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SubjectRe: [PATCH][RF C/T/D] Unmapped page cache control - via boot parameter
On 03/17/2010 10:49 AM, Christoph Hellwig wrote:
> On Tue, Mar 16, 2010 at 01:08:28PM +0200, Avi Kivity wrote:
>
>> If the batch size is larger than the virtio queue size, or if there are
>> no flushes at all, then yes the huge write cache gives more opportunity
>> for reordering. But we're already talking hundreds of requests here.
>>
> Yes. And rememember those don't have to come from the same host. Also
> remember that we rather limit execssive reodering of O_DIRECT requests
> in the I/O scheduler because they are "synchronous" type I/O while
> we don't do that for pagecache writeback.
>

Maybe we should relax that for kvm. Perhaps some of the problem comes
from the fact that we call io_submit() once per request.

> And we don't have unlimited virtio queue size, in fact it's quite
> limited.
>

That can be extended easily if it fixes the problem.

--
error compiling committee.c: too many arguments to function



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