[RFC PATCH 6.12.y 2/5] mm/damon/paddr: respect folio end for DAMOS actions except STAT

[SJ Park <sj@kernel.org>]

A few functions for applying DAMOS actions including pageout, lru_[de]prio
and migrate_{hot,cold} in DAMON physical address space operation set
(paddr) collect folios of the given region by getting the folios of
region-internal addresses.  Then, those functions apply the action to the
collected folios at once.  The collection starts from the region start
address and advances the address by the size of the folio of the address
until it goes out of the region.  If the start address is in the middle of
a large folio, and if the next folios are small, 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 DAMOS action is applied to less than expected
amount of memory.  Given the best effort nature of DAMON, it is no big
problem, but it is clearly a bug that is better to be fixed.

The issue was discovered [1] by Sashiko.

Link: https://lore.kernel.org/20260901131850.98037-4-sj@kernel.org
Link: https://lore.kernel.org/20260517234112.89245-1-sj@kernel.org [1]
Fixes: 3a06696305e7 ("mm/damon/ops: have damon_get_folio return folio even for tail pages")
Signed-off-by: SJ Park <sj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Usama Arif <usamaarif642@gmail.com>
Cc: <stable@vger.kernel.org> # 6.15.x
(cherry picked from commit 1613ac9edf385c35f171a25610e2706a7e6afad6)
---
 mm/damon/paddr.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/mm/damon/paddr.c b/mm/damon/paddr.c
index a6b1de97b1e8a..6bac269cd679e 100644
--- a/mm/damon/paddr.c
+++ b/mm/damon/paddr.c
@@ -273,7 +273,7 @@ static unsigned long damon_pa_pageout(struct damon_region *r, struct damos *s)
 		else
 			list_add(&folio->lru, &folio_list);
 put_folio:
-		addr += folio_size(folio);
+		addr = PFN_PHYS(folio_pfn(folio)) + folio_size(folio);
 		folio_put(folio);
 	}
 	if (install_young_filter)
@@ -306,7 +306,7 @@ static inline unsigned long damon_pa_mark_accessed_or_deactivate(
 			folio_deactivate(folio);
 		applied += folio_nr_pages(folio);
 put_folio:
-		addr += folio_size(folio);
+		addr = PFN_PHYS(folio_pfn(folio)) + folio_size(folio);
 		folio_put(folio);
 	}
 	return applied * PAGE_SIZE;
@@ -483,7 +483,7 @@ static unsigned long damon_pa_migrate(struct damon_region *r, struct damos *s)
 				folio_is_file_lru(folio));
 		list_add(&folio->lru, &folio_list);
 put_folio:
-		addr += folio_size(folio);
+		addr = PFN_PHYS(folio_pfn(folio)) + folio_size(folio);
 		folio_put(folio);
 	}
 	applied = damon_pa_migrate_pages(&folio_list, s->target_nid);
-- 
2.47.3