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Commit 16f17b39 authored by NeilBrown's avatar NeilBrown Committed by Linus Torvalds
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[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: default avatarNeil Brown <neilb@suse.de>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 9443a1d1

Documentation/md.txt

+9 −0
Original line number Diff line number Diff line
@@ -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}

drivers/md/md.c

+52 −2
Original line number Diff line number Diff line
@@ -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);

	}

}