[PATCH] md: increase the delay before marking metadata clean, and make it configurable

When a md array has been idle (no writes) for 20msecs it is marked as 'clean'.
 This delay turns out to be too short for some real workloads.  So increase it
to 200msec (the time to update the metadata should be a tiny fraction of that)
and make it sysfs-configurable.

Signed-off-by: Neil Brown <neilb@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

diff --git a/Documentation/md.txt b/Documentation/md.txt
index 03a13c462cf20ed8e09d85ead4b953cfad3b6218..b19978e035fca1f457ab8a39bca2fbb6191309a8 100644 (file)
--- a/Documentation/md.txt
+++ b/Documentation/md.txt
@@ -207,6 +207,15 @@ All md devices contain:
      available.  It will then appear at md/dev-XXX (depending on the
      name of the device) and further configuration is then possible.
 
+   safe_mode_delay
+     When an md array has seen no write requests for a certain period
+     of time, it will be marked as 'clean'.  When another write
+     request arrive, the array is marked as 'dirty' before the write
+     commenses.  This is known as 'safe_mode'.
+     The 'certain period' is controlled by this file which stores the
+     period as a number of seconds.  The default is 200msec (0.200).
+     Writing a value of 0 disables safemode.
+
    sync_speed_min
    sync_speed_max
      This are similar to /proc/sys/dev/raid/speed_limit_{min,max}

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 30a93d64921e618d64cc844f48f50e01ed44a8ab..ad576ad2ca763b7c973c1b9ffae91f6fb6537c24 100644 (file)
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -44,6 +44,7 @@
 #include <linux/suspend.h>
 #include <linux/poll.h>
 #include <linux/mutex.h>
+#include <linux/ctype.h>
 
 #include <linux/init.h>
 
@@ -1977,6 +1978,54 @@ static void analyze_sbs(mddev_t * mddev)
 
 }
 
+static ssize_t
+safe_delay_show(mddev_t *mddev, char *page)
+{
+       int msec = (mddev->safemode_delay*1000)/HZ;
+       return sprintf(page, "%d.%03d\n", msec/1000, msec%1000);
+}
+static ssize_t
+safe_delay_store(mddev_t *mddev, const char *cbuf, size_t len)
+{
+       int scale=1;
+       int dot=0;
+       int i;
+       unsigned long msec;
+       char buf[30];
+       char *e;
+       /* remove a period, and count digits after it */
+       if (len >= sizeof(buf))
+               return -EINVAL;
+       strlcpy(buf, cbuf, len);
+       buf[len] = 0;
+       for (i=0; i<len; i++) {
+               if (dot) {
+                       if (isdigit(buf[i])) {
+                               buf[i-1] = buf[i];
+                               scale *= 10;
+                       }
+                       buf[i] = 0;
+               } else if (buf[i] == '.') {
+                       dot=1;
+                       buf[i] = 0;
+               }
+       }
+       msec = simple_strtoul(buf, &e, 10);
+       if (e == buf || (*e && *e != '\n'))
+               return -EINVAL;
+       msec = (msec * 1000) / scale;
+       if (msec == 0)
+               mddev->safemode_delay = 0;
+       else {
+               mddev->safemode_delay = (msec*HZ)/1000;
+               if (mddev->safemode_delay == 0)
+                       mddev->safemode_delay = 1;
+       }
+       return len;
+}
+static struct md_sysfs_entry md_safe_delay =
+__ATTR(safe_mode_delay, 0644,safe_delay_show, safe_delay_store);
+
 static ssize_t
 level_show(mddev_t *mddev, char *page)
 {
@@ -2433,6 +2482,7 @@ static struct attribute *md_default_attrs[] = {
        &md_size.attr,
        &md_metadata.attr,
        &md_new_device.attr,
+       &md_safe_delay.attr,
        NULL,
 };
 
@@ -2708,7 +2758,7 @@ static int do_md_run(mddev_t * mddev)
        mddev->safemode = 0;
        mddev->safemode_timer.function = md_safemode_timeout;
        mddev->safemode_timer.data = (unsigned long) mddev;
-       mddev->safemode_delay = (20 * HZ)/1000 +1; /* 20 msec delay */
+       mddev->safemode_delay = (200 * HZ)/1000 +1; /* 200 msec delay */
        mddev->in_sync = 1;
 
        ITERATE_RDEV(mddev,rdev,tmp)
@@ -4594,7 +4644,7 @@ void md_write_end(mddev_t *mddev)
        if (atomic_dec_and_test(&mddev->writes_pending)) {
                if (mddev->safemode == 2)
                        md_wakeup_thread(mddev->thread);
-               else
+               else if (mddev->safemode_delay)
                        mod_timer(&mddev->safemode_timer, jiffies + mddev->safemode_delay);
        }
 }