[PATCH v2 2/5] fanotify: reduce event objectid to 29-bit hash

[Amir Goldstein <amir73il@gmail.com>]

objectid is only used by fanotify backend and it is just an optimization
for event merge before comparing all fields in event.

Move the objectid member from common struct fsnotify_event into struct
fanotify_event and reduce it to 29-bit hash to cram it together with the
3-bit event type.

Events of different types are never merged, so the combination of event
type and hash form a 32-bit key for fast compare of events.

This reduces the size of events by one pointer and paves the way for
adding hashed queue support for fanotify.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
---
 fs/notify/fanotify/fanotify.c        | 25 ++++++++++++-------------
 fs/notify/fanotify/fanotify.h        | 16 +++++++++++++---
 fs/notify/inotify/inotify_fsnotify.c |  2 +-
 fs/notify/inotify/inotify_user.c     |  2 +-
 include/linux/fsnotify_backend.h     |  5 +----
 5 files changed, 28 insertions(+), 22 deletions(-)

diff --git a/fs/notify/fanotify/fanotify.c b/fs/notify/fanotify/fanotify.c
index 1192c9953620..8a2bb6954e02 100644
--- a/fs/notify/fanotify/fanotify.c
+++ b/fs/notify/fanotify/fanotify.c
@@ -88,16 +88,12 @@ static bool fanotify_name_event_equal(struct fanotify_name_event *fne1,
 	return fanotify_info_equal(info1, info2);
 }
 
-static bool fanotify_should_merge(struct fsnotify_event *old_fsn,
-				  struct fsnotify_event *new_fsn)
+static bool fanotify_should_merge(struct fanotify_event *old,
+				  struct fanotify_event *new)
 {
-	struct fanotify_event *old, *new;
+	pr_debug("%s: old=%p new=%p\n", __func__, old, new);
 
-	pr_debug("%s: old=%p new=%p\n", __func__, old_fsn, new_fsn);
-	old = FANOTIFY_E(old_fsn);
-	new = FANOTIFY_E(new_fsn);
-
-	if (old_fsn->objectid != new_fsn->objectid ||
+	if (old->hash != new->hash ||
 	    old->type != new->type || old->pid != new->pid)
 		return false;
 
@@ -133,10 +129,9 @@ static bool fanotify_should_merge(struct fsnotify_event *old_fsn,
 static int fanotify_merge(struct list_head *list, struct fsnotify_event *event)
 {
 	struct fsnotify_event *test_event;
-	struct fanotify_event *new;
+	struct fanotify_event *old, *new = FANOTIFY_E(event);
 
 	pr_debug("%s: list=%p event=%p\n", __func__, list, event);
-	new = FANOTIFY_E(event);
 
 	/*
 	 * Don't merge a permission event with any other event so that we know
@@ -147,8 +142,9 @@ static int fanotify_merge(struct list_head *list, struct fsnotify_event *event)
 		return 0;
 
 	list_for_each_entry_reverse(test_event, list, list) {
-		if (fanotify_should_merge(test_event, event)) {
-			FANOTIFY_E(test_event)->mask |= new->mask;
+		old = FANOTIFY_E(test_event);
+		if (fanotify_should_merge(old, new)) {
+			old->mask |= new->mask;
 			return 1;
 		}
 	}
@@ -533,6 +529,7 @@ static struct fanotify_event *fanotify_alloc_event(struct fsnotify_group *group,
 	struct mem_cgroup *old_memcg;
 	struct inode *child = NULL;
 	bool name_event = false;
+	unsigned int hash = 0;
 
 	if ((fid_mode & FAN_REPORT_DIR_FID) && dirid) {
 		/*
@@ -600,8 +597,10 @@ static struct fanotify_event *fanotify_alloc_event(struct fsnotify_group *group,
 	 * Use the victim inode instead of the watching inode as the id for
 	 * event queue, so event reported on parent is merged with event
 	 * reported on child when both directory and child watches exist.
+	 * Hash object id for queue merge.
 	 */
-	fanotify_init_event(event, (unsigned long)id, mask);
+	hash = hash_ptr(id, FANOTIFY_EVENT_HASH_BITS);
+	fanotify_init_event(event, hash, mask);
 	if (FAN_GROUP_FLAG(group, FAN_REPORT_TID))
 		event->pid = get_pid(task_pid(current));
 	else
diff --git a/fs/notify/fanotify/fanotify.h b/fs/notify/fanotify/fanotify.h
index 896c819a1786..d531f0cfa46f 100644
--- a/fs/notify/fanotify/fanotify.h
+++ b/fs/notify/fanotify/fanotify.h
@@ -135,19 +135,29 @@ enum fanotify_event_type {
 	FANOTIFY_EVENT_TYPE_PATH,
 	FANOTIFY_EVENT_TYPE_PATH_PERM,
 	FANOTIFY_EVENT_TYPE_OVERFLOW, /* struct fanotify_event */
+	__FANOTIFY_EVENT_TYPE_NUM
 };
 
+#define FANOTIFY_EVENT_TYPE_BITS \
+	(ilog2(__FANOTIFY_EVENT_TYPE_NUM - 1) + 1)
+#define FANOTIFY_EVENT_HASH_BITS \
+	(32 - FANOTIFY_EVENT_TYPE_BITS)
+
 struct fanotify_event {
 	struct fsnotify_event fse;
 	u32 mask;
-	enum fanotify_event_type type;
+	struct {
+		unsigned int type : FANOTIFY_EVENT_TYPE_BITS;
+		unsigned int hash : FANOTIFY_EVENT_HASH_BITS;
+	};
 	struct pid *pid;
 };
 
 static inline void fanotify_init_event(struct fanotify_event *event,
-				       unsigned long id, u32 mask)
+				       unsigned int hash, u32 mask)
 {
-	fsnotify_init_event(&event->fse, id);
+	fsnotify_init_event(&event->fse);
+	event->hash = hash;
 	event->mask = mask;
 	event->pid = NULL;
 }
diff --git a/fs/notify/inotify/inotify_fsnotify.c b/fs/notify/inotify/inotify_fsnotify.c
index 1901d799909b..0533bacbd584 100644
--- a/fs/notify/inotify/inotify_fsnotify.c
+++ b/fs/notify/inotify/inotify_fsnotify.c
@@ -107,7 +107,7 @@ int inotify_handle_inode_event(struct fsnotify_mark *inode_mark, u32 mask,
 		mask &= ~IN_ISDIR;
 
 	fsn_event = &event->fse;
-	fsnotify_init_event(fsn_event, 0);
+	fsnotify_init_event(fsn_event);
 	event->mask = mask;
 	event->wd = i_mark->wd;
 	event->sync_cookie = cookie;
diff --git a/fs/notify/inotify/inotify_user.c b/fs/notify/inotify/inotify_user.c
index a6c95bd64618..98f61b31745a 100644
--- a/fs/notify/inotify/inotify_user.c
+++ b/fs/notify/inotify/inotify_user.c
@@ -641,7 +641,7 @@ static struct fsnotify_group *inotify_new_group(unsigned int max_events)
 		return ERR_PTR(-ENOMEM);
 	}
 	group->overflow_event = &oevent->fse;
-	fsnotify_init_event(group->overflow_event, 0);
+	fsnotify_init_event(group->overflow_event);
 	oevent->mask = FS_Q_OVERFLOW;
 	oevent->wd = -1;
 	oevent->sync_cookie = 0;
diff --git a/include/linux/fsnotify_backend.h b/include/linux/fsnotify_backend.h
index 7eb979bfc141..fc98f9f88d12 100644
--- a/include/linux/fsnotify_backend.h
+++ b/include/linux/fsnotify_backend.h
@@ -167,7 +167,6 @@ struct fsnotify_ops {
  */
 struct fsnotify_event {
 	struct list_head list;
-	unsigned long objectid;	/* identifier for queue merges */
 };
 
 /*
@@ -582,11 +581,9 @@ extern void fsnotify_put_mark(struct fsnotify_mark *mark);
 extern void fsnotify_finish_user_wait(struct fsnotify_iter_info *iter_info);
 extern bool fsnotify_prepare_user_wait(struct fsnotify_iter_info *iter_info);
 
-static inline void fsnotify_init_event(struct fsnotify_event *event,
-				       unsigned long objectid)
+static inline void fsnotify_init_event(struct fsnotify_event *event)
 {
 	INIT_LIST_HEAD(&event->list);
-	event->objectid = objectid;
 }
 
 #else
-- 
2.30.0