On 2020/5/28 22:28, Song Liu wrote:

On Thu, May 28, 2020 at 7:10 AM Song Liu [off-list ref] wrote:

quoted

On Wed, May 27, 2020 at 6:20 AM Yufen Yu [off-list ref] wrote:

quoted

Hi, all

  For now, STRIPE_SIZE is equal to the value of PAGE_SIZE. That means, RAID5 will
  issus echo bio to disk at least 64KB when PAGE_SIZE is 64KB in arm64. However,
  filesystem usually issue bio in the unit of 4KB. Then, RAID5 will waste resource
  of disk bandwidth.

Thanks for the patch set.

Since this is a big change, I am planning to process this set after
upcoming merge window.
Please let me know if you need it urgently.

I agree with your plan.

I haven't thought about this in detail yet: how about compatibility?
Say we create an
array with STRIPE_SIZE of 4kB, does it work well after we upgrade kernel to have
STRIPE_SIZE of 8kB?

Each time upgrade kernel, we need to reboot system to make it effective.
And, system will allocate new stripe_head and buffers base on the new STRIPE_SIZE.
Then everything will be ok and go on running.

STRIPE_SIZE decides each io size issued to array disk and its buffers size in
stripe_head. But each time restart system, we will allocate new buffer and
stripe_head based on the new STRIPE_SIZE. It is no matter what the value before.
So, I think changing STRIPE_SIZE is not problem for upgrade kernel.

Thanks,
Yufen