3 files changed, 61 insertions, 9 deletions

diff --git a/module/zfs/zfs_vfsops.c b/module/zfs/zfs_vfsops.c
index 781708ba9..18194a5dc 100644
--- a/module/zfs/zfs_vfsops.c
+++ b/module/zfs/zfs_vfsops.c
@@ -303,7 +303,21 @@ zfs_sync(struct super_block *sb, int wait, cred_t *cr)
 static void
 atime_changed_cb(void *arg, uint64_t newval)
 {
-	((zfsvfs_t *)arg)->z_atime = newval;
+	zfsvfs_t *zfsvfs = arg;
+	struct super_block *sb = zfsvfs->z_sb;
+
+	if (sb == NULL)
+		return;
+	/*
+	 * Update SB_NOATIME bit in VFS super block.  Since atime update is
+	 * determined by atime_needs_update(), atime_needs_update() needs to
+	 * return false if atime is turned off, and not unconditionally return
+	 * false if atime is turned on.
+	 */
+	if (newval)
+		sb->s_flags &= ~SB_NOATIME;
+	else
+		sb->s_flags |= SB_NOATIME;
 }
 
 static void
diff --git a/module/zfs/zfs_znode.c b/module/zfs/zfs_znode.c
index d998e42ab..77eb8bb91 100644
--- a/module/zfs/zfs_znode.c
+++ b/module/zfs/zfs_znode.c
@@ -1345,16 +1345,39 @@ zfs_zinactive(znode_t *zp)
 	zfs_znode_hold_exit(zfsvfs, zh);
 }
 
-static inline int
-zfs_compare_timespec(struct timespec *t1, struct timespec *t2)
+#if defined(HAVE_INODE_TIMESPEC64_TIMES)
+#define	zfs_compare_timespec timespec64_compare
+#else
+#define	zfs_compare_timespec timespec_compare
+#endif
+
+/*
+ * Determine whether the znode's atime must be updated.  The logic mostly
+ * duplicates the Linux kernel's relatime_need_update() functionality.
+ * This function is only called if the underlying filesystem actually has
+ * atime updates enabled.
+ */
+boolean_t
+zfs_relatime_need_update(const struct inode *ip)
 {
-	if (t1->tv_sec < t2->tv_sec)
-		return (-1);
+	inode_timespec_t now;
+
+	gethrestime(&now);
+	/*
+	 * In relatime mode, only update the atime if the previous atime
+	 * is earlier than either the ctime or mtime or if at least a day
+	 * has passed since the last update of atime.
+	 */
+	if (zfs_compare_timespec(&ip->i_mtime, &ip->i_atime) >= 0)
+		return (B_TRUE);
+
+	if (zfs_compare_timespec(&ip->i_ctime, &ip->i_atime) >= 0)
+		return (B_TRUE);
 
-	if (t1->tv_sec > t2->tv_sec)
-		return (1);
+	if ((hrtime_t)now.tv_sec - (hrtime_t)ip->i_atime.tv_sec >= 24*60*60)
+		return (B_TRUE);
 
-	return (t1->tv_nsec - t2->tv_nsec);
+	return (B_FALSE);
 }
 
 /*
diff --git a/module/zfs/zpl_file.c b/module/zfs/zpl_file.c
index 9c231d950..731836c2c 100644
--- a/module/zfs/zpl_file.c
+++ b/module/zfs/zpl_file.c
@@ -289,6 +289,8 @@ zpl_iter_read_common(struct kiocb *kiocb, const struct iovec *iovp,
 {
 	cred_t *cr = CRED();
 	struct file *filp = kiocb->ki_filp;
+	struct inode *ip = filp->f_mapping->host;
+	zfsvfs_t *zfsvfs = ZTOZSB(ITOZ(ip));
 	ssize_t read;
 	unsigned int f_flags = filp->f_flags;
 
@@ -298,7 +300,20 @@ zpl_iter_read_common(struct kiocb *kiocb, const struct iovec *iovp,
 	    nr_segs, &kiocb->ki_pos, seg, f_flags, cr, skip);
 	crfree(cr);
 
-	file_accessed(filp);
+	/*
+	 * If relatime is enabled, call file_accessed() only if
+	 * zfs_relatime_need_update() is true.  This is needed since datasets
+	 * with inherited "relatime" property aren't necessarily mounted with
+	 * MNT_RELATIME flag (e.g. after `zfs set relatime=...`), which is what
+	 * relatime test in VFS by relatime_need_update() is based on.
+	 */
+	if (!IS_NOATIME(ip) && zfsvfs->z_relatime) {
+		if (zfs_relatime_need_update(ip))
+			file_accessed(filp);
+	} else {
+		file_accessed(filp);
+	}
+
 	return (read);
 }