Re: [PATCH 00/23] per device dirty throttling -v8

Ingo Molnar
2007-08-05T19:09:28Z

* Linus Torvalds <torvalds@linux-foundation.org> wrote:

> On Sun, 5 Aug 2007, Ingo Molnar wrote:
> >
> > you mean tmpwatch? The trivial change below fixes this. And with that
> > we've come to the end of an extremely short list of atime dependencies.
>
> You wouldn't even need these kinds of games.
>
> What we could do is to make "relatime" updates a bit smarter.
>
> A bit smarter would be:
>
> - update atime if the old atime is <= than mtime/ctime
>
> Logic: things like mailers can care about whether some new state has
> been read or not. This is the current relatime.
>
> - update atime if the old atime is more than X seconds in the past
> (defaulting to one day or something)
>
> Logic: things like tmpwatch and backup software may want to remove
> stuff that hasn't been touched in a long time, but they sure don't care
> about "exact" atime.

ok, i've implemented this and it's working fine. Check out the
relatime_need_update() function for the details of the logic. Atime
update frequency is 1 day with that, and we update at least once after
every modification as well, for the mailer logic.

tested it by moving the date forward:

# date
Sun Aug 5 22:55:14 CEST 2007
# date -s "Tue Aug 7 22:55:14 CEST 2007"
Tue Aug 7 22:55:14 CEST 2007

access to a file did not generate disk IO before the date was set, and
it generated exactly one IO after the date was set.

( should i perhaps reduce the number of boot options and only use a
single "norelatime_default" boot option to turn this off? )

Ingo

------------------------------------>
Subject: [patch] add norelatime/relatime boot options, CONFIG_DEFAULT_RELATIME
From: Ingo Molnar <mingo@elte.hu>

change relatime updates to be performed once per day. This makes
relatime a compatible solution for HSM, mailer-notification and
tmpwatch applications too.

also add the CONFIG_DEFAULT_RELATIME kernel option, which makes
"norelatime" the default for all mounts without an extra kernel
boot option.

add the "norelatime" (and "relatime") boot options to enable/disable
relatime updates for all filesystems.

also add the /proc/sys/kernel/mount_with_relatime flag which can be changed
runtime to modify the behavior of subsequent new mounts.

tested by moving the date forward:

# date
Sun Aug 5 22:55:14 CEST 2007
# date -s "Tue Aug 7 22:55:14 CEST 2007"
Tue Aug 7 22:55:14 CEST 2007

access to a file did not generate disk IO before the date was set, and
it generated exactly one IO after the date was set.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
Documentation/kernel-parameters.txt | 12 +++++++
fs/Kconfig | 17 ++++++++++
fs/inode.c | 48 ++++++++++++++++++++--------
fs/namespace.c | 61 ++++++++++++++++++++++++++++++++++++
include/linux/mount.h | 2 +
kernel/sysctl.c | 9 +++++
6 files changed, 136 insertions(+), 13 deletions(-)

Index: linux/Documentation/kernel-parameters.txt
===================================================================
--- linux.orig/Documentation/kernel-parameters.txt
+++ linux/Documentation/kernel-parameters.txt
@@ -303,6 +303,12 @@ and is between 256 and 4096 characters.

atascsi= [HW,SCSI] Atari SCSI

+ relatime [FS] default to enabled relatime updates on all
+ filesystems.
+
+ relatime= [FS] default to enabled/disabled relatime updates on
+ all filesystems.
+
atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
EzKey and similar keyboards

@@ -1100,6 +1106,12 @@ and is between 256 and 4096 characters.
noasync [HW,M68K] Disables async and sync negotiation for
all devices.

+ norelatime [FS] default to disabled relatime updates on all
+ filesystems.
+
+ norelatime= [FS] default to disabled/enabled relatime updates
+ on all filesystems.
+
nobats [PPC] Do not use BATs for mapping kernel lowmem
on "Classic" PPC cores.

Index: linux/fs/Kconfig
===================================================================
--- linux.orig/fs/Kconfig
+++ linux/fs/Kconfig
@@ -2060,6 +2060,23 @@ config 9P_FS

endmenu

+config DEFAULT_RELATIME
+ bool "Mount all filesystems with relatime by default"
+ default y
+ help
+ If you say Y here, all your filesystems will be mounted
+ with the "relatime" mount option. This eliminates many atime
+ ('file last accessed' timestamp) updates (which otherwise
+ is performed on every file access and generates a write
+ IO to the inode) and thus speeds up IO. Atime is still updated,
+ but only once per day.
+
+ The mtime ('file last modified') and ctime ('file created')
+ timestamp are unaffected by this change.
+
+ Use the "norelatime" kernel boot option to turn off this
+ feature.
+
if BLOCK
menu "Partition Types"

Index: linux/fs/inode.c
===================================================================
--- linux.orig/fs/inode.c
+++ linux/fs/inode.c
@@ -1162,6 +1162,36 @@ sector_t bmap(struct inode * inode, sect
}
EXPORT_SYMBOL(bmap);

+/*
+ * With relative atime, only update atime if the
+ * previous atime is earlier than either the ctime or
+ * mtime.
+ */
+static int relatime_need_update(struct inode *inode, struct timespec now)
+{
+ /*
+ * Is mtime younger than atime? If yes, update atime:
+ */
+ if (timespec_compare(&inode->i_mtime, &inode->i_atime) >= 0)
+ return 1;
+ /*
+ * Is ctime younger than atime? If yes, update atime:
+ */
+ if (timespec_compare(&inode->i_ctime, &inode->i_atime) >= 0)
+ return 1;
+
+ /*
+ * Is the previous atime value older than a day? If yes,
+ * update atime:
+ */
+ if ((long)(now.tv_sec - inode->i_atime.tv_sec) >= 24*60*60)
+ return 1;
+ /*
+ * Good, we can skip the atime update:
+ */
+ return 0;
+}
+
/**
* touch_atime - update the access time
* @mnt: mount the inode is accessed on
@@ -1191,22 +1221,14 @@ void touch_atime(struct vfsmount *mnt, s
return;
if ((mnt->mnt_flags & MNT_NODIRATIME) && S_ISDIR(inode->i_mode))
return;
-
- if (mnt->mnt_flags & MNT_RELATIME) {
- /*
- * With relative atime, only update atime if the
- * previous atime is earlier than either the ctime or
- * mtime.
- */
- if (timespec_compare(&inode->i_mtime,
- &inode->i_atime) < 0 &&
- timespec_compare(&inode->i_ctime,
- &inode->i_atime) < 0)
+ }
+ now = current_fs_time(inode->i_sb);
+ if (mnt) {
+ if (mnt->mnt_flags & MNT_RELATIME)
+ if (!relatime_need_update(inode, now))
return;
- }
}

- now = current_fs_time(inode->i_sb);
if (timespec_equal(&inode->i_atime, &now))
return;

Index: linux/fs/namespace.c
===================================================================
--- linux.orig/fs/namespace.c
+++ linux/fs/namespace.c
@@ -1107,6 +1107,8 @@ int do_add_mount(struct vfsmount *newmnt
goto unlock;

newmnt->mnt_flags = mnt_flags;
+ WARN_ON_ONCE(newmnt->mnt_flags & MNT_RELATIME);
+
if ((err = graft_tree(newmnt, nd)))
goto unlock;

@@ -1362,6 +1364,60 @@ int copy_mount_options(const void __user
}

/*
+ * Allow users to disable (or enable) atime updates via a .config
+ * option or via the boot line, or via /proc/sys/fs/mount_with_relatime:
+ */
+int mount_with_relatime __read_mostly =
+#ifdef CONFIG_DEFAULT_RELATIME
+1
+#else
+0
+#endif
+;
+
+/*
+ * The "norelatime=", "atime=", "norelatime" and "relatime" boot parameters:
+ */
+static int toggle_relatime_updates(int val)
+{
+ mount_with_relatime = val;
+
+ printk("Relative atime updates are: %s\n", val ? "on" : "off");
+
+ return 1;
+}
+
+static int __init set_relatime_setup(char *str)
+{
+ int val;
+
+ get_option(&str, &val);
+ return toggle_relatime_updates(val);
+}
+__setup("relatime=", set_relatime_setup);
+
+static int __init set_norelatime_setup(char *str)
+{
+ int val;
+
+ get_option(&str, &val);
+ return toggle_relatime_updates(!val);
+}
+__setup("norelatime=", set_norelatime_setup);
+
+static int __init set_relatime(char *str)
+{
+ return toggle_relatime_updates(1);
+}
+__setup("relatime", set_relatime);
+
+static int __init set_norelatime(char *str)
+{
+ return toggle_relatime_updates(0);
+}
+__setup("norelatime", set_norelatime);
+
+/*
* Flags is a 32-bit value that allows up to 31 non-fs dependent flags to
* be given to the mount() call (ie: read-only, no-dev, no-suid etc).
*
@@ -1409,6 +1465,11 @@ long do_mount(char *dev_name, char *dir_
mnt_flags |= MNT_NODIRATIME;
if (flags & MS_RELATIME)
mnt_flags |= MNT_RELATIME;
+ else if (mount_with_relatime &&
+ !(flags & (MNT_NOATIME | MNT_NODIRATIME))) {
+ mnt_flags |= MNT_RELATIME;
+ flags |= MS_RELATIME;
+ }

flags &= ~(MS_NOSUID | MS_NOEXEC | MS_NODEV | MS_ACTIVE |
MS_NOATIME | MS_NODIRATIME | MS_RELATIME);
Index: linux/include/linux/mount.h
===================================================================
--- linux.orig/include/linux/mount.h
+++ linux/include/linux/mount.h
@@ -103,5 +103,7 @@ extern void shrink_submounts(struct vfsm
extern spinlock_t vfsmount_lock;
extern dev_t name_to_dev_t(char *name);

+extern int mount_with_relatime;
+
#endif
#endif /* _LINUX_MOUNT_H */
Index: linux/kernel/sysctl.c
===================================================================
--- linux.orig/kernel/sysctl.c
+++ linux/kernel/sysctl.c
@@ -30,6 +30,7 @@
#include <linux/capability.h>
#include <linux/smp_lock.h>
#include <linux/fs.h>
+#include <linux/mount.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/kobject.h>
@@ -1206,6 +1207,14 @@ static ctl_table fs_table[] = {
.mode = 0644,
.proc_handler = &proc_dointvec,
},
+ {
+ .ctl_name = CTL_UNNUMBERED,
+ .procname = "mount_with_relatime",
+ .data = &mount_with_relatime,
+ .maxlen = sizeof(int),
+ .mode = 0644,
+ .proc_handler = &proc_dointvec,
+ },
#if defined(CONFIG_BINFMT_MISC) || defined(CONFIG_BINFMT_MISC_MODULE)
{
.ctl_name = CTL_UNNUMBERED,