Re: [Qemu-devel] Re: [PATCH][v2] Align file accesses with cache=off (O_DIRECT)

[Anthony Liguori]

Andrea Arcangeli wrote:
> On Wed, May 21, 2008 at 08:18:01PM +0300, Avi Kivity wrote:
>   
> > Yes, that's the reason.  Here zerocopy is not the motivation; instead, we 
> > have host-cached pages that are used directly in the guest.  So we get both 
> > reduced memory footprint, and host caching.  O_DIRECT reduces the memory 
> > footprint but kills host caching.
> >     
>
> Sure. So MAP_SHARED+remap_file_pages should work just fine to achieve
> zerocopy I/O.
>   

MAP_SHARED cannot be done transparently to the guest, that's the 
motivating reason behind MAP_PRIVATE.

Regards,

Anthony Liguori