Re: [PATCH] btrfs_progs: mkfs: match devid order to the stripe index

[Anand Jain <anand.jain@oracle.com>]

On 28/6/19 10:44 AM, Qu Wenruo wrote:
> 
> 
> On 2019/6/28 上午10:26, Anand Jain wrote:
>> At the time mkfs.btrfs the device id and stripe index gets reversed as
>> shown in [1]. This patch helps to keep them in order at the time of
>> mkfs.btrfs. And makes it easier to debug.
>>
>> Before:
>> Stripe 0 is on devid 2; Stipe 1 is on devid 1;
>>
>> ./mkfs.btrfs -fq -draid1 -mraid1 /dev/sdb /dev/sdc && btrfs in dump-tree -d /dev/sdb | grep -A 10000 "chunk tree" | grep -B 10000 "device tree" | grep -A 13  "FIRST_CHUNK_TREE CHUNK_ITEM"
>> 	item 2 key (FIRST_CHUNK_TREE CHUNK_ITEM 22020096) itemoff 15975 itemsize 112
>> 		length 8388608 owner 2 stripe_len 65536 type SYSTEM|RAID1
>> 		io_align 65536 io_width 65536 sector_size 4096
>> 		num_stripes 2 sub_stripes 0
>> 			stripe 0 devid 2 offset 1048576
>> 			dev_uuid d9fe51c4-6e79-446d-87ee-5be3184798cd
>> 			stripe 1 devid 1 offset 22020096
>> 			dev_uuid 16f626ca-1a54-469b-ac7e-25623af884ab
>> 	item 3 key (FIRST_CHUNK_TREE CHUNK_ITEM 30408704) itemoff 15863 itemsize 112
>> 		length 268435456 owner 2 stripe_len 65536 type METADATA|RAID1
>> 		io_align 65536 io_width 65536 sector_size 4096
>> 		num_stripes 2 sub_stripes 0
>> 			stripe 0 devid 2 offset 9437184
>> 			dev_uuid d9fe51c4-6e79-446d-87ee-5be3184798cd
>> 			stripe 1 devid 1 offset 30408704
>> 			dev_uuid 16f626ca-1a54-469b-ac7e-25623af884ab
>> 	item 4 key (FIRST_CHUNK_TREE CHUNK_ITEM 298844160) itemoff 15751 itemsize 112
>> 		length 314572800 owner 2 stripe_len 65536 type DATA|RAID1
>> 		io_align 65536 io_width 65536 sector_size 4096
>> 		num_stripes 2 sub_stripes 0
>> 			stripe 0 devid 2 offset 277872640
>> 			dev_uuid d9fe51c4-6e79-446d-87ee-5be3184798cd
>> 			stripe 1 devid 1 offset 298844160
>> 			dev_uuid 16f626ca-1a54-469b-ac7e-25623af884ab
>>
>> After:
>> Stripe 0 is on devid 1; Stripe 1 is on devid 2
>>
>> ./mkfs.btrfs -fq -draid1 -mraid1 /dev/sdb /dev/sdc && btrfs in dump-tree -d /dev/sdb | grep -A 10000 "chunk tree" | grep -B 10000 "device tree" | grep -A 13  "FIRST_CHUNK_TREE CHUNK_ITEM"
>> /dev/sdb: 8 bytes were erased at offset 0x00010040 (btrfs): 5f 42 48 52 66 53 5f 4d
>> /dev/sdc: 8 bytes were erased at offset 0x00010040 (btrfs): 5f 42 48 52 66 53 5f 4d
>> 	item 2 key (FIRST_CHUNK_TREE CHUNK_ITEM 22020096) itemoff 15975 itemsize 112
>> 		length 8388608 owner 2 stripe_len 65536 type SYSTEM|RAID1
>> 		io_align 65536 io_width 65536 sector_size 4096
>> 		num_stripes 2 sub_stripes 0
>> 			stripe 0 devid 1 offset 22020096
>> 			dev_uuid 6abc88fa-f42e-4f0c-9bc3-2225735e51d1
>> 			stripe 1 devid 2 offset 1048576
>> 			dev_uuid 73746d27-13a6-4d58-ac6b-48c90c31d94d
>> 	item 3 key (FIRST_CHUNK_TREE CHUNK_ITEM 30408704) itemoff 15863 itemsize 112
>> 		length 268435456 owner 2 stripe_len 65536 type METADATA|RAID1
>> 		io_align 65536 io_width 65536 sector_size 4096
>> 		num_stripes 2 sub_stripes 0
>> 			stripe 0 devid 1 offset 30408704
>> 			dev_uuid 6abc88fa-f42e-4f0c-9bc3-2225735e51d1
>> 			stripe 1 devid 2 offset 9437184
>> 			dev_uuid 73746d27-13a6-4d58-ac6b-48c90c31d94d
>> 	item 4 key (FIRST_CHUNK_TREE CHUNK_ITEM 298844160) itemoff 15751 itemsize 112
>> 		length 314572800 owner 2 stripe_len 65536 type DATA|RAID1
>> 		io_align 65536 io_width 65536 sector_size 4096
>> 		num_stripes 2 sub_stripes 0
>> 			stripe 0 devid 1 offset 298844160
>> 			dev_uuid 6abc88fa-f42e-4f0c-9bc3-2225735e51d1
>> 			stripe 1 devid 2 offset 277872640
>> 			dev_uuid 73746d27-13a6-4d58-ac6b-48c90c31d94d
>>
>> Signed-off-by: Anand Jain <anand.jain@oracle.com>
> 
> Reviewed-by: Qu Wenruo <wqu@suse.com>
> 
> But please also check the comment inlined below.
>> ---
>>   volumes.c | 4 ++--
>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/volumes.c b/volumes.c
>> index 79d1d6a07fb7..8c8b17e814b8 100644
>> --- a/volumes.c
>> +++ b/volumes.c
>> @@ -1109,7 +1109,7 @@ again:
>>   			return ret;
>>   		cur = cur->next;
>>   		if (avail >= min_free) {
>> -			list_move_tail(&device->dev_list, &private_devs);
>> +			list_move(&device->dev_list, &private_devs);
> 
> This is OK since current btrfs-progs chunk allocator doesn't follow the
> kernel behavior by sorting devices with its unallocated space.
> So it's completely devid based.
> 
> But please keep in mind that, if we're going to unify the chunk
> allocator behavior of kernel and btrfs-progs, the behavior will change.
> 
> As the initial temporary chunk is always allocated on devid 1, reducing
> its unallocated space thus reducing its priority in chunk allocator, and
> making the devid sequence more unreliable.

  Right. For the debug here, I have an experimental code which disables
  the unallocated space sort in the kernel. I don't have a strong reason
  to disable the sort in the kernel so didn't send the patch.

Thanks, Anand

> Thanks,
> Qu
> 
>>   			index++;
>>   			if (type & BTRFS_BLOCK_GROUP_DUP)
>>   				index++;
>> @@ -1166,7 +1166,7 @@ again:
>>   		/* loop over this device again if we're doing a dup group */
>>   		if (!(type & BTRFS_BLOCK_GROUP_DUP) ||
>>   		    (index == num_stripes - 1))
>> -			list_move_tail(&device->dev_list, dev_list);
>> +			list_move(&device->dev_list, dev_list);
>>   
>>   		ret = btrfs_alloc_dev_extent(trans, device, key.offset,
>>   			     calc_size, &dev_offset);
>>
>