从日志来看，系统内存leak导致out of memory。
Oct 30 14:22:35 xenserver-21622 kernel: [36474919.505097] lowmem_reserve[]: 0 0 0 0
Oct 30 14:22:35 xenserver-21622 kernel: [36474919.505104] DMA: 566*4kB 3*8kB 6*16kB 1*32kB 1*64kB 0*128kB 0*256kB 1*512kB 0*1024kB 0*2048kB 0*4096kB = 2992kB
Oct 30 14:22:35 xenserver-21622 kernel: [36474919.505121] Normal: 7335*4kB 30*8kB 19*16kB 5*32kB 0*64kB 1*128kB 0*256kB 0*512kB 0*1024kB 0*2048kB 0*4096kB = 30172kB
Oct 30 14:22:35 xenserver-21622 kernel: [36474919.505144] HighMem: 4601*4kB 7437*8kB 11764*16kB 7771*32kB 4097*64kB 1964*128kB 1047*256kB 624*512kB 289*1024kB 186*2048kB 212*4096kB = 3161132kB
Oct 30 14:22:35 xenserver-21622 kernel: [36474919.505164] 16719 total pagecache pages
Oct 30 14:22:35 xenserver-21622 kernel: [36474919.505167] 0 pages in swap cache
Oct 30 14:22:35 xenserver-21622 kernel: [36474919.505170] Swap cache stats: add 91, delete 91, find 68/73
Oct 30 14:22:35 xenserver-21622 kernel: [36474919.505174] Free swap = 524248kB
Oct 30 14:22:35 xenserver-21622 kernel: [36474919.505177] Total swap = 524280kB
Oct 30 14:22:35 xenserver-21622 kernel: [36474919.514944] 1050624 pages RAM
Oct 30 14:22:35 xenserver-21622 kernel: [36474919.514953] 857090 pages HighMem
Oct 30 14:22:35 xenserver-21622 kernel: [36474919.514956] 39028 pages reserved
Oct 30 14:22:35 xenserver-21622 kernel: [36474919.514959] 41189 pages shared
Oct 30 14:22:35 xenserver-21622 kernel: [36474919.514962] 195743 pages non-shared
Oct 30 14:22:35 xenserver-21622 kernel: [36474919.514966] Out of memory: kill process 12051 (fe) score 48887 or a child
Oct 30 14:22:35 xenserver-21622 kernel: [36474919.514972] Killed process 12052 (xapi)
在xenserver 6.2 平台这是一个known issue，具体可参考KB ：
http://support.citrix.com/article/CTX138833
Xenserver 62E004 的hotfix可解kernel memory leak的问题，目前建议客户只有将vm全部关机（因为memory leack，导致migration fail），然后安装该hotfix。
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1. Download the update file to a known location.
2. Extract the xsupdate file from the zip.
3. Upload the xsupdate file to the Pool Master by entering the following commands:
(Where hostname is the Pool Master's IP address or DNS name.)
xe patch-upload -s
4. XenServer assigns the update file a UUID which this command prints. Note the UUID.
5579f1f0-ff83-11e2-b778-0800200c9a66
5.
6. Apply the hotfix to all hosts in the pool, specifying the UUID of the hotfix:
xe -s
7.
8. Verify that the update was applied by using the patch-list command.
xe patch-list -s
9. If the update has been successful, the hosts field will contain the UUIDs of the hosts this patch was successfully applied to. This should be a complete list of all hosts in the pool.
10. To verify in XenCenter that the update has been applied correctly, select the Pool, and then click the General tab. This displays the Pool properties. In the Updates section, ensure that the update is listed as Fully Applied.
11. The hotfix is applied to all hosts in the pool, but it will not take effect until each host has been rebooted. For each host, migrate the VMs that you wish to keep running, and shutdown the remaining VMs before rebooting the host.
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操作：
1，打补丁前检查：
[root@xenserver-21652 ~]# xe patch-list -s 192.168.216.52 -u root -pw ****** name-label=XS62E004
空
2，
[root@xenserver-21652 ~]# xe patch-upload -s 192.168.216.52 -u root -pw ****** file-name=/root/XS62E004.xsupdate
5579f1f0-ff83-11e2-b778-0800200c9a66
[root@xenserver-21652 ~]# xe -s 192.168.216.52 -u root -pw ****** patch-pool-apply uuid=5579f1f0-ff83-11e2-b778-0800200c9a66
[root@xenserver-21652 ~]# xe patch-list -s 192.168.216.52 -u root -pw ****** name-label=XS62E004
uuid ( RO) : 5579f1f0-ff83-11e2-b778-0800200c9a66
name-label ( RO): XS62E004
name-description ( RO): Public Availability: Fixes for Dom0 kernel issues
size ( RO): 35766769
hosts (SRO): 6acc1e95-7481-4cfc-a0b7-96d75a3db1ad
after-apply-guidance (SRO): restartHost
[root@xenserver-21652 ~]# xe host-list
uuid ( RO) : 6acc1e95-7481-4cfc-a0b7-96d75a3db1ad
name-label ( RW): xenserver-21652
name-description ( RW): Default install of XenServer
Ok