My friend Akkana followed my advice to use noatime on one of her
machines, but discovered that mutt was unusable because it always
thought that new messages had arrived since the last time it had
checked a folder (mbox format). I thought this was a bummer, so I
wrote a "relative lazy atime" patch which only updates the atime if
the old atime was less than the ctime or mtime. This is not the same
as the lazy atime patch of yore[1], which maintained a list of inodes
with dirty atimes and wrote them out on unmount.
Patch below. Current version (plus test program) is at:
http://infohost.nmt.edu/~val/patches.html#lazyatime
Thanks to everyone who discussed this with me, especially the folks on
#linuxfs on irc.oftc.net.
-VAL
[1] http://www.ussg.iu.edu/hypermail/linux/kernel/0005.0/0284.html
---
Relative lazy atime - only update atime if the old atime was older
than the ctime or mtime. We are maintaining atime relative to
mtime/ctime.
Not for inclusion (yet).
Written by Val Henson <[email protected]>
fs/inode.c | 16 +++++++++++++++-
fs/namespace.c | 5 ++++-
include/linux/fs.h | 1 +
include/linux/mount.h | 1 +
4 files changed, 21 insertions(+), 2 deletions(-)
diff -Nrup a/fs/inode.c b/fs/inode.c
--- a/fs/inode.c 2006-08-02 23:10:56 -07:00
+++ b/fs/inode.c 2006-08-02 23:10:56 -07:00
@@ -1200,10 +1200,24 @@ void touch_atime(struct vfsmount *mnt, s
return;
now = current_fs_time(inode->i_sb);
- if (!timespec_equal(&inode->i_atime, &now)) {
+ if (timespec_equal(&inode->i_atime, &now))
+ return;
+ /*
+ * With lazy atime, only update atime if the previous atime is
+ * earlier than either the ctime or mtime.
+ */
+ if (!mnt ||
+ !(mnt->mnt_flags & MNT_LAZYATIME) ||
+ (timespec_compare(&inode->i_atime, &inode->i_mtime) < 0) ||
+ (timespec_compare(&inode->i_atime, &inode->i_ctime) < 0)) {
inode->i_atime = now;
mark_inode_dirty_sync(inode);
}
+ /*
+ * We could update the in-memory atime here if we wanted, but
+ * that makes it possible for atime to revert if we evict the
+ * inode from memory.
+ */
}
EXPORT_SYMBOL(touch_atime);
diff -Nrup a/fs/namespace.c b/fs/namespace.c
--- a/fs/namespace.c 2006-08-02 23:10:56 -07:00
+++ b/fs/namespace.c 2006-08-02 23:10:56 -07:00
@@ -376,6 +376,7 @@ static int show_vfsmnt(struct seq_file *
{ MNT_NOEXEC, ",noexec" },
{ MNT_NOATIME, ",noatime" },
{ MNT_NODIRATIME, ",nodiratime" },
+ { MNT_LAZYATIME, ",lazyatime" },
{ 0, NULL }
};
struct proc_fs_info *fs_infop;
@@ -1413,9 +1414,11 @@ long do_mount(char *dev_name, char *dir_
mnt_flags |= MNT_NOATIME;
if (flags & MS_NODIRATIME)
mnt_flags |= MNT_NODIRATIME;
+ if (flags & MS_LAZYATIME)
+ mnt_flags |= MNT_LAZYATIME;
flags &= ~(MS_NOSUID | MS_NOEXEC | MS_NODEV | MS_ACTIVE |
- MS_NOATIME | MS_NODIRATIME);
+ MS_NOATIME | MS_NODIRATIME | MS_LAZYATIME);
/* ... and get the mountpoint */
retval = path_lookup(dir_name, LOOKUP_FOLLOW, &nd);
diff -Nrup a/include/linux/fs.h b/include/linux/fs.h
--- a/include/linux/fs.h 2006-08-02 23:10:56 -07:00
+++ b/include/linux/fs.h 2006-08-02 23:10:56 -07:00
@@ -119,6 +119,7 @@ extern int dir_notify_enable;
#define MS_PRIVATE (1<<18) /* change to private */
#define MS_SLAVE (1<<19) /* change to slave */
#define MS_SHARED (1<<20) /* change to shared */
+#define MS_LAZYATIME (1<<21) /* Lazily update on-disk access times. */
#define MS_ACTIVE (1<<30)
#define MS_NOUSER (1<<31)
diff -Nrup a/include/linux/mount.h b/include/linux/mount.h
--- a/include/linux/mount.h 2006-08-02 23:10:56 -07:00
+++ b/include/linux/mount.h 2006-08-02 23:10:56 -07:00
@@ -27,6 +27,7 @@ struct namespace;
#define MNT_NOEXEC 0x04
#define MNT_NOATIME 0x08
#define MNT_NODIRATIME 0x10
+#define MNT_LAZYATIME 0x20
#define MNT_SHRINKABLE 0x100
On Wed, Aug 02, 2006 at 11:29:45PM -0700, Valerie Henson wrote:
> My friend Akkana followed my advice to use noatime on one of her
> machines, but discovered that mutt was unusable because it always
> thought that new messages had arrived since the last time it had
> checked a folder (mbox format). I thought this was a bummer, so I
> wrote a "relative lazy atime" patch which only updates the atime if
> the old atime was less than the ctime or mtime. This is not the same
> as the lazy atime patch of yore[1], which maintained a list of inodes
> with dirty atimes and wrote them out on unmount.
This also happens to be useful for file systems such as Unionfs and (from
what I hear) ocfs2 where atime updates can be costly at times.
> Patch below. Current version (plus test program) is at:
Looks fine IMHO.
Josef "Jeff" Sipek.
--
I'm somewhere between geek and normal.
- Linus Torvalds