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Am Thu, 25 May 2017 11:46:45 -0700 |
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schrieb Ian Zimmerman <itz@×××××××.net>: |
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> On 2017-05-24 19:05, Kai Krakow wrote: |
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> |
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> > To get in line with Rich Freeman: I didn't want to imply that zswap |
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> > only works with swap, neither that tmpfs only works with swap. Both |
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> > work without. But if you want to put some serious amount of data |
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> > into tmpfs, you need swap as a backing device sooner or later. |
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> |
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> Looking at zswap, I have several questions |
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> (even after reading linux/Documentation/vm/zswap.txt). |
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> |
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> 1. How does it know which swap device to use as backing store, if |
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> any? Clearly at boot time no swap configuration exists, even if |
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> initrd/initramfs is used, which here it is not. So when the kernel |
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> sees zswap.enable=1 in the command line, what happens? |
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You simply don't assign a swap device to zswap. It's transparently |
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inserted into the swapping chain of the kernel. Thus pages are first |
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compressed, and later swapped out by normal kernel processing. |
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> 2. The doc says it can be turned on at runtime by means of |
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> /sys/module/zswap/parameters/enabled. But kconfig doesn't make it |
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> possible to build the support as a module, only built-in, and so it is |
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> not surprising that this path doesn't exist. |
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I wonder why this doesn't exist. All my builtin modules have their |
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parameters in /sys/module: |
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|
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# lsmod | fgrep zswap | wc -l |
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0 |
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# ls -ald /sys/module/zswap |
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drwxr-xr-x 3 root root 0 26. Mai 07:54 /sys/module/zswap |
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> 3. It seems to require zbud to also be turned on, but this is not |
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> enforced by kconfig. Is this a bug or what? |
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No idea, I enabled it... |
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> 4. Quoting: |
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> |
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> Zswap seeks to be simple in its policies. Sysfs attributes allow |
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> for one user controlled policy: |
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> * max_pool_percent - The maximum percentage of memory that the |
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> compressed pool can occupy. |
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> |
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> Does this mean this is another (hypothetical) node in |
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> /sys/module/zswap/parameters/ ? |
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grep ^ /sys/module/zswap/parameters/* |
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/sys/module/zswap/parameters/compressor:lzo |
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/sys/module/zswap/parameters/enabled:Y |
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/sys/module/zswap/parameters/max_pool_percent:20 |
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/sys/module/zswap/parameters/zpool:zbud |
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This also implies that zbud it required for zswap to even operate. If |
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you didn't include it, it may be the reason why zswap is missing |
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in /sys/module. |
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-- |
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Regards, |
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Kai |
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Replies to list-only preferred. |
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