You can also try to use vm.dirty_ratio = 40 or vm.dirty_ratio = 50 and it might help with the reclaim, I can't guarantee, but it might. Try also setting vm.min_free_kbytes to 65536 not 45056, this also will force the kernel to free up a bit more memory which in terms will trick it to actually have memory. Hope it helps.

Thank you Robert. I will try that and see how it goes. For the moment all is ok and system is running for a few days and still not swapping.

I just got a new spike but not enough to start OOM.

Why is mem usage going down and swap usage is going up?

http://i.imgur.com/PyT35ie.jpg

Left side is before the spike. Right side is just 5 minutes later.

http://pastebin.com/AmSxhVJC

That is how swap works. Imagine having two cups, one being filled with water from time to time and the other is empty. When one cup gets near full, pour some of it into the second cup. The first cup then has less water in it.

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That’s a good point Joe. Got that now.

I still don’t understand the sudden need to swap that much.

A little more detailed info in that memory is set in blocks, and then those blocks will be assigned to processes. It take time to move from RAM to disk and during the transition the related blocks will most often be locked out from the process. Bear in mind a single process might be assigned many blocks, not simply one, and it is better to have all the blocks in either RAM or swap, not split between the two. The simplest way to track this with the least interruptions to the overall system is to find the process that has the largest number of blocks assigned to it and move those blocks to swap. Thus a large amount of RAM is freed up in one single large move operation rather than a bunch of smaller move operations.

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The flow from swap to ram is not driven by the mere availability of free ram.

So if there is a temporary need to swap and that need goes away, then you see exactly what you did see: Swap use goes up, then before the next time you sample ram use goes down and swap use stays up.

So any short lasting new load on ram will cause that long lasting increase in swap use and decrease in ram use that you observed.

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