[PATCH 06/10] mm/madvise: separate huge PMDs from the PTE walk

[Gregory Price]

The PMD callback still owns huge-PMD locking, splitting and reclaim along
with its PTE-table loop. This obscures the transition between the two
paths.

Move huge-PMD lock ownership into a dedicated helper. Return false after a
requested PMD split succeeds so the callback continues at PTE level. Use
the PMD boundary already supplied by walk_pmd_range().

No functional change intended.

Assisted-by: LLM
Signed-off-by: Gregory Price (Meta) <gourry@xxxxxxxxxx>
---
 mm/madvise.c | 85 +++++++++++++++++++++++++++++-----------------------
 1 file changed, 48 insertions(+), 37 deletions(-)

diff --git a/mm/madvise.c b/mm/madvise.c
index 6b518f7f73651..83b27258c9673 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -435,6 +435,52 @@ madvise_lru_huge_pmd_locked(pmd_t *pmd, pmd_t orig_pmd,
 	madvise_lru_folio(folio, private->pageout, folio_list);
 	return NULL;
 }
+
+/* Return false when a requested split requires a PTE walk. */
+static bool madvise_lru_huge_pmd(pmd_t *pmd, unsigned long addr,
+		unsigned long next, struct mm_walk *walk,
+		bool pageout_anon_only)
+{
+	const struct madvise_walk_private *private = walk->private;
+	struct mmu_gather *tlb = private->tlb;
+	bool pageout = private->pageout;
+	LIST_HEAD(folio_list);
+	struct folio *folio = NULL;
+	spinlock_t *ptl;
+	pmd_t orig_pmd;
+
+	tlb_change_page_size(tlb, HPAGE_PMD_SIZE);
+	ptl = pmd_trans_huge_lock(pmd, walk->vma);
+	if (!ptl)
+		return true;
+
+	orig_pmd = *pmd;
+	if (unlikely(!pmd_present(orig_pmd))) {
+		VM_WARN_ON_ONCE(!pmd_is_valid_softleaf(orig_pmd));
+	} else {
+		folio = madvise_lru_huge_pmd_locked(pmd, orig_pmd, addr, next,
+				walk, &folio_list, pageout_anon_only);
+	}
+	spin_unlock(ptl);
+
+	if (folio) {
+		int err = split_folio(folio);
+
+		folio_unlock(folio);
+		folio_put(folio);
+		return err != 0;
+	}
+	if (pageout)
+		reclaim_pages(&folio_list);
+	return true;
+}
+#else
+static bool madvise_lru_huge_pmd(pmd_t *pmd, unsigned long addr,
+		unsigned long next, struct mm_walk *walk,
+		bool pageout_anon_only)
+{
+	return false;
+}
 #endif
 
 static int madvise_lru_pmd_entry(pmd_t *pmd, unsigned long addr,
@@ -458,44 +504,9 @@ static int madvise_lru_pmd_entry(pmd_t *pmd, unsigned long addr,
 	pageout_anon_only = pageout && !vma_is_anonymous(vma) &&
 				       !can_do_file_pageout(vma);
 
-#ifdef CONFIG_TRANSPARENT_HUGEPAGE
-	if (pmd_trans_huge(*pmd)) {
-		pmd_t orig_pmd;
-		unsigned long next = pmd_addr_end(addr, end);
-
-		tlb_change_page_size(tlb, HPAGE_PMD_SIZE);
-		ptl = pmd_trans_huge_lock(pmd, vma);
-		if (!ptl)
-			return 0;
-
-		orig_pmd = *pmd;
-		if (unlikely(!pmd_present(orig_pmd))) {
-			VM_WARN_ON_ONCE(!pmd_is_valid_softleaf(orig_pmd));
-			goto huge_unlock;
-		}
-
-		folio = madvise_lru_huge_pmd_locked(pmd, orig_pmd, addr, next,
-				walk, &folio_list, pageout_anon_only);
-		if (folio) {
-			int err;
-
-			spin_unlock(ptl);
-			err = split_folio(folio);
-			folio_unlock(folio);
-			folio_put(folio);
-			if (!err)
-				goto regular_folio;
-			return 0;
-		}
-huge_unlock:
-		spin_unlock(ptl);
-		if (pageout)
-			reclaim_pages(&folio_list);
+	if (pmd_trans_huge(*pmd) &&
+	    madvise_lru_huge_pmd(pmd, addr, end, walk, pageout_anon_only))
 		return 0;
-	}
-
-regular_folio:
-#endif
 	tlb_change_page_size(tlb, PAGE_SIZE);
 restart:
 	start_pte = pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
-- 
2.53.0-Meta