_MAPPED_HUGEPAGE:
-			BUG_ON(mmap_locked);
-			BUG_ON(*prev);
-			mmap_read_lock(mm);
-			result = collapse_pte_mapped_thp(mm, addr, true);
-			mmap_read_unlock(mm);
-			goto handle_result;
-		/* Whitelisted set of results where continuing OK */
 		case SCAN_PMD_NULL:
 		case SCAN_PTE_NON_PRESENT:
 		case SCAN_PTE_UFFD_WP:
-- 
2.48.1