Re: Raid10 and page cache

[NeilBrown <neilb@suse.de>]

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On Tue, 6 Dec 2011 20:04:33 -0800 Yucong Sun (叶雨飞) <sunyucong@gmail.com>
wrote:

> The problem with using page-flush as a write cache here is that write
> to MD don't go through IO scheduler, which is a very big problem,
> because when flush thread decide to write to MD,  it's impossible to
> control the write speed, or prioritize them with read, every requests
> basically is a fifo,  and when flush size is big, no read can be
> served.
> 

I'm not sure I understand....

Requests don't go through an IO scheduler before they hit md, but they do
after md sends them on down, so they can be re-ordered there.

There was a bug where raid10 would allow an arbitrary number of writes to
queue up so that flushing code didn't know when to stop.

This was fixed by 
   commit 34db0cd60f8a1f4ab73d118a8be3797c20388223

nearly 2 months ago :-)

NeilBrown


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