Re: 2.5.59-mm5

[Nick Piggin <piggin@cyberone.com.au>]

Giuliano Pochini wrote:

>>>An alternate approach might be to change the way the scheduler splits
>>>things. That is, rather than marking I/O read vs write and scheduling
>>>based on that, add a flag bit to mark them all sync vs async since
>>>that's the distinction we actually care about. The normal paths can
>>>all do read+sync and write+async, but you can now do things like
>>>marking your truncate writes sync and readahead async.
>>>
>
>>That will be worth investigating to see if the complexity is worth it.
>>I think from a disk point of view, we still want to split batches between
>>reads and writes. Could be wrong.
>>
>
>Yes, sync vs async is a better way to classify io requests than
>read vs write and it's more correct from OS point of view. IMHO
>it's not more complex then now. Just replace r/w with sy/as and
>it will work.
>
We probably wouldn't want to go that far as you obviously can
only merge reads with reads and writes with writes, a flag would
be fine. We have to get the basics working first though ;)