Re: Questions answered by Neil Brown

"Peter T. Breuer" wrote:

"A month of sundays ago Neil Brown wrote:"

quoted

On Monday February 24, Paul.Clements@SteelEye.com wrote:

So it might be enough to chain all the mirror bh's through
bh->b_this_page.

That's an interesting idea. I looked through the code and I have some
questions:

What if the user is waiting on a page and not a buffer (not sure if that
can/will happen). In that case, we'd be artificially causing him to wait
when it wasn't necessary. Suppose all the I/O for a page really was
complete, but we kept the user waiting until all the mirror I/Os
(including ones to backup devices) for that page had completed. 

Another thing I'm not sure about is whether it's safe for raid1 to
modify the b_this_page field (for a buffer that was passed in from
above)...we'd at least have to insert our values into the existing list.
Is it safe to modify the list without any locks held?

 

I believe that currently this field is just set to "1" in
raid1_make_request().

Yeah, I sure wish I knew who did that and why. I wonder if someone had a
clever plan to use that field at some point, but never got around to it.
Setting that field to something besides a real address sure does seem
odd...and I can't see that it's ever used anywhere.

--
Paul