[RFC PATCH 2/8] mm: Add PG_atomic

Ojaswin Mujoo
2025-11-12T11:07:25Z

From: John Garry <john.g.garry@oracle.com>

Add page flag PG_atomic, meaning that a folio needs to be written back
atomically. This will be used by for handling RWF_ATOMIC buffered IO
in upcoming patches.

Co-developed-by: Ojaswin Mujoo <ojaswin@linux.ibm.com>
Signed-off-by: Ojaswin Mujoo <ojaswin@linux.ibm.com>
Signed-off-by: John Garry <john.g.garry@oracle.com>
---
include/linux/page-flags.h | 5 +++++
include/trace/events/mmflags.h | 3 ++-
2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 0091ad1986bf..bdce0f58a77a 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -111,6 +111,7 @@ enum pageflags {
PG_swapbacked, /* Page is backed by RAM/swap */
PG_unevictable, /* Page is "unevictable" */
PG_dropbehind, /* drop pages on IO completion */
+ PG_atomic, /* Page is marked atomic for buffered atomic writes */
#ifdef CONFIG_MMU
PG_mlocked, /* Page is vma mlocked */
#endif
@@ -644,6 +645,10 @@ FOLIO_FLAG(unevictable, FOLIO_HEAD_PAGE)
__FOLIO_CLEAR_FLAG(unevictable, FOLIO_HEAD_PAGE)
FOLIO_TEST_CLEAR_FLAG(unevictable, FOLIO_HEAD_PAGE)

+FOLIO_FLAG(atomic, FOLIO_HEAD_PAGE)
+ __FOLIO_CLEAR_FLAG(atomic, FOLIO_HEAD_PAGE)
+ FOLIO_TEST_CLEAR_FLAG(atomic, FOLIO_HEAD_PAGE)
+
#ifdef CONFIG_MMU
FOLIO_FLAG(mlocked, FOLIO_HEAD_PAGE)
__FOLIO_CLEAR_FLAG(mlocked, FOLIO_HEAD_PAGE)
diff --git a/include/trace/events/mmflags.h b/include/trace/events/mmflags.h
index aa441f593e9a..a8294f6146a5 100644
--- a/include/trace/events/mmflags.h
+++ b/include/trace/events/mmflags.h
@@ -159,7 +159,8 @@ TRACE_DEFINE_ENUM(___GFP_LAST_BIT);
DEF_PAGEFLAG_NAME(reclaim), \
DEF_PAGEFLAG_NAME(swapbacked), \
DEF_PAGEFLAG_NAME(unevictable), \
- DEF_PAGEFLAG_NAME(dropbehind) \
+ DEF_PAGEFLAG_NAME(dropbehind), \
+ DEF_PAGEFLAG_NAME(atomic) \
IF_HAVE_PG_MLOCK(mlocked) \
IF_HAVE_PG_HWPOISON(hwpoison) \
IF_HAVE_PG_IDLE(idle) \
--
2.51.0