+ mm-damon-vaddr-respect-folio-end-for-damos_stat.patch added to mm-new branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: mm/damon/vaddr: respect folio end for DAMOS_STAT
has been added to the -mm mm-new branch.  Its filename is
     mm-damon-vaddr-respect-folio-end-for-damos_stat.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-damon-vaddr-respect-folio-end-for-damos_stat.patch

This patch will later appear in the mm-new branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Note, mm-new is a provisional staging ground for work-in-progress
patches, and acceptance into mm-new is a notification for others take
notice and to finish up reviews.  Please do not hesitate to respond to
review feedback and post updated versions to replace or incrementally
fixup patches in mm-new.

The mm-new branch of mm.git is not included in linux-next

If a few days of testing in mm-new is successful, the patch will me moved
into mm.git's mm-unstable branch, which is included in linux-next

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------------------------------------------------------
From: SJ Park <sj@kernel.org>
Subject: mm/damon/vaddr: respect folio end for DAMOS_STAT
Date: Tue, 1 Sep 2026 06:18:45 -0700

For applying DAMOS_STAT action to a region, DAMON virtual address space
operation set (vaddr) calls walk_page_range[_vma]() for the region.  The
pmd walk entry function, namely damon_va_stat_pmd_entry(), applies DAMOS
filters to folios of addresses of the region in the pmd.  It starts from
the walking address and advances the address by the size of the folio of
the address until it goes out of the pmd or the region.

Let's suppose it is for the first pmd of the region, and the region start
address is in the middle of a large folio.  Also, the next folios are
small.  Then, some of the next folios could be skipped.  Fix the issue by
advancing the address to exactly the start address of the next folio.

The user impact is that the DAMOS_STAT-based page level monitoring results
become inaccurate.  Since the page level monitoring is supposed to provide
relatively high precision, this is definitely a problem.  It is arguably
not critical since it is only monitoring quality degradation.

The issue was discovered [1] by Sashiko.

Link: https://lore.kernel.org/20260901131850.98037-5-sj@kernel.org
Link: https://lore.kernel.org/20260514015053.149396-1-sj@kernel.org [1]
Fixes: 63f39737d1e3 ("mm/damon/vaddr: support stat-purpose DAMOS filters")
Signed-off-by: SJ Park <sj@kernel.org>
Cc: Usama Arif <usamaarif642@gmail.com>
Cc: <stable@vger.kernel.org> # 6.18.x
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/damon/vaddr.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

--- a/mm/damon/vaddr.c~mm-damon-vaddr-respect-folio-end-for-damos_stat
+++ a/mm/damon/vaddr.c
@@ -831,6 +831,8 @@ huge_unlock:
 		return 0;
 
 	for (; addr < next; pte += nr, addr += nr * PAGE_SIZE) {
+		unsigned long page_idx;
+
 		nr = 1;
 		ptent = ptep_get(pte);
 
@@ -844,7 +846,8 @@ huge_unlock:
 
 		if (!damos_va_filter_out(s, folio, vma, addr, pte, NULL))
 			*sz_filter_passed += folio_size(folio);
-		nr = folio_nr_pages(folio);
+		page_idx = folio_page_idx(folio, pte_page(ptent));
+		nr = folio_nr_pages(folio) - page_idx;
 		s->last_applied = folio;
 	}
 	pte_unmap_unlock(start_pte, ptl);
_

Patches currently in -mm which might be from sj@kernel.org are

mm-damon-core-skip-applying-scheme-if-region-split-for-quota-fails.patch
mm-damon-paddr-respect-folio-end-for-damos_stat.patch
mm-damon-paddr-respect-folio-end-for-damos-actions-except-stat.patch
mm-damon-vaddr-respect-folio-end-for-damos_stat.patch
mm-damon-vaddr-respect-folio-end-for-damos_migrate_hotcold.patch
mm-damon-core-handle-extreme-memory-state-in-damon_get_node_mem_bp.patch
mm-damon-core-handle-extreme-memory-state-in-get_node_memcg_used_bp.patch
mm-damon-core-handle-extreme-memory-state-in-get_in_active_mem_bp.patch