Messages in this thread |  | | Date | Wed, 21 Mar 2012 10:58:16 -0400 | From | Rik van Riel <> | Subject | Re: extreme system load [kswapd] |
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On 03/20/2012 05:08 AM, Karol Šebesta wrote: > Hello @All, > > We have a problem on our production machine with high CPU utilization > caused by kswapd3 daemon. Server is 128GB of physical memory and 81GB > of SWAP.
> # free -m > total used free shared buffers cached > Mem: 128989 75577 53412 0 416 57131 > -/+ buffers/cache: 18029 110960 > Swap: 81919 31310 50609 > #
Looks like a combination of NUMA and the workload thrown at the system. You did not post any vmstat output, or info on the size of your Oracle SGA, so I will take some wild guesses here :)
Not only are you 31GB in swap, you also have 53GB of memory free. Additionally, only kswapd3 is very busy, while kswapd on the other NUMA nodes do not even show up in top.
I would guess that the value of /proc/sys/vm/zone_reclaim_mode is 1, causing the system to reclaim memory from the NUMA node where things are running, instead of overflowing memory allocations into other NUMA nodes.
Setting zone_reclaim_mode to 0 could resolve some of your issues.
Another, more fundamental, issue is that on older kernels we mix page cache and process pages on the same LRU lists. This causes the pageout code to scan over many pages that we do not want to evict, increasing CPU use by kswapd and other processes invoking the pageout code.
That issue got fixed in newer kernels, including the kernel in RHEL 6.
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