LowFree on DL585 w/ 20GB of RAM

[Eric Singer]

We have a DL585 with 20 GB of RAM running Redhat AS 3.0 update 7 hugemen kernel (2.4.21-40.ELhugemem). I was reading through Werner Puschitz Article http://www.puschitz.com/TuningLinuxForOracle.shtml and started to get concerned about the LowFree memory amount for this server. We're running 4 Oracle databases on this server. Should I be alarmed or this this okay for a hugemem kernel?

Here's the meminfo from that server.

cat /proc/meminfo
total: used: free: shared: buffers: cached:
Mem: 22993158144 22946856960 46301184 0 105811968 19917611008
Swap: 6396313600 0 6396313600
MemTotal: 22454256 kB
MemFree: 45216 kB
MemShared: 0 kB
Buffers: 103332 kB
Cached: 19450792 kB
SwapCached: 0 kB
Active: 16706384 kB
ActiveAnon: 3930428 kB
ActiveCache: 12775956 kB
Inact_dirty: 3181252 kB
Inact_laundry: 498268 kB
Inact_clean: 485016 kB
Inact_target: 4174184 kB
HighTotal: 18874364 kB
HighFree: 28596 kB
LowTotal: 3579892 kB
LowFree: 16620 kB
SwapTotal: 6246400 kB
SwapFree: 6246400 kB
CommitLimit: 17473528 kB
Committed_AS: 9450788 kB
HugePages_Total: 0
HugePages_Free: 0
Hugepagesize: 2048 kB

[Ivan Ferreira]

You don't have to worry about it, from that output, you can see that there are high ammount of memory used by buffers and cache (105811968 19917611008). This is normal and it's good.

Linux will always try use all memory, this is efficient, if not used by applications, it's used as buffers/cache.

[Eric Singer]

Thanks for the reply, I was really pointing out the "LowFree: 16620 kB" figure that had me worried.

[Ivan Ferreira · Accepted solution]

"Low memory starvation happens when LowFree in /proc/meminfo becomes very low accompanied by a sudden spike in paging activity"

Check the paging activity with:

vmstat 5

If you don't have continuous page in AND page outs, this should not be a problem.

[Eric Singer]

Vmstat 5 is not showing any si and so activity, so I guess we're good. Just thought this would explain a server hang we had about a week and a half ago.

[Ivan Ferreira]

Install the sysstat package and let sar capture performance information. You can review later this information for troubleshooting.