Message-Id: <20251205071855.72743-40-byungchul@sk.com>
Date: Fri,  5 Dec 2025 16:18:52 +0900
From: Byungchul Park <byungchul@...com>
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Subject: [PATCH v18 39/42] dept: introduce APIs to set page usage and use subclasses_evt for the usage

False positive reports have been observed since dept assumes that all
the pages have the same dept class, but the class should be split since
the call paths are different depending on what the page is used for.

At least, ones for block device and ones for regular file have
exclusively different usages.

Define usage candidates like:

   DEPT_PAGE_REGFILE_CACHE /* page in regular file's address_space */
   DEPT_PAGE_BDEV_CACHE    /* page in block device's address_space */
   DEPT_PAGE_DEFAULT       /* the others */

Introduce APIs to set each page usage properly and make sure not to
interact between DEPT_PAGE_REGFILE_CACHE and DEPT_PAGE_BDEV_CACHE.
Besides that, it allows the other cases:

   interaction between DEPT_PAGE_DEFAULT and DEPT_PAGE_REGFILE_CACHE,
   interaction between DEPT_PAGE_DEFAULT and DEPT_PAGE_BDEV_CACHE,
   interaction between DEPT_PAGE_DEFAULT and DEPT_PAGE_DEFAULT.

Signed-off-by: Byungchul Park <byungchul@...com>
---
 include/linux/dept.h       | 34 ++++++++++++++-
 include/linux/mm_types.h   |  1 +
 include/linux/page-flags.h | 89 +++++++++++++++++++++++++++++++++++++-
 3 files changed, 120 insertions(+), 4 deletions(-)

diff --git a/include/linux/dept.h b/include/linux/dept.h
index 7b822caee874..b3bb1a1a7eb5 100644
--- a/include/linux/dept.h
+++ b/include/linux/dept.h
@@ -19,8 +19,8 @@ struct task_struct;
 #define DEPT_MAX_WAIT_HIST		64
 #define DEPT_MAX_ECXT_HELD		48
 
-#define DEPT_MAX_SUBCLASSES		16
-#define DEPT_MAX_SUBCLASSES_EVT		2
+#define DEPT_MAX_SUBCLASSES		24
+#define DEPT_MAX_SUBCLASSES_EVT		3
 #define DEPT_MAX_SUBCLASSES_USR		(DEPT_MAX_SUBCLASSES / DEPT_MAX_SUBCLASSES_EVT)
 #define DEPT_MAX_SUBCLASSES_CACHE	2
 
@@ -142,6 +142,35 @@ struct dept_ext_wgen {
 	unsigned int wgen;
 };
 
+enum {
+	DEPT_PAGE_DEFAULT = 0,
+	DEPT_PAGE_REGFILE_CACHE,	/* regular file page cache */
+	DEPT_PAGE_BDEV_CACHE,		/* block device cache */
+	DEPT_PAGE_USAGE_NR,		/* nr of usages options */
+};
+
+#define DEPT_PAGE_USAGE_SHIFT 16
+#define DEPT_PAGE_USAGE_MASK ((1U << DEPT_PAGE_USAGE_SHIFT) - 1)
+#define DEPT_PAGE_USAGE_PENDING_MASK (DEPT_PAGE_USAGE_MASK << DEPT_PAGE_USAGE_SHIFT)
+
+/*
+ * Identify each page's usage type
+ */
+struct dept_page_usage {
+	/*
+	 * low 16 bits  : the current usage type
+	 * high 16 bits : usage type requested to be set
+	 *
+	 * Do not apply usage type on request immediately but postpone
+	 * it until the next use of PG flags.  For example, if the page
+	 * is already within a PG_locked critical section, regard it as
+	 * DEPT_PAGE_DEFAULT temporarily at least until the section ends
+	 * e.g. folio_unlock() since it's still unclear which usage type
+	 * the page acts within the section.
+	 */
+	atomic_t type; /* Update and read atomically */
+};
+
 struct dept_event_site {
 	/*
 	 * event site name
@@ -314,6 +343,7 @@ extern void dept_hardirqs_off(void);
 struct dept_key { };
 struct dept_map { };
 struct dept_ext_wgen { };
+struct dept_page_usage { };
 struct dept_event_site { };
 
 #define DEPT_MAP_INITIALIZER(n, k) { }
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 42b6959882b3..85d06073d37b 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -220,6 +220,7 @@ struct page {
 	struct page *kmsan_shadow;
 	struct page *kmsan_origin;
 #endif
+	struct dept_page_usage usage;
 	struct dept_ext_wgen pg_locked_wgen;
 } _struct_page_alignment;
 
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 8ab39823ea31..0b0655354b08 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -204,6 +204,80 @@ enum pageflags {
 
 extern struct dept_map pg_locked_map;
 
+static inline void dept_set_page_usage(struct page *p,
+		unsigned int new_type)
+{
+	/*
+	 * Consider the page as DEPT_PAGE_DEFAULT until the next use of
+	 * PG flags e.g. folio_lock().
+	 */
+	unsigned int type = DEPT_PAGE_DEFAULT;
+
+	if (WARN_ON_ONCE(new_type >= DEPT_PAGE_USAGE_NR))
+		return;
+
+	new_type <<= DEPT_PAGE_USAGE_SHIFT;
+	new_type |= type & DEPT_PAGE_USAGE_MASK;
+	atomic_set(&p->usage.type, new_type);
+}
+
+static inline void dept_set_folio_usage(struct folio *f,
+		unsigned int new_type)
+{
+	dept_set_page_usage(&f->page, new_type);
+}
+
+static inline void dept_reset_page_usage(struct page *p)
+{
+	dept_set_page_usage(p, DEPT_PAGE_DEFAULT);
+}
+
+static inline void dept_reset_folio_usage(struct folio *f)
+{
+	dept_reset_page_usage(&f->page);
+}
+
+static inline void dept_update_page_usage(struct page *p)
+{
+	unsigned int type = atomic_read(&p->usage.type);
+	unsigned int new_type;
+
+retry:
+	new_type = type & DEPT_PAGE_USAGE_PENDING_MASK;
+	new_type >>= DEPT_PAGE_USAGE_SHIFT;
+	new_type |= type & DEPT_PAGE_USAGE_PENDING_MASK;
+
+	/*
+	 * Already updated by others.
+	 */
+	if (type == new_type)
+		return;
+
+	if (!atomic_try_cmpxchg(&p->usage.type, &type, new_type))
+		goto retry;
+}
+
+static inline unsigned long dept_event_flags(struct page *p, bool wait)
+{
+	unsigned int type;
+
+	type = atomic_read(&p->usage.type) & DEPT_PAGE_USAGE_MASK;
+
+	if (WARN_ON_ONCE(type >= DEPT_PAGE_USAGE_NR))
+		return 0;
+
+	/*
+	 * wait
+	 */
+	if (wait)
+		return (1UL << DEPT_PAGE_DEFAULT) | (1UL << type);
+
+	/*
+	 * event
+	 */
+	return 1UL << type;
+}
+
 /*
  * Place the following annotations in its suitable point in code:
  *
@@ -214,20 +288,29 @@ extern struct dept_map pg_locked_map;
 
 static inline void dept_page_set_bit(struct page *p, int bit_nr)
 {
+	dept_update_page_usage(p);
+
 	if (bit_nr == PG_locked)
 		dept_request_event(&pg_locked_map, &p->pg_locked_wgen);
 }
 
 static inline void dept_page_clear_bit(struct page *p, int bit_nr)
 {
+	unsigned long evt_f = dept_event_flags(p, false);
+
 	if (bit_nr == PG_locked)
-		dept_event(&pg_locked_map, 1UL, _RET_IP_, __func__, &p->pg_locked_wgen);
+		dept_event(&pg_locked_map, evt_f, _RET_IP_, __func__, &p->pg_locked_wgen);
 }
 
 static inline void dept_page_wait_on_bit(struct page *p, int bit_nr)
 {
+	unsigned long evt_f;
+
+	dept_update_page_usage(p);
+	evt_f = dept_event_flags(p, true);
+
 	if (bit_nr == PG_locked)
-		dept_wait(&pg_locked_map, 1UL, _RET_IP_, __func__, 0, -1L);
+		dept_wait(&pg_locked_map, evt_f, _RET_IP_, __func__, 0, -1L);
 }
 
 static inline void dept_folio_set_bit(struct folio *f, int bit_nr)
@@ -245,6 +328,8 @@ static inline void dept_folio_wait_on_bit(struct folio *f, int bit_nr)
 	dept_page_wait_on_bit(&f->page, bit_nr);
 }
 #else
+#define dept_set_page_usage(p, t)		do { } while (0)
+#define dept_reset_page_usage(p)		do { } while (0)
 #define dept_page_set_bit(p, bit_nr)		do { } while (0)
 #define dept_page_clear_bit(p, bit_nr)		do { } while (0)
 #define dept_page_wait_on_bit(p, bit_nr)	do { } while (0)
-- 
2.17.1

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