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On Wed, Oct 12, 2011 at 8:52 PM, Pandu Poluan <pandu@××××××.info> wrote: |
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> Just stumbled upon this blog: |
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> |
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> http://www.webupd8.org/2011/10/increased-performance-in-linux-with.html |
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> |
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> anyone got any experience with zram/compcache on Gentoo? |
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I'm using zram in a gentoo server with only 256mb of RAM, only used |
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for a few weeks so far. It seems to work and the server hasn't crashed |
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yet. :) I have allocated 128MB of compressed swap (64x2, actually, to |
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theoretically utilize both CPU cores for compression at the same time) |
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followed by normal on-disk swap at lower priority. Usually my total |
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swap used is less than 128MB so the real disk swap is rarely touched. |
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It's difficult to say if there is any improved performance, but I |
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haven't experienced any slowdown, which occasionally I did when swap |
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became heavily used in the past. Keep in mind the 128MB zram is the |
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uncompressed size, so the actual amount of RAM used by this should be |
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much less, depending on contents of the swap. Some even recommend |
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using zram equal to the amount of RAM but that idea scares me. |
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After enabling the CONFIG_ZRAM module in kernel 3.0.6, I did this: |
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modprobe zram num_devices=2 |
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echo $((64*1024*1024)) > /sys/block/zram0/disksize |
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echo 1 > /sys/block/zram0/reset |
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mkswap /dev/zram0 |
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swapon -p 11 /dev/zram0 |
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(repeat for /dev/zram1 and so on) |
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you can then swapoff your disk swap partition to empty it, then swapon |
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with lower priority than the zram swap devices. |
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Also note that zram is really just a generic compressed RAM drive. You |
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don't have to use it for swap, you can mkfs anything you like onto it, |
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to use as compressed tmp space or whatever... just know that it'll be |
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gone when you reboot. |
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I think zram can be beneficial in an environment where CPU power is |
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plentiful but RAM needs to be conserved (i.e. fitting more virtual |
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servers onto one physical box). I seem to recall there is a way for a |
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virtual host to utilize zram automatically/transparently for the |
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virtualized guests, but I don't personally know anything about that. |
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