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zswap makes swap useful on the server as it results in gradual slowdown when the system has used all the ram. And if the system runs at 75% of CPU, then there i

by fpoling 10y ago

zswap makes swap useful on the server as it results in gradual slowdown when the system has used all the ram. And if the system runs at 75% of CPU, then there is room for such slowdown.

twic 10y ago
I hadn't heard of zswap [0]: "Zswap is a lightweight compressed cache for swap pages. It takes pages that are in the process of being swapped out and attempts to compress them into a dynamically allocated RAM-based memory pool. [...] Zswap is a new feature as of v3.11 [...] zswap is a work in progress and should be considered experimental." The return of RAM Doubler! The naming is initially confusing if you're already familiar with ZFS, especially: "Zswap makes use of zpool for the managing the compressed memory pool" [0] https://www.kernel.org/doc/Documentation/vm/zswap.txt https://www.kernel.org/doc/Documentation/vm/zswap.txt
- lmns 10y ago
  It's actually quite useful on many consumer devices, especially those with multiple cores. Most of the time I'm happy I can trade a few CPU cycles for better I/O performance.
mrmondo 10y ago
yes, we run ZRAM of every single server we have, its fantastic and we don't have swap anywhere. It's worth noting though that vm.swappiness is set to 0 then ZRAM wont be used, it must be set to 1 or higher unless you're using a really old kernel (pre 3.5).
- mwpmaybe 10y ago
  zram[0] is not the same thing as zswap[1]. 0. https://en.wikipedia.org/wiki/Zram https://en.wikipedia.org/wiki/Zram 1. https://en.wikipedia.org/wiki/Zswap https://en.wikipedia.org/wiki/Zswap
- fpoling 10y ago
  I have found that zswap behaves much better than zram when the size of the used ram approaches 150% of RAM. In theory zram compresses better as zswap has very simple mapping for the location of its cache of compressed pages leading to space underutilization. But, as it has real backing store, it can evict unused pages allowing bigger chunk of uncompressed memory for running applications.

by fpoling 10y ago

zswap makes swap useful on the server as it results in gradual slowdown when the system has used all the ram. And if the system runs at 75% of CPU, then there is room for such slowdown.

twic 10y ago

I hadn't heard of zswap [0]: "Zswap is a lightweight compressed cache for swap pages. It takes pages that are in the process of being swapped out and attempts to compress them into a dynamically allocated RAM-based memory pool. [...] Zswap is a new feature as of v3.11 [...] zswap is a work in progress and should be considered experimental." The return of RAM Doubler! The naming is initially confusing if you're already familiar with ZFS, especially: "Zswap makes use of zpool for the managing the compressed memory pool" [0] https://www.kernel.org/doc/Documentation/vm/zswap.txt https://www.kernel.org/doc/Documentation/vm/zswap.txt

lmns 10y ago
It's actually quite useful on many consumer devices, especially those with multiple cores. Most of the time I'm happy I can trade a few CPU cycles for better I/O performance.

mrmondo 10y ago

yes, we run ZRAM of every single server we have, its fantastic and we don't have swap anywhere. It's worth noting though that vm.swappiness is set to 0 then ZRAM wont be used, it must be set to 1 or higher unless you're using a really old kernel (pre 3.5).

mwpmaybe 10y ago
zram[0] is not the same thing as zswap[1]. 0. https://en.wikipedia.org/wiki/Zram https://en.wikipedia.org/wiki/Zram 1. https://en.wikipedia.org/wiki/Zswap https://en.wikipedia.org/wiki/Zswap
fpoling 10y ago
I have found that zswap behaves much better than zram when the size of the used ram approaches 150% of RAM. In theory zram compresses better as zswap has very simple mapping for the location of its cache of compressed pages leading to space underutilization. But, as it has real backing store, it can evict unused pages allowing bigger chunk of uncompressed memory for running applications.