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Commit 696fcd53 authored by Paul Clements's avatar Paul Clements Committed by NeilBrown
Browse files

md: expose max value of behind writes counter 



Keep track of the maximum number of concurrent write-behind requests
for an md array and exposed this number in sysfs at
   md/bitmap/max_backlog_used

Writing any value to this file will clear it.

This allows userspace to be involved in tuning bitmap/backlog.

Signed-off-by: default avatarPaul Clements <paul.clements@steeleye.com>
Signed-off-by: default avatarNeilBrown <neilb@suse.de>
parent ee8b81b0

drivers/md/bitmap.c

+28 −1
Original line number Diff line number Diff line
@@ -1292,9 +1292,14 @@ int bitmap_startwrite(struct bitmap *bitmap, sector_t offset, unsigned long sect 
	if (!bitmap) return 0;



	if (behind) {

		int bw;

		atomic_inc(&bitmap->behind_writes);

		bw = atomic_read(&bitmap->behind_writes);

		if (bw > bitmap->behind_writes_used)

			bitmap->behind_writes_used = bw;



		PRINTK(KERN_DEBUG "inc write-behind count %d/%d\n",

		  atomic_read(&bitmap->behind_writes), bitmap->max_write_behind);

		       bw, bitmap->max_write_behind);

	}



	while (sectors) {
@@ -2006,6 +2011,27 @@ static ssize_t can_clear_store(mddev_t *mddev, const char *buf, size_t len) 
static struct md_sysfs_entry bitmap_can_clear =

__ATTR(can_clear, S_IRUGO|S_IWUSR, can_clear_show, can_clear_store);



static ssize_t

behind_writes_used_show(mddev_t *mddev, char *page)

{

	if (mddev->bitmap == NULL)

		return sprintf(page, "0\n");

	return sprintf(page, "%lu\n",

		       mddev->bitmap->behind_writes_used);

}



static ssize_t

behind_writes_used_reset(mddev_t *mddev, const char *buf, size_t len)

{

	if (mddev->bitmap)

		mddev->bitmap->behind_writes_used = 0;

	return len;

}



static struct md_sysfs_entry max_backlog_used =

__ATTR(max_backlog_used, S_IRUGO | S_IWUSR,

       behind_writes_used_show, behind_writes_used_reset);



static struct attribute *md_bitmap_attrs[] = {

	&bitmap_location.attr,

	&bitmap_timeout.attr,
@@ -2013,6 +2039,7 @@ static struct attribute *md_bitmap_attrs[] = { 
	&bitmap_chunksize.attr,

	&bitmap_metadata.attr,

	&bitmap_can_clear.attr,

	&max_backlog_used.attr,

	NULL

};

struct attribute_group md_bitmap_group = {

drivers/md/bitmap.h

+1 −0
Original line number Diff line number Diff line
@@ -227,6 +227,7 @@ struct bitmap { 
	int allclean;



	atomic_t behind_writes;

	unsigned long behind_writes_used; /* highest actual value at runtime */



	/*

	 * the bitmap daemon - periodically wakes up and sweeps the bitmap