Xen currently allows granting a single frame to several domains, several times (to map or copy). Though the feature itself seems appealing, I wonder if there''s a real use case in any ports or PV aware applications (i.e. a page is mapped or copied by more than 2 domains). Is there? Except the condition outlined above, PGC_count_mask part of a page->count_info can be more than 1? Thanks, Mohammad _______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel
On 27/10/2011 22:16, "Mohammad Hedayati" <hedayati.mo@gmail.com> wrote:> Xen currently allows granting a single frame to several domains, > several times (to map or copy). Though the feature itself seems > appealing, I wonder if there''s a real use case in any ports or PV > aware applications (i.e. a page is mapped or copied by more than 2 > domains). Is there?It wouldn''t typically happen.> Except the condition outlined above, PGC_count_mask part of a > page->count_info can be more than 1?Yes. Go trace some count_info values in a running system. Most will be >1. -- Keir> Thanks, > Mohammad > > _______________________________________________ > Xen-devel mailing list > Xen-devel@lists.xensource.com > http://lists.xensource.com/xen-devel_______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel
Mohammad Hedayati
2011-Oct-28 08:57 UTC
Re: [Xen-devel] Allowing several mappings of a frame
On Fri, Oct 28, 2011 at 1:25 AM, Keir Fraser <keir.xen@gmail.com> wrote:> On 27/10/2011 22:16, "Mohammad Hedayati" <hedayati.mo@gmail.com> wrote: > >> Xen currently allows granting a single frame to several domains, >> several times (to map or copy). Though the feature itself seems >> appealing, I wonder if there''s a real use case in any ports or PV >> aware applications (i.e. a page is mapped or copied by more than 2 >> domains). Is there? > > It wouldn''t typically happen. > >> Except the condition outlined above, PGC_count_mask part of a >> page->count_info can be more than 1? > > Yes. Go trace some count_info values in a running system. Most will be >1. >I have traced the faulting pages in do_page_fault (where else?). The pages with more than one reference (PGC_count_mask & page->count_info) were flagged as PGT_lx_page_table or PGT_seg_desc_page (are the mappers dom_xen, dom_cow or dom_io?). Is there more than one reference for an ordinary pages?> -- Keir > >> Thanks, >> Mohammad >> >> _______________________________________________ >> Xen-devel mailing list >> Xen-devel@lists.xensource.com >> http://lists.xensource.com/xen-devel > > >How can I know, in addition to the owner, who has mapped a page? What does (PGT_count_mask & page->u.inuse.type_info) show? Why it is not the same as (PGC_count_mask & page->count_info)? Is there a documentation other than the comments in the code? Thanks, Mohammad _______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel