[Xen-devel] event channel in xenpaging

[zhen shi <bickys1986@xxxxxxxxx>]

Hi,Olaf,

I have some questions about event channel in Xenpaging to ask you.
1) In xenpaging it uses Inter-Domainain Commnication (IDC) between
dom0 and domU to build bidirectional connection,but I found there is
only an event channel notification from xen to dom0 when page faults
happens.It seems that xenpaging_resume_page()->xc_evtchn_notify()
doesn't make any difference.So why don't use vIRQ between dom0 and xen
instead of IDC between dom0 and domU?

2)In your latest patch,[PATCH 9 of 9] xenpaging: watch the domains
/xenpaging/num_pages xenstore value.I found some problems.
  a、In main(),you put the page_out process into while(1) and make the
following change.
     if ( interrupted )
    victims[i].gfn = INVALID_MFN;
    - else
    - evict_victim(paging, &victims[i], fd, i);
I think the" if ( interrupted )" should remove here.Because once
handling page_in requests,the related victims slot should clear,
then in evict_pages we can populate new page in this slot because in
evict_page() the condition as followings:
 /* Slot is allocated */
+ if ( victims[slot].gfn != INVALID_MFN )
+ continue;

b、In xenpaging_init (),when it goes to err,you add
"free(dom_path);free(watch_targetpages)" in PATCH 9,but I think we
should firstly judge if dom_path and watch_targetpages variables are
NULL.what's more ,if it initializes paging successfully，before "return
paging",we should free (dom_path),and free(watch_targetpages) in
xenpaging_teardown() lastly.
c、when initializing xenpaging fails,and goes to err,it returns NULL to
main() then exit main().
If it has already opened event channel,bind event notification,opened
connections to xen successfully when goes to err in
xenpaging_init()，how about dealing with these resources such as
xenpaging_teardown.

3)We have tested on Win7-32bit about 40vms to start xenpaging at the
same time.The vm is 1G 2VCPUS,and we page out 180M.Then we put 80-90%
memory pressure on each vm.About one hour later,there happens many
BSOD on vms.and most blue screen code is 0x... 7F or 0x...19. We guess
some special pages which systems need use to run may be paged out and
cause BSOD.and sometimes print out mmio information in messages.Do you
have any ideas about the BSOD on win7-32 bit vms?

I am looking forward to hearing from you. Thank you very much!  :)

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