Set default bitmap-chunksize for internal bitmaps to at least 64Meg

A small bitmap-chunksize hurts performance without helping
resync speed much - particularly on internal bitmaps.

So set the default to at least 64Meg.

Signed-off-by: NeilBrown <neilb@suse.de>

mdadm.8

@@ -614,8 +614,8 @@ When using a file based bitmap, the default is to use the smallest
 size that is at-least 4 and requires no more than 2^21 chunks.
 When using an
 .B internal
-bitmap, the chunksize is automatically determined to make best use of
-available space.
+bitmap, the chunksize defaults to 64Meg, or larger if necessary to
+fit the bitmap into the available space.
 
 .TP
 .BR \-W ", " \-\-write\-mostly

super0.c

@@ -970,9 +970,14 @@ static int add_internal_bitmap0(struct supertype *st, int *chunkp,
 		min_chunk *= 2;
 		bits = (bits+1)/2;
 	}
-	if (chunk == UnSet)
+	if (chunk == UnSet) {
+		/* A chunk size less than a few Megabytes gives poor
+		 * performance without increasing resync noticeably
+		 */
 		chunk = min_chunk;
-	else if (chunk < min_chunk)
+		if (chunk < 64*1024*1024)
+			chunk = 64*1024*1024;
+	} else if (chunk < min_chunk)
 		return 0; /* chunk size too small */
 
 	sb->state |= (1<<MD_SB_BITMAP_PRESENT);

super1.c

@@ -1501,9 +1501,14 @@ add_internal_bitmap1(struct supertype *st,
 		min_chunk *= 2;
 		bits = (bits+1)/2;
 	}
-	if (chunk == UnSet)
+	if (chunk == UnSet) {
+		/* For practical purpose, 64Meg is a good
+		 * default chunk size for internal bitmaps.
+		 */
 		chunk = min_chunk;
-	else if (chunk < min_chunk)
+		if (chunk < 64*1024*1024)
+			chunk = 64*1024*1024;
+	} else if (chunk < min_chunk)
 		return 0; /* chunk size too small */
 	if (chunk == 0) /* rounding problem */
 		return 0;

tests/05r1-grow-internal

@@ -7,7 +7,7 @@ check wait
 testdev $md0 1 $mdsize1 1
 
 #mdadm -E $dev1
-mdadm --grow $md0 --bitmap=internal --delay=1 || { mdadm -X $dev2 ; exit 1; }
+mdadm --grow $md0 --bitmap=internal --bitmap-chunk=4 --delay=1 || { mdadm -X $dev2 ; exit 1; }
 dirty1=`mdadm -X $dev2 | sed -n -e 's/.*Bitmap.* \([0-9]*\) dirty.*/\1/p'`
 sleep 4
 dirty2=`mdadm -X $dev2 | sed -n -e 's/.*Bitmap.* \([0-9]*\) dirty.*/\1/p'`

tests/05r1-grow-internal-1

@@ -7,7 +7,7 @@ check wait
 testdev $md0 1 $mdsize1b 1
 
 #mdadm -E $dev1
-mdadm --grow $md0 --bitmap=internal --delay=1
+mdadm --grow $md0 --bitmap=internal --bitmap-chunk=4 --delay=1
 dirty1=`mdadm -X $dev2 | sed -n -e 's/.*Bitmap.* \([0-9]*\) dirty.*/\1/p'`
 sleep 4
 dirty2=`mdadm -X $dev2 | sed -n -e 's/.*Bitmap.* \([0-9]*\) dirty.*/\1/p'`

tests/05r1-internalbitmap

@@ -2,7 +2,7 @@
 # 
 # create a raid1 with an internal bitmap
 #
-mdadm --create -e0.90 --run $md0 --level=1 -n2 --delay=1  --bitmap internal $dev1 $dev2  
+mdadm --create -e0.90 --run $md0 --level=1 -n2 --delay=1  --bitmap internal --bitmap-chunk=4 $dev1 $dev2  
 check wait
 testdev $md0 1 $mdsize0 1
 mdadm -S $md0

tests/05r1-internalbitmap-v1a

@@ -2,7 +2,7 @@
 # 
 # create a raid1 with an internal bitmap
 #
-mdadm --create --run $md0 --metadata=1.0 --level=1 -n2 --delay=1  --bitmap internal $dev1 $dev2  
+mdadm --create --run $md0 --metadata=1.0 --level=1 -n2 --delay=1  --bitmap internal --bitmap-chunk=4 $dev1 $dev2  
 check wait
 check bitmap
 testdev $md0 1 $mdsize1b 1

tests/05r1-internalbitmap-v1b

@@ -2,7 +2,7 @@
 # 
 # create a raid1 with an internal bitmap
 #
-mdadm --create --run $md0 --metadata=1.1 --level=1 -n2 --delay=1  --bitmap internal $dev1 $dev2  
+mdadm --create --run $md0 --metadata=1.1 --level=1 -n2 --delay=1  --bitmap internal --bitmap-chunk=4 $dev1 $dev2  
 check wait
 check bitmap
 testdev $md0 1 $mdsize11 1

tests/05r1-internalbitmap-v1c

@@ -2,7 +2,7 @@
 # 
 # create a raid1 with an internal bitmap
 #
-mdadm --create --run $md0 --metadata=1.2 --level=1 -n2 --delay=1  --bitmap internal $dev1 $dev2  
+mdadm --create --run $md0 --metadata=1.2 --level=1 -n2 --delay=1  --bitmap internal --bitmap-chunk 4 $dev1 $dev2  
 check wait
 check bitmap
 testdev $md0 1 $mdsize12 1

tests/05r1-re-add

@@ -5,7 +5,7 @@
 # Then do some IO first.  Resync should still be very fast
 #
 
-mdadm -CR $md0 -l1 -n2 -binternal -d1 $dev1 $dev2
+mdadm -CR $md0 -l1 -n2 -binternal --bitmap-chunk=4 -d1 $dev1 $dev2
 check resync
 check wait
 testdev $md0 1 $mdsize1 1

tests/05r5-internalbitmap

@@ -2,7 +2,7 @@
 #
 # create a raid1 with an internal bitmap
 #
-mdadm --create --run $md0 --level=5 -n3 --delay=1  --bitmap internal $dev1 $dev2 $dev3
+mdadm --create --run $md0 --level=5 -n3 --delay=1  --bitmap internal --bitmap-chunk=4 $dev1 $dev2 $dev3
 check wait
 testdev $md0 2 $mdsize1 512
 mdadm -S $md0

tests/06update-uuid

@@ -57,7 +57,7 @@ fi
 mdadm -S /dev/md0
 
 # Internal bitmaps too.
-mdadm -CR --assume-clean  -b internal $md0 -l5 -n3 $dev0 $dev1 $dev2
+mdadm -CR --assume-clean  -b internal --bitmap-chunk 4 $md0 -l5 -n3 $dev0 $dev1 $dev2
 mdadm -S /dev/md0
 mdadm -A /dev/md0 --update=uuid --uuid=0123456789abcdef:fedcba9876543210 $dev0 $dev1 $dev2
 no_errors
@@ -69,7 +69,7 @@ mdadm -X $dev0 | grep -s > /dev/null 01234567:89abcdef:fedcba98:76543210 || {
 }
 mdadm -S /dev/md0
 
-mdadm -CR --assume-clean -e1.2 -b internal $md0 -l5 -n3 $dev0 $dev1 $dev2
+mdadm -CR --assume-clean -e1.2 -b internal --bitmap-chunk=4 $md0 -l5 -n3 $dev0 $dev1 $dev2
 mdadm -S /dev/md0
 mdadm -A /dev/md0 --update=uuid --uuid=0123456789abcdef:fedcba9876543210 $dev0 $dev1 $dev2
 no_errors

tests/06wrmostly

@@ -8,7 +8,7 @@ testdev $md0 1 $mdsize1 1
 
 mdadm -S $md0
 
-mdadm -CR $md0 -l1 -n3 --write-behind --bitmap=internal $dev0 $dev1 --write-mostly $dev2
+mdadm -CR $md0 -l1 -n3 --write-behind --bitmap=internal --bitmap-chunk=4 $dev0 $dev1 --write-mostly $dev2
 testdev $md0 1 $mdsize1 1
 mdadm -S $md0