[Xen-devel] [PATCH 1/2] libxl: fix reporting of maximum memory

[Jim Fehlig <jfehlig@xxxxxxxx>]

The libxl driver reports different values of maximum memory depending
on state of a domain. If inactive, maximum memory value is reported
correctly. When active, maximum memory is derived from max_pages value
returned by the XEN_SYSCTL_getdomaininfolist sysctl operation. But
max_pages can be changed by toolstacks and does not necessarily
represent the maximum memory a domain can use during its active
lifetime.

A better location for determining a domain's maximum memory is the
/local/domain/<id>/memory/static-max node in xenstore. This value
is set from the libxl_domain_build_info.max_memkb field when creating
the domain. Currently it cannot be changed nor can its value be
exceeded by a balloon operation. From libvirt's perspective, always
reporting maximum memory with virDomainDefGetMemoryTotal() will produce
the same results as reading the static-max node in xenstore.

Signed-off-by: Jim Fehlig <jfehlig@xxxxxxxx>
---

As an alternative, libvirt could call libxl_retrieve_domain_configuration
and use the max_memkb field embedded in the libxl_domain_config object.

 src/libxl/libxl_driver.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/src/libxl/libxl_driver.c b/src/libxl/libxl_driver.c
index 3a69720..921cc93 100644
--- a/src/libxl/libxl_driver.c
+++ b/src/libxl/libxl_driver.c
@@ -1640,10 +1640,10 @@ libxlDomainGetInfo(virDomainPtr dom, virDomainInfoPtr 
info)
     if (virDomainGetInfoEnsureACL(dom->conn, vm->def) < 0)
         goto cleanup;
 
+    info->maxMem = virDomainDefGetMemoryTotal(vm->def);
     if (!virDomainObjIsActive(vm)) {
         info->cpuTime = 0;
         info->memory = vm->def->mem.cur_balloon;
-        info->maxMem = virDomainDefGetMemoryTotal(vm->def);
     } else {
         libxl_dominfo_init(&d_info);
 
@@ -1655,7 +1655,6 @@ libxlDomainGetInfo(virDomainPtr dom, virDomainInfoPtr 
info)
         }
         info->cpuTime = d_info.cpu_time;
         info->memory = d_info.current_memkb;
-        info->maxMem = d_info.max_memkb;
 
         libxl_dominfo_dispose(&d_info);
     }
@@ -5172,7 +5171,7 @@ libxlDomainMemoryStats(virDomainPtr dom,
         goto endjob;
     }
     mem = d_info.current_memkb;
-    maxmem = d_info.max_memkb;
+    maxmem = virDomainDefGetMemoryTotal(vm->def);
 
     LIBXL_SET_MEMSTAT(VIR_DOMAIN_MEMORY_STAT_ACTUAL_BALLOON, mem);
     LIBXL_SET_MEMSTAT(VIR_DOMAIN_MEMORY_STAT_AVAILABLE, maxmem);
-- 
2.9.2


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