[PATCH v2 05/10] mm/madvise: factor huge-PMD folio processing

[Gregory Price (Meta)]

The huge-PMD branch of madvise_lru_pmd_entry() decides inline whether
the PMD maps a folio worth advising: it checks that the PMD is present,
looks up the folio and applies the shared filters, all between taking
the PMD lock and splitting or advising the folio.

Move those checks into madvise_lru_huge_pmd_folio(), which returns NULL
when there is nothing to do, and move the MADV_COLD young-bit clearing
into madvise_cold_pmd().

The split stays in the caller, which owns the PMD lock that must be
dropped before splitting.

No functional change intended.

Suggested-by: Lorenzo Stoakes (ARM) <ljs@xxxxxxxxxx>
Signed-off-by: Gregory Price (Meta) <gourry@xxxxxxxxxx>
---
 mm/madvise.c | 55 +++++++++++++++++++++++++++++++++++-----------------
 1 file changed, 37 insertions(+), 18 deletions(-)

diff --git a/mm/madvise.c b/mm/madvise.c
index 1bb4f9f0e73a..f847dddada8a 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -407,6 +407,37 @@ static int madvise_lru_split_folio(struct folio *folio)
 	return err;
 }
 
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+static void madvise_cold_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
+		pmd_t *pmd, unsigned long addr, pmd_t orig_pmd)
+{
+	if (!pmd_young(orig_pmd))
+		return;
+
+	pmdp_test_and_clear_young(vma, addr, pmd);
+	tlb_remove_pmd_tlb_entry(tlb, pmd, addr);
+}
+
+/* Return the folio mapped by a huge PMD if it should be advised. */
+static struct folio *madvise_lru_huge_pmd_folio(struct vm_area_struct *vma,
+		unsigned long addr, pmd_t orig_pmd, bool pageout_anon_only)
+{
+	struct folio *folio;
+
+	if (unlikely(!pmd_present(orig_pmd))) {
+		VM_WARN_ON_ONCE(!pmd_is_valid_softleaf(orig_pmd));
+		return NULL;
+	}
+
+	folio = vm_normal_folio_pmd(vma, addr, orig_pmd);
+	if (!folio || folio_is_zone_device(folio))
+		return NULL;
+	if (madvise_lru_folio_is_filtered(folio, pageout_anon_only))
+		return NULL;
+	return folio;
+}
+#endif
+
 static int madvise_lru_pmd_entry(pmd_t *pmd, unsigned long addr,
 		unsigned long end, struct mm_walk *walk)
 {
@@ -432,6 +463,7 @@ static int madvise_lru_pmd_entry(pmd_t *pmd, unsigned long addr,
 	if (pmd_trans_huge(*pmd)) {
 		pmd_t orig_pmd;
 		unsigned long next = pmd_addr_end(addr, end);
+		const bool spans_pmd = next - addr == HPAGE_PMD_SIZE;
 
 		tlb_change_page_size(tlb, HPAGE_PMD_SIZE);
 		ptl = pmd_trans_huge_lock(pmd, vma);
@@ -439,22 +471,12 @@ static int madvise_lru_pmd_entry(pmd_t *pmd, unsigned long addr,
 			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 = vm_normal_folio_pmd(vma, addr, orig_pmd);
+		folio = madvise_lru_huge_pmd_folio(vma, addr, orig_pmd,
+				pageout_anon_only);
 		if (!folio)
 			goto huge_unlock;
 
-		if (folio_is_zone_device(folio))
-			goto huge_unlock;
-
-		if (madvise_lru_folio_is_filtered(folio, pageout_anon_only))
-			goto huge_unlock;
-
-		if (next - addr != HPAGE_PMD_SIZE) {
+		if (!spans_pmd) {
 			if (!folio_trylock(folio))
 				goto huge_unlock;
 			folio_get(folio);
@@ -464,11 +486,8 @@ static int madvise_lru_pmd_entry(pmd_t *pmd, unsigned long addr,
 			return 0;
 		}
 
-		if (!pageout && pmd_young(orig_pmd)) {
-			pmdp_test_and_clear_young(vma, addr, pmd);
-			tlb_remove_pmd_tlb_entry(tlb, pmd, addr);
-		}
-
+		if (!pageout)
+			madvise_cold_pmd(tlb, vma, pmd, addr, orig_pmd);
 		madvise_lru_folio(folio, pageout, &folio_list);
 huge_unlock:
 		spin_unlock(ptl);
-- 
2.56.0