Re: [PATCH] Fix e820 mapping limit

["Daniel P. Berrange" <berrange@redhat.com>]

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On Tue, Dec 12, 2006 at 06:25:25PM +0000, Daniel P. Berrange wrote:
> The changeset '12803:df5fa63490f4da7b65c56087a68783dbcb7944f8' added a new
> hypercall XENMEM_set_memory_map for specifying the e820 mapping. There was
> a small bug in the userspace side of this change though - the e820 mapping
> was specified based on the 'memory_static_min' domain info parameter which
> means the memory map size is clamped to the value 'memory' config option.
> 
> What we actually want is to setup the e820 map limit based on 'maxmem'
> config option, so that we can balloon up the guest to its max limit.
> 
>  eg
>   If we boot with 'memory=400' and 'maxmem=800', the e820 map should be
>   set to 800 MB, and the guest should allocate  only 400 MB at startup.
>   It should then be possible to use 'xm mem-set' after boot to assgin
>   upto this 800 MB.
> 
> Thus, the attached patch fixed the image.py class to setup the e820 mapping
> based on 'memory_static_max' which is in turn based on 'maxmem'. Booting
> with this patch I can verify that the guest kernel sees a 800 MB e820 map,
> so this fixes the initial problem.
> 
> There appears to be a second issue somewhere in the stack though, because
> even if do 'xm mem-set <domid> 600', while the ballon driver in the guest
> will see the 600 MB target, it will still never try to allocate its 
> increased target.

Turns out this was a bug introduced in the refactoring of memory config
parameters from Xen API work. The memory & memmax parameters were getting
initialized the wrong way around. With this fixed & the e820 map fix, 
memory ballooning works perfectly:

  # xm create demo
  Using config file "/etc/xen/demo".
  Going to boot Fedora Core (2.6.18-1.2769.2.2.el5xen)
    kernel: /vmlinuz-2.6.18-1.2769.2.2.el5xen
    initrd: /initrd-2.6.18-1.2769.2.2.el5xen.img
  Started domain demo
  # xm list demo
  Name                                      ID   Mem VCPUs      State   Time(s)
  demo                                      16   410     2     -b----      0.4
  # xm mem-set demo 600
  # xm list demo
  Name                                      ID   Mem VCPUs      State   Time(s)
  demo                                      16   600     2     -b----      4.2


Attaching an updated patch which fixes both the memory ballooning issues
in one go

  Signed-off-by: Daniel P. Berrange <berrange@redhat.com>

Regards,
Dan.
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diff -r f5121d001d1a tools/python/xen/xend/XendDomainInfo.py
--- a/tools/python/xen/xend/XendDomainInfo.py	Sat Dec 09 16:29:52 2006 +0000
+++ b/tools/python/xen/xend/XendDomainInfo.py	Tue Dec 12 14:06:25 2006 -0500
@@ -896,6 +896,10 @@ class XendDomainInfo:
         """Get this domain's target memory size, in KB."""
         return self.info['memory_static_min'] * 1024
 
+    def getMemoryMaximum(self):
+        """Get this domain's maximum memory size, in KB."""
+        return self.info['memory_static_max'] * 1024
+
     def getResume(self):
         return str(self._resume)
 
@@ -1363,9 +1367,9 @@ class XendDomainInfo:
             # Use architecture- and image-specific calculations to determine
             # the various headrooms necessary, given the raw configured
             # values. maxmem, memory, and shadow are all in KiB.
+            memory = self.image.getRequiredAvailableMemory(
+                self.info['memory_static_min'] * 1024)
             maxmem = self.image.getRequiredAvailableMemory(
-                self.info['memory_static_min'] * 1024)
-            memory = self.image.getRequiredAvailableMemory(
                 self.info['memory_static_max'] * 1024)
             shadow = self.image.getRequiredShadowMemory(
                 self.info['shadow_memory'] * 1024,
diff -r f5121d001d1a tools/python/xen/xend/image.py
--- a/tools/python/xen/xend/image.py	Sat Dec 09 16:29:52 2006 +0000
+++ b/tools/python/xen/xend/image.py	Mon Dec 11 16:37:12 2006 -0500
@@ -144,6 +144,14 @@ class ImageHandler:
         architecture- or image-specific code may override this to
         add headroom where necessary."""
         return self.getRequiredAvailableMemory(self.vm.getMemoryTarget())
+
+    def getRequiredMaximumReservation(self):
+        """@param mem_kb The maximum possible memory, in KiB.
+        @return The corresponding required amount of memory to be free, also
+        in KiB. This is normally the same as getRequiredAvailableMemory, but
+        architecture- or image-specific code may override this to
+        add headroom where necessary."""
+        return self.getRequiredAvailableMemory(self.vm.getMemoryMaximum())
 
     def getRequiredShadowMemory(self, shadow_mem_kb, maxmem_kb):
         """@param shadow_mem_kb The configured shadow memory, in KiB.
@@ -539,6 +547,9 @@ class X86_HVM_ImageHandler(HVMImageHandl
     def getRequiredInitialReservation(self):
         return self.vm.getMemoryTarget()
 
+    def getRequiredMaximumReservation(self):
+        return self.vm.getMemoryMaximum()
+
     def getRequiredShadowMemory(self, shadow_mem_kb, maxmem_kb):
         # 256 pages (1MB) per vcpu,
         # plus 1 page per MiB of RAM for the P2M map,
@@ -553,7 +564,7 @@ class X86_Linux_ImageHandler(LinuxImageH
     def buildDomain(self):
         # set physical mapping limit
         # add an 8MB slack to balance backend allocations.
-        mem_kb = self.getRequiredInitialReservation() + (8 * 1024)
+        mem_kb = self.getRequiredMaximumReservation() + (8 * 1024)
         xc.domain_set_memmap_limit(self.vm.getDomid(), mem_kb)
         return LinuxImageHandler.buildDomain(self)
 

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