Re: [RFC] Live resize of backing device

[mingzhe <mingzhe.zou@easystack.cn>]

在 2023/2/19 17:39, Coly Li 写道:
> 
> 
>> 2023年1月27日 20:44，Andrea Tomassetti <andrea.tomassetti-opensource@devo.com> 写道：
>>
>>  From 83f490ec8e81c840bdaf69e66021d661751975f2 Mon Sep 17 00:00:00 2001
>> From: Andrea Tomassetti <andrea.tomassetti-opensource@devo.com>
>> Date: Thu, 8 Sep 2022 09:47:55 +0200
>> Subject: [PATCH v2] bcache: Add support for live resize of backing devices
>>
>> Signed-off-by: Andrea Tomassetti <andrea.tomassetti-opensource@devo.com>
> 
> Hi Andrea,
> 
> I am fine with this patch and added it in my test queue now. Do you have an updated version, (e.g. more coding refine or adding commit log), then I can update my local version.
> 
> BTW, it could be better if the patch will be sent out as a separated email.
> 
> Thanks.
> 
> Coly Li
> 
Hi, Coly

I posted some patchsets about online resize.

-[PATCH v5 1/3] bcache: add dirty_data in struct bcache_device
-[PATCH v5 2/3] bcache: allocate stripe memory when 
partial_stripes_expensive is true
-[PATCH v5 3/3] bcache: support online resizing of cached_dev

There are some differences:
1. Create /sys/block/bcache0/bcache/size in sysfs to trigger resize
2. Allocate stripe memory only if partial_stripes_expensive is true
3. Simplify bcache_dev_sectors_dirty()

Since the bcache superblock uses some sectors, the actual space of the 
bcache device is smaller than the backing. In order to provide a bcache 
device with a user-specified size, we need to create a backing device 
with a larger space, and then resize bcache. So resize can specify the 
size is very necessary.




> 
> 
>> ---
>> Hi Coly,
>> this is the second version of the patch. As you correctly pointed out,
>> I implemented roll-back functionalities in case of error.
>> I'm testing this funcionality using QEMU/KVM vm via libvirt.
>> Here the steps:
>>   1. make-bcache --writeback -B /dev/vdb -C /dev/vdc
>>   2. mkfs.xfs /dev/bcache0
>>   3. mount /dev/bcache0 /mnt
>>   3. dd if=/dev/random of=/mnt/random0 bs=1M count=1000
>>   4. md5sum /mnt/random0 | tee /mnt/random0.md5
>>   5. [HOST] virsh blockresize <vm-name> --path <disk-path> --size <new-size>
>>   6. xfs_growfs /dev/bcache0
>>   6. Repeat steps 3 and 4 with a different file name (e.g. random1.md5)
>>   7. umount/reboot/remount and check that the md5 hashes are correct with
>>         md5sum -c /mnt/random?.md5
>>
>> drivers/md/bcache/super.c | 84 ++++++++++++++++++++++++++++++++++++++-
>> 1 file changed, 83 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
>> index ba3909bb6bea..1435a3f605f8 100644
>> --- a/drivers/md/bcache/super.c
>> +++ b/drivers/md/bcache/super.c
>>>
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