[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>

1 files changed, 52 insertions, 2 deletions

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 30a93d64921..ad576ad2ca7 100644
--- 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>
 
@@ -1978,6 +1979,54 @@ 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)
 {
 	struct mdk_personality *p = mddev->pers;
@@ -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);
 	}
 }