[PATCH v4 03/13] mm/khugepaged: rename mthp_present_ptes bitmap to eligible_ptes

[Kiryl Shutsemau <kirill@shutemov.name>]

From: "Kiryl Shutsemau (Meta)" <kas@kernel.org>

The name says less than the bit means.  A set bit means not only that the
PTE is present, but also that it passed the other checks: uffd,
lazyfree, anonymity, sharing.  The PTE can be considered a collapse
source.

mthp_collapse() then reads the bitmap starting at the PMD order, so the
bitmap is not specific to mTHP either.

Name it for what a set bit means, and update the comments that named it.

No functional change.

Assisted-by: LLM
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Signed-off-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
---
 mm/khugepaged.c | 32 ++++++++++++++++----------------
 1 file changed, 16 insertions(+), 16 deletions(-)

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 4979a93e3648..081f705cfca2 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -115,8 +115,8 @@ struct collapse_control {
 	/* nodemask for allocation fallback */
 	nodemask_t alloc_nmask;
 
-	/* Each bit represents a single occupied (!none/zero) page. */
-	DECLARE_BITMAP(mthp_present_ptes, MAX_PTRS_PER_PTE);
+	/* Each bit marks a PTE the scan accepted as a collapse source */
+	DECLARE_BITMAP(eligible_ptes, MAX_PTRS_PER_PTE);
 };
 
 /**
@@ -627,7 +627,7 @@ static void collapse_control_init_scan(struct collapse_control *cc)
 {
 	memset(cc->node_load, 0, sizeof(cc->node_load));
 	nodes_clear(cc->alloc_nmask);
-	bitmap_zero(cc->mthp_present_ptes, MAX_PTRS_PER_PTE);
+	bitmap_zero(cc->eligible_ptes, MAX_PTRS_PER_PTE);
 }
 
 static void release_pte_folio(struct folio *folio)
@@ -1482,15 +1482,15 @@ static unsigned int max_order_from_offset(unsigned int offset)
  * mthp_collapse() consumes the bitmap that is generated during
  * collapse_scan_pmd() to determine what regions and mTHP orders fit best.
  *
- * Each bit in cc->mthp_present_ptes represents a single occupied (!none/zero)
- * page. We start at the PMD order and check if it is eligible for collapse;
+ * Each bit in cc->eligible_ptes marks a PTE the scan accepted as a collapse
+ * source. We start at the PMD order and check if it is eligible for collapse;
  * if not, we check the left and right halves of the PTE page table we are
  * examining at a lower order.
  *
- * For each of these, we determine how many PTE entries are occupied in the
- * range of PTE entries we propose to collapse, then we compare this to a
- * threshold number of PTE entries which would need to be occupied for a
- * collapse to be permitted at that order (accounting for max_ptes_none).
+ * For each of these, we count the eligible PTEs in the range we propose to
+ * collapse, then we compare this to the number of eligible PTEs the range
+ * would need for a collapse to be permitted at that order (accounting for
+ * max_ptes_none).
  *
  * If a collapse is permitted, we attempt to collapse the PTE range into a
  * mTHP.
@@ -1499,7 +1499,7 @@ static enum scan_result mthp_collapse(struct mm_struct *mm,
 		unsigned long address, int referenced, int unmapped,
 		struct collapse_control *cc, unsigned long enabled_orders)
 {
-	unsigned int nr_occupied_ptes, nr_ptes, max_ptes_none;
+	unsigned int nr_eligible_ptes, nr_ptes, max_ptes_none;
 	enum scan_result last_result = SCAN_FAIL;
 	int collapsed = 0;
 	bool alloc_failed = false;
@@ -1514,18 +1514,18 @@ static enum scan_result mthp_collapse(struct mm_struct *mm,
 			goto next_order;
 
 		max_ptes_none = collapse_max_ptes_none(cc, NULL, order);
-		nr_occupied_ptes = bitmap_weight_from(cc->mthp_present_ptes, offset,
+		nr_eligible_ptes = bitmap_weight_from(cc->eligible_ptes, offset,
 						      offset + nr_ptes);
 
 		/*
 		 * Swap PTEs accepted during the scan are counted in @unmapped,
-		 * not in the present-PTE bitmap. Account them for the PMD-order
+		 * not in cc->eligible_ptes. Account them for the PMD-order
 		 * candidate.
 		 */
 		if (is_pmd_order(order))
-			nr_occupied_ptes += unmapped;
+			nr_eligible_ptes += unmapped;
 
-		if (nr_occupied_ptes >= nr_ptes - max_ptes_none) {
+		if (nr_eligible_ptes >= nr_ptes - max_ptes_none) {
 			enum scan_result ret;
 
 			collapse_address = address + offset * PAGE_SIZE;
@@ -1731,8 +1731,8 @@ static enum scan_result collapse_scan_pmd(struct mm_struct *mm,
 			}
 		}
 
-		/* Set bit for occupied pages */
-		__set_bit(i, cc->mthp_present_ptes);
+		/* The scan accepted this PTE as a collapse source */
+		__set_bit(i, cc->eligible_ptes);
 		/*
 		 * Record which node the original page is from and save this
 		 * information to cc->node_load[].
-- 
2.54.0