[PATCH RFC 1/9] fs: switch timespec64 fields in inode to discrete integers

[Jeff Layton <jlayton@xxxxxxxxxx>]

This shaves 8 bytes off struct inode with a garden-variety Fedora
Kconfig, but it moves the i_lock into the previous cacheline, away from
the fields it protects. To remedy that, move the i_generation just after
the nanosecond fields, which moves the 4 byte hole down next to
i_fsnotify_mask.

Suggested-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Suggested-by: Amir Goldstein <amir73il@xxxxxxxxx>
Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx>
---
 include/linux/fs.h | 56 +++++++++++++++++++++++++++++++-----------------------
 1 file changed, 32 insertions(+), 24 deletions(-)

diff --git a/include/linux/fs.h b/include/linux/fs.h
index cc29518517f7..78786c1c32fd 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -671,9 +671,13 @@ struct inode {
 	};
 	dev_t			i_rdev;
 	loff_t			i_size;
-	struct timespec64	__i_atime;
-	struct timespec64	__i_mtime;
-	struct timespec64	__i_ctime; /* use inode_*_ctime accessors! */
+	time64_t		i_atime_sec;
+	time64_t		i_mtime_sec;
+	time64_t		i_ctime_sec;
+	u32			i_atime_nsec;
+	u32			i_mtime_nsec;
+	u32			i_ctime_nsec;
+	u32			i_generation;
 	spinlock_t		i_lock;	/* i_blocks, i_bytes, maybe i_size */
 	unsigned short          i_bytes;
 	u8			i_blkbits;
@@ -730,10 +734,10 @@ struct inode {
 		unsigned		i_dir_seq;
 	};
 
-	__u32			i_generation;
 
 #ifdef CONFIG_FSNOTIFY
 	__u32			i_fsnotify_mask; /* all events this inode cares about */
+	/* 32bit hole reserved for expanding i_fsnotify_mask to 64bit */
 	struct fsnotify_mark_connector __rcu	*i_fsnotify_marks;
 #endif
 
@@ -1513,23 +1517,27 @@ struct timespec64 inode_set_ctime_current(struct inode *inode);
 
 static inline time64_t inode_get_atime_sec(const struct inode *inode)
 {
-	return inode->__i_atime.tv_sec;
+	return inode->i_atime_sec;
 }
 
 static inline long inode_get_atime_nsec(const struct inode *inode)
 {
-	return inode->__i_atime.tv_nsec;
+	return inode->i_atime_nsec;
 }
 
 static inline struct timespec64 inode_get_atime(const struct inode *inode)
 {
-	return inode->__i_atime;
+	struct timespec64 ts = { .tv_sec  = inode_get_atime_sec(inode),
+				 .tv_nsec = inode_get_atime_nsec(inode) };
+
+	return ts;
 }
 
 static inline struct timespec64 inode_set_atime_to_ts(struct inode *inode,
 						      struct timespec64 ts)
 {
-	inode->__i_atime = ts;
+	inode->i_atime_sec = ts.tv_sec;
+	inode->i_atime_nsec = ts.tv_nsec;
 	return ts;
 }
 
@@ -1538,28 +1546,32 @@ static inline struct timespec64 inode_set_atime(struct inode *inode,
 {
 	struct timespec64 ts = { .tv_sec  = sec,
 				 .tv_nsec = nsec };
+
 	return inode_set_atime_to_ts(inode, ts);
 }
 
 static inline time64_t inode_get_mtime_sec(const struct inode *inode)
 {
-	return inode->__i_mtime.tv_sec;
+	return inode->i_mtime_sec;
 }
 
 static inline long inode_get_mtime_nsec(const struct inode *inode)
 {
-	return inode->__i_mtime.tv_nsec;
+	return inode->i_mtime_nsec;
 }
 
 static inline struct timespec64 inode_get_mtime(const struct inode *inode)
 {
-	return inode->__i_mtime;
+	struct timespec64 ts = { .tv_sec  = inode_get_mtime_sec(inode),
+				 .tv_nsec = inode_get_mtime_nsec(inode) };
+	return ts;
 }
 
 static inline struct timespec64 inode_set_mtime_to_ts(struct inode *inode,
 						      struct timespec64 ts)
 {
-	inode->__i_mtime = ts;
+	inode->i_mtime_sec = ts.tv_sec;
+	inode->i_mtime_nsec = ts.tv_nsec;
 	return ts;
 }
 
@@ -1573,34 +1585,30 @@ static inline struct timespec64 inode_set_mtime(struct inode *inode,
 
 static inline time64_t inode_get_ctime_sec(const struct inode *inode)
 {
-	return inode->__i_ctime.tv_sec;
+	return inode->i_ctime_sec;
 }
 
 static inline long inode_get_ctime_nsec(const struct inode *inode)
 {
-	return inode->__i_ctime.tv_nsec;
+	return inode->i_ctime_nsec;
 }
 
 static inline struct timespec64 inode_get_ctime(const struct inode *inode)
 {
-	return inode->__i_ctime;
+	struct timespec64 ts = { .tv_sec  = inode_get_ctime_sec(inode),
+				 .tv_nsec = inode_get_ctime_nsec(inode) };
+
+	return ts;
 }
 
 static inline struct timespec64 inode_set_ctime_to_ts(struct inode *inode,
 						      struct timespec64 ts)
 {
-	inode->__i_ctime = ts;
+	inode->i_ctime_sec = ts.tv_sec;
+	inode->i_ctime_nsec = ts.tv_nsec;
 	return ts;
 }
 
-/**
- * inode_set_ctime - set the ctime in the inode
- * @inode: inode in which to set the ctime
- * @sec: tv_sec value to set
- * @nsec: tv_nsec value to set
- *
- * Set the ctime in @inode to { @sec, @nsec }
- */
 static inline struct timespec64 inode_set_ctime(struct inode *inode,
 						time64_t sec, long nsec)
 {

-- 
2.41.0