Hi Olaf --
I have two questions to ask you about xenpaging.
1) When guest os causes page_fault for the accessed page is paging_out
or paged,it will execute p2m_mem_paging_populate() .
and in p2m_mem_paging_populate() it will first check if the ring is full.
when I ran with domU suse11 4G memory and 8vcpus,I found there will
be a corruption in checking the ring.
For example,if 4vcpus are met with page faults when they access
different pages,and there is only four free-requests for the ring.
and then they call p2m_mem_paging_populate(),and execute
mem_event_check_ring(d) at the same time.All will find ring is not
full,and will fill the requests.It will cause the latter request to
cover the front request.
and I think there should a lock before the mem_event_check_ring(d)
,and normally it unlock after mem_event_put_request(d, &req).
You can review the attached doc of xenpaging_IO_ring.txt to see if my
opnion is right.
2)mem_sharing and xenpaging are shared with one IO ring for domU.In
the function of mem_sharing_alloc_page(),if alloc_domheap_page(d, 0)
returns NULL,then it will pause VCPU ,check if the ring is full,and
fill the request at last.
I think there is also a corruption of mem_event_check_ring(d) with it
in p2m_mem_paging_populate().We should assure
exclusively in reading the free_request and puting requests.
What''s more,although it hardly fails in alloc_domheap_page(d, 0) from
mem_sharing_alloc_page() ,it will fill the requests in IO ring.
But in xenpaging when handling the page_in requests,we have not
distinguished the requests with flag "MEM_EVENT_FLAG_VCPU_PAUSED" from
paging or sharing.It will cause if the request is from
mem_sharing_alloc_page(),it will
go to p2m_mem_paging_resume() at last,and the page''s p2mt is
p2m_ram_rw.I think this is wrong.Maybe we should add the req.type when
page in .
I''m so sorry to have a poor English.But I look forward to your early
reply.
Thank
you！
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On Thu, Sep 01, zhen shi wrote:> Hi Olaf -- > > I have two questions to ask you about xenpaging. > 1) When guest os causes page_fault for the accessed page is paging_out > or paged, it will execute p2m_mem_paging_populate(). and in > p2m_mem_paging_populate() it will first check if the ring is full. > when I ran with domU suse11 4G memory and 8vcpus, I found there will > be a corruption in checking the ring. > For example, if 4vcpus are met with page faults when they access > different pages, and there is only four free-requests for the ring. > and then they call p2m_mem_paging_populate(),and execute > mem_event_check_ring(d) at the same time.All will find ring is not > full,and will fill the requests. It will cause the latter request to > cover the front request. > and I think there should a lock before the mem_event_check_ring(d), > and normally it unlock after mem_event_put_request(d, &req). > You can review the attached doc of xenpaging_IO_ring.txt to see if my > opnion is right.Yes, you are right. I think mem_event_check_ring() should reserve a reference, and mem_event_put_request() should use that reference. mem_sharing_alloc_page() even has a comment that this should be done.> 2) mem_sharing and xenpaging are shared with one IO ring for domU. In > the function of mem_sharing_alloc_page(), if alloc_domheap_page(d, 0) > returns NULL, then it will pause VCPU, check if the ring is full, and > fill the request at last. > I think there is also a corruption of mem_event_check_ring(d) with it > in p2m_mem_paging_populate(). We should assure exclusively in reading > the free_request and puting requests. What''s more, although it hardly > fails in alloc_domheap_page(d, 0) from mem_sharing_alloc_page(), it > will fill the requests in IO ring. But in xenpaging when handling the > page_in requests, we have not distinguished the requests with flag > "MEM_EVENT_FLAG_VCPU_PAUSED" from paging or sharing. It will cause if > the request is from mem_sharing_alloc_page(), it will go to > p2m_mem_paging_resume() at last, and the page''s p2mt is p2m_ram_rw. I > think this is wrong. Maybe we should add the req.type when page in.Yes, get_request() in xenpaging should check the type before popping the request from the ring. Perhaps memsharing and xenpaging should use its own rings. Olaf _______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel
On Thu, Sep 01, Olaf Hering wrote:> On Thu, Sep 01, zhen shi wrote: > > > Hi Olaf -- > > > > I have two questions to ask you about xenpaging. > > 1) When guest os causes page_fault for the accessed page is paging_out > > or paged, it will execute p2m_mem_paging_populate(). and in > > p2m_mem_paging_populate() it will first check if the ring is full. > > when I ran with domU suse11 4G memory and 8vcpus, I found there will > > be a corruption in checking the ring. > > For example, if 4vcpus are met with page faults when they access > > different pages, and there is only four free-requests for the ring. > > and then they call p2m_mem_paging_populate(),and execute > > mem_event_check_ring(d) at the same time.All will find ring is not > > full,and will fill the requests. It will cause the latter request to > > cover the front request. > > and I think there should a lock before the mem_event_check_ring(d), > > and normally it unlock after mem_event_put_request(d, &req). > > You can review the attached doc of xenpaging_IO_ring.txt to see if my > > opnion is right. > > Yes, you are right. > I think mem_event_check_ring() should reserve a reference, and > mem_event_put_request() should use that reference. > mem_sharing_alloc_page() even has a comment that this should be done.Try this patch. It implements some ref counting. http://lists.xensource.com/archives/html/xen-devel/2011-09/msg00189.html Olaf _______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel