This patch extends DAMOS_STAT handling of the DAMON operations
sets for virtual address spaces for ops-level DAMOS filters.
It leverages the walk_page_range to walk the page table and gets
the folio from page table. The last folio scanned is stored in
damos->last_applied to prevent double counting.

Signed-off-by: Yueyang Pan <pyyjason@gmail.com>
---
 mm/damon/vaddr.c | 103 ++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 102 insertions(+), 1 deletion(-)

diff --git a/mm/damon/vaddr.c b/mm/damon/vaddr.c
index 87e825349bdf..66ef9869eafe 100644
--- a/mm/damon/vaddr.c
+++ b/mm/damon/vaddr.c
@@ -890,6 +890,107 @@ static unsigned long damos_va_migrate(struct damon_target *target,
 	return applied * PAGE_SIZE;
 }
 
+struct damos_va_stat_private {
+	struct damos *scheme;
+	unsigned long *sz_filter_passed;
+};
+
+static inline bool damos_va_invalid_folio(struct folio *folio,
+		struct damos *s)
+{
+	return !folio || folio == s->last_applied;
+}
+
+static int damos_va_stat_pmd_entry(pmd_t *pmd, unsigned long addr,
+		unsigned long next, struct mm_walk *walk)
+{
+	struct damos_va_stat_private *priv = walk->private;
+	struct damos *s = priv->scheme;
+	unsigned long *sz_filter_passed = priv->sz_filter_passed;
+	struct vm_area_struct *vma = walk->vma;
+	struct folio *folio;
+	spinlock_t *ptl;
+	pte_t *start_pte, *pte, ptent;
+	int nr;
+
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+	if (pmd_trans_huge(*pmd)) {
+		pmd_t pmde;
+
+		ptl = pmd_trans_huge_lock(pmd, vma);
+		if (!ptl)
+			return 0;
+		pmde = pmdp_get(pmd);
+		if (!pmd_present(pmde))
+			goto huge_unlock;
+
+		folio = vm_normal_folio_pmd(vma, addr, pmde);
+
+		if (damos_va_invalid_folio(folio, s))
+			goto huge_unlock;
+
+		if (!damos_va_filter_out(s, folio, vma, addr, NULL, pmd))
+			*sz_filter_passed += folio_size(folio);
+		s->last_applied = folio;
+
+huge_unlock:
+		spin_unlock(ptl);
+		return 0;
+	}
+#endif
+	start_pte = pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
+	if (!start_pte)
+		return 0;
+
+	for (; addr < next; pte += nr, addr += nr * PAGE_SIZE) {
+		nr = 1;
+		ptent = ptep_get(pte);
+
+		if (pte_none(ptent) || !pte_present(ptent))
+			continue;
+
+		folio = vm_normal_folio(vma, addr, ptent);
+
+		if (damos_va_invalid_folio(folio, s))
+			continue;
+
+		if (!damos_va_filter_out(s, folio, vma, addr, pte, NULL))
+			*sz_filter_passed += folio_size(folio);
+		nr = folio_nr_pages(folio);
+		s->last_applied = folio;
+	}
+	pte_unmap_unlock(start_pte, ptl);
+	return 0;
+}
+
+static unsigned long damos_va_stat(struct damon_target *target,
+		struct damon_region *r, struct damos *s,
+		unsigned long *sz_filter_passed)
+{
+	struct damos_va_stat_private priv;
+	struct mm_struct *mm;
+	struct mm_walk_ops walk_ops = {
+		.pmd_entry = damos_va_stat_pmd_entry,
+		.walk_lock = PGWALK_RDLOCK,
+	};
+
+	priv.scheme = s;
+	priv.sz_filter_passed = sz_filter_passed;
+
+	if (!damos_ops_has_filter(s))
+		return 0;
+
+	mm = damon_get_mm(target);
+	if (!mm)
+		return 0;
+
+	mmap_read_lock(mm);
+	walk_page_range(mm, r->ar.start, r->ar.end, &walk_ops, &priv);
+	mmap_read_unlock(mm);
+	mmput(mm);
+	return 0;
+}
+
 static unsigned long damon_va_apply_scheme(struct damon_ctx *ctx,
 		struct damon_target *t, struct damon_region *r,
 		struct damos *scheme, unsigned long *sz_filter_passed)
@@ -916,7 +1017,7 @@ static unsigned long damon_va_apply_scheme(struct damon_ctx *ctx,
 	case DAMOS_MIGRATE_COLD:
 		return damos_va_migrate(t, r, scheme, sz_filter_passed);
 	case DAMOS_STAT:
-		return 0;
+		return damos_va_stat(t, r, scheme, sz_filter_passed);
 	default:
 		/*
 		 * DAMOS actions that are not yet supported by 'vaddr'.
-- 
2.43.0

On Sat,  2 Aug 2025 11:52:46 +0000 Yueyang Pan <pyyjason@gmail.com> wrote:

> This patch extends DAMOS_STAT handling of the DAMON operations
> sets for virtual address spaces for ops-level DAMOS filters.
> It leverages the walk_page_range to walk the page table and gets
> the folio from page table. The last folio scanned is stored in
> damos->last_applied to prevent double counting.
> 
> Signed-off-by: Yueyang Pan <pyyjason@gmail.com>

Reviewed-by: SeongJae Park <sj@kernel.org>


Thanks,
SJ

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