Re: [PATCH 1/2] bcache: Remove redundant set_capacity

[wangyijing <wangyijing@huawei.com>]

>>> It probably is a duplicate set_capacity, but has anyone tested bringing on 
>>> a writeback volume, and late-attaching the cache volume with this patch 
>>> applied?
>>>
>>> Otherwise stated, is it possible to get the backing device attached 
>>> without setting the capacity?
>>
>> Hi Eric, I tested this case in following steps, the result is fine, the capability is setted.
>>
>> [root@38 sys]# make-bcache -B /dev/nvme1n1
>> UUID:			6758bd42-c226-4de9-a6d5-fb003af63f9f
>> Set UUID:		2661eadd-79b4-4c56-a2fb-9f8b505aa9fd
>> version:		1
>> block_size:		1
>> data_offset:		16
>> [root@38 sys]# ls /dev/bcache
>> bcache/  bcache0
>> [root@38 sys]# fdisk -l
>> Disk /dev/nvme1n1: 1.8 TiB, 2000398934016 bytes, 3907029168 sectors
>> Units: sectors of 1 * 512 = 512 bytes
>> Sector size (logical/physical): 512 bytes / 512 bytes
>> I/O size (minimum/optimal): 512 bytes / 512 bytes
>> ....
>> Disk /dev/bcache0: 1.8 TiB, 2000398925824 bytes, 3907029152 sectors
>> Units: sectors of 1 * 512 = 512 bytes
>> Sector size (logical/physical): 512 bytes / 512 bytes
>> I/O size (minimum/optimal): 512 bytes / 512 bytes
>> ....
>> [root@38 sys]# make-bcache -C /dev/ram0
>> UUID:			b64a4425-b9c1-4650-9cab-3856410c9566
>> Set UUID:		a0a31965-a89d-43b6-a5d6-968897abeb7a
>> version:		0
>> nbuckets:		1024
>> block_size:		1
>> bucket_size:		1024
>> nr_in_set:		1
>> nr_this_dev:		0
>> first_bucket:		1
>> [root@38 sys]# echo a0a31965-a89d-43b6-a5d6-968897abeb7a > /sys/block/bcache0/bcache/attach
>> [root@38 sys]# echo writeback > /sys/block/bcache0/bcache/cache_mode
>> [root@38 sys]# mount /dev/bcache0 /tmp
>> [root@38 sys]# cd /tmp/
>> [root@38 tmp]# fio ~/fio_write.sh
>> file1: (g=0): rw=randwrite, bs=4K-4K/4K-4K/4K-4K, ioengine=psync, iodepth=1
>> fio-2.2.8
>> Starting 1 thread
>> file1: Laying out IO file(s) (1 file(s) / 128MB)
>> Jobs: 1 (f=1): [w(1)] [0.0% done] [0KB/177.2MB/0KB /s] [0/45.4K/0 iops] [eta 05h:33m:13s]
>>
>> Thanks!
>> Yijing.
> 
> I want to make sure that the set_capacity call that happens on cache 
> attachment is not necessary when a backing device is attached without

Hi Eric, set_capacity() which removed in this patch is happened at cached_dev_init()
which is called when register a backing device, what do you mean "set_capacity call that happens on cache
> attachment" ?


> its dirty writeback cache since bcache0 is not presented until the cache 
> attaches in that case.

I found bcache0 device present once we do make-bcache -B /dev/nvme1n1. before attach the cache set.
So I missed something ?

> 
> Can you also unregister the volume, attach the backing device first, and 
> then the cache while the cache is dirty to make sure that the size is set 
> correctly?

When I unregister the cache device, I found all the dirty data has been flushed to
backing device, so how can I do the test the case as you point ?

Thanks!
Yijing.

> 
> --
> Eric Wheeler
> 
>>
>>>
>>> -Eric
>>>
>>>>  	dc->disk.disk->queue->backing_dev_info.ra_pages =
>>>>  		max(dc->disk.disk->queue->backing_dev_info.ra_pages,
>>>>  		    q->backing_dev_info.ra_pages);
>>>> -- 
>>>> 2.5.0
>>>>
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>>>
>>> .
>>>
>>
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