mm/damon/ops: have damon_get_folio return folio even for tail pages

Patch series "mm/damon/paddr: fix large folios access and schemes handling".

DAMON operations set for physical address space, namely 'paddr', treats
tail pages as unaccessed always.  It can also apply DAMOS action to a
large folio multiple times within single DAMOS' regions walking.  As a
result, the monitoring output has poor quality and DAMOS works in
unexpected ways when large folios are being used.  Fix those.

The patches were parts of Usama's hugepage_size DAMOS filter patch
series[1].  The first fix has collected from there with a slight commit
message change for the subject prefix.  The second fix is re-written by SJ
and posted as an RFC before this series.  The second one also got a slight
commit message change for the subject prefix.

[1] https://lore.kernel.org/20250203225604.44742-1-usamaarif642@gmail.com
[2] https://lore.kernel.org/20250206231103.38298-1-sj@kernel.org


This patch (of 2):

This effectively adds support for large folios in damon for paddr, as
damon_pa_mkold/young won't get a null folio from this function and won't
ignore it, hence access will be checked and reported.  This also means
that larger folios will be considered for different DAMOS actions like
pageout, prioritization and migration.  As these DAMOS actions will
consider larger folios, iterate through the region at folio_size and not
PAGE_SIZE intervals.  This should not have an affect on vaddr, as
damon_young_pmd_entry considers pmd entries.

Link: https://lkml.kernel.org/r/20250207212033.45269-1-sj@kernel.org
Link: https://lkml.kernel.org/r/20250207212033.45269-2-sj@kernel.org
Fixes: a28397beb55b ("mm/damon: implement primitives for physical address space monitoring")
Signed-off-by: Usama Arif <usamaarif642@gmail.com>
Signed-off-by: SeongJae Park <sj@kernel.org>
Reviewed-by: SeongJae Park <sj@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 1 insertions, 1 deletions

diff --git a/mm/damon/ops-common.c b/mm/damon/ops-common.c
index 86a50e8fbc80..0db1fc70c84d 100644
--- a/mm/damon/ops-common.c
+++ b/mm/damon/ops-common.c
@@ -26,7 +26,7 @@ struct folio *damon_get_folio(unsigned long pfn)
 	struct page *page = pfn_to_online_page(pfn);
 	struct folio *folio;
 
-	if (!page || PageTail(page))
+	if (!page)
 		return NULL;
 
 	folio = page_folio(page);