Re: free RAM not being used for page cache

On Tue, Aug 5, 2014 at 8:27 AM, Shaun Thomas <sthomas(at)optionshouse(dot)com>
wrote:

> On 07/30/2014 12:51 PM, Kevin Goess wrote:
>
> A couple months ago we upgraded the RAM on our database servers from
>> 48GB to 64GB. Immediately afterwards the new RAM was being used for
>> page cache, which is what we want, but that seems to have dropped off
>> over time, and there's currently actually like 12GB of totally unused RAM.
>>
>
> What version of the Linux kernel are you using? We had exactly this
> problem when we were on 3.2. We've since moved to 3.8 and that solved this
> issue, along with a few others.
>

Debian squeeze, still on 2.6.32.

>
> If you're having the same problem, this is not a NUMA issue or in any way
> related to zone_reclaim_mode. The memory page aging algorithm in pre 3.7 is
> simply broken, judging by the traffic on the Linux Kernel Mailing List
> (LKML).
>

Darn, really? I just learned about the "mysql swap insanity" problem and
noticed that all the free memory is concentrated on one of the two nodes.

$ numactl --hardware
available: 2 nodes (0-1)
node 0 cpus: 0 2 4 6
node 0 size: 32768 MB
node 0 free: 9105 MB
node 1 cpus: 1 3 5 7
node 1 size: 32755 MB
node 1 free: 259 MB

$ free
total used free shared buffers cached
Mem: 66099280 56565804 9533476 0 11548 51788624

I haven't been able to get any traction on what that means yet though.

--
Kevin M. Goess
Software Engineer
Berkeley Electronic Press
kgoess(at)bepress(dot)com

510-665-1200 x179
www.bepress.com

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