From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Chen, Tiejun" <tiejun.chen@intel.com>
Subject: Re: [PATCH] xen/domctl: lower loglevel of
 XEN_DOMCTL_memory_mapping
Date: Thu, 10 Sep 2015 13:28:32 +0800
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To: Jan Beulich <JBeulich@suse.com>, Malcolm Crossley <malcolm.crossley@citrix.com>
Cc: Keir Fraser <keir@xen.org>, Ian Campbell <ian.campbell@citrix.com>, IanJackson <ian.jackson@eu.citrix.com>, Tim Deegan <tim@xen.org>, xen-devel@lists.xen.org
List-Id: xen-devel@lists.xenproject.org

>> If the 64 limit was arbitrary then I would suggest increasing it to at least
>> 1024 so that
>> at least 4M of BAR can be mapped in one go and it reduces the overhead by a
>> factor of 16.
>
> 1024 may be a little much, but 256 is certainly a possibility, plus
> Konrad's suggestion to allow this limit to be controlled via command
> line option.

Are you guys talking this way?

diff --git a/xen/arch/x86/setup.c b/xen/arch/x86/setup.c
index 3946e4c..a9671bb 100644
--- a/xen/arch/x86/setup.c
+++ b/xen/arch/x86/setup.c
@@ -88,6 +88,10 @@ boolean_param("noapic", skip_ioapic_setup);
  s8 __read_mostly xen_cpuidle = -1;
  boolean_param("cpuidle", xen_cpuidle);

+/* once_mapping_mfns: memory mapping mfn bumbers once. */
+unsigned int xen_once_mapping_mfns;
+integer_param("once_mapping_mfns", xen_once_mapping_mfns);
+
  #ifndef NDEBUG
  unsigned long __initdata highmem_start;
  size_param("highmem-start", highmem_start);
diff --git a/xen/common/domctl.c b/xen/common/domctl.c
index 3bf39f1..82c85e3 100644
--- a/xen/common/domctl.c
+++ b/xen/common/domctl.c
@@ -33,6 +33,8 @@
  #include <public/domctl.h>
  #include <xsm/xsm.h>

+extern unsigned int xen_once_mapping_mfns;
+
  static DEFINE_SPINLOCK(domctl_lock);
  DEFINE_SPINLOCK(vcpu_alloc_lock);

@@ -1035,7 +1037,7 @@ long 
do_domctl(XEN_GUEST_HANDLE_PARAM(xen_domctl_t) u_domctl)

          ret = -E2BIG;
          /* Must break hypercall up as this could take a while. */
-        if ( nr_mfns > 64 )
+        if ( nr_mfns > xen_once_mapping_mfns )
              break;

          ret = -EPERM;

Thanks
Tiejun