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SubjectRe: [PATCH][RF C/T/D] Unmapped page cache control - via boot parameter
On Wed, Mar 17, 2010 at 06:22:29PM +0200, Avi Kivity wrote:
> They should be reorderable. Otherwise host filesystems on several
> volumes would suffer the same problems.

They are reordable, just not as extremly as the the page cache.
Remember that the request queue really is just a relatively small queue
of outstanding I/O, and that is absolutely intentional. Large scale
_caching_ is done by the VM in the pagecache, with all the usual aging,
pressure, etc algorithms applied to it. The block devices have a
relatively small fixed size request queue associated with it to
facilitate request merging and limited reordering and having fully
set up I/O requests for the device.



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