Manfred Spraul wrote:
Linux doesn't release the swap file page when a page is read back: If a page is only read by the user space app, then the swapped out page remains valid, and thus the kernel can skip the write to disk on the next swapout. Thus if you are paranoid, you must limit the total address space to the size of your swap files.
It is strange to choose 50% of RAM plus swap (what if your spam is
small). I thought it would be 100% of RAM plus the swap that exceeds RAM
size.
If your swap space (your wrote "spam" - I assume a typo) is small, then you'll run into problems. It's recommended that your swap space should be 2*physical memory. I assume that many oom killer reports are from system with too small swap files, and then an updatedb run pushes the system into oom.
I believe that the swap slot can be subsequently freed, though. In theory your available virtual memory should be (almost) RAM+swap. In practice, Linux can run too close to that limit, (or way over it if you turn the checks off). But restricting the maximum possible pages to RAM/2 + swap should normally be fine. IANAKH, though.
Also note that the truly bad thing about the OOM killer is that it can affect a process that is not making any new memory demands at all.
cheers
andrew
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