System information
186 System Analysis and Tuning Guide
ti-socket servers are NUMA machines. NUMA is a secondary concern to managing
swapping and caches in terms of performance, and there are lots of documents about
improving NUMA memory allocations. One particular parameter interacts with page
reclaim:
/proc/sys/vm/zone_reclaim_mode
This parameter controls whether memory reclaim is performed on a local NUMA
node even if there is plenty of memory free on other nodes. This parameter is au-
tomatically turned on on machines with more pronounced NUMA characteristics.
If the VM caches are not being allowed to fill all of memory on a NUMA ma-
chine, it could be due to zone_reclaim_mode being set. Setting to 0 will disable
this behavior.
15.5 Monitoring VM Behavior
Some simple tools that can help monitor VM behavior:
1. vmstat: This tool gives a good overview of what the VM is doing. See Section2.1.1,
“vmstat” (page10) for details.
2. /proc/meminfo: This file gives a detailed breakdown of where mem-
ory is being used. See Section2.4.2, “Detailed Memory Usage: /proc/
meminfo” (page29) for details.
3. slabtop: This tool provides detailed information about kernel slab memory
usage. buffer_head, dentry, inode_cache, ext3_inode_cache, etc. are the major
caches. This command is available with the package procps.