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Peter Humphrey wrote: |
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> On Wednesday 08 July 2009 14:51:04 Frank Peters wrote: |
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>> Or is the system designed to extend the tmpfs through swapping? |
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> |
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> Sort of. If the tmpfs becomes full, part of it that isn't needed at the |
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> moment is swapped to disk, exactly as if it had been program space. |
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> |
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This is not completely accurate. The size limit you set on the tmpfs is |
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the size of the filesystem. df will show that many bytes free, and if |
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you write one byte more you'll get an error that the filesystem is full. |
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Completely independent from this, the kernel will swap memory out to |
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disk when needed. If I have 300GB of RAM, and a 1GB tmpfs, and 5GB of |
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resident programs, most likely nothing will be swapped up until the time |
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the tmpfs is full. At that point the tmpfs will report that it is full, |
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and still nothing will have swapped (most likely - the kernel can still |
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swap stuff out in favor of cache even if the RAM is 99.999% unutilized). |
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If I have 2GB of RAM and 10GB of tmpfs, then the system is guaranteed |
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to swap long before that tmpfs fills up. |
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In general, the guideline is to set your tmpfs up to be big enough to |
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handle a large emerge (such as openoffice/firefox) - at least a few GB. |
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Be sure to have enough swap space to handle the size of your full |
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tmpfs + anything you're likely to be running - amount of physical RAM. |
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If you run out of swap before you run out of tmpfs space, then the |
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next write to the tmpfs is going to trigger the OOM killer. I'm not |
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sure how tmpfs is prioritized by the OOM killer, but suffice it to say |
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you're either going to lose tmpfs data or running processes. If you |
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can't make your swap big enough, then you could set a smaller tmpfs and |
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then just unmount it before emerging large programs. Note that more |
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than just portage ends up in /var/tmp - I'm not sure what kde does if |
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its cache disappears mid-session. |
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Again, unless you're running in unusual circumstances I don't think you |
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need to worry about the number of tmpfs inodes. |
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