25

How can I check to verify that zswap is enabled and working on my system?

Rucent88
  • 1,900
  • 3
  • 22
  • 28

2 Answers2

25
dmesg | grep zswap

That should be all you need to know if it's running. You should see a message along the lines of:

[    1.241302] zswap: loading zswap
[    1.241306] zswap: using zbud pool
[    1.241310] zswap: using lzo compressor

You can see what it's doing with the following:

$ sudo grep -R . /sys/kernel/debug/zswap
/sys/kernel/debug/zswap/stored_pages:0
/sys/kernel/debug/zswap/pool_total_size:0
/sys/kernel/debug/zswap/duplicate_entry:0
/sys/kernel/debug/zswap/written_back_pages:0
/sys/kernel/debug/zswap/reject_compress_poor:0
/sys/kernel/debug/zswap/reject_kmemcache_fail:0
/sys/kernel/debug/zswap/reject_alloc_fail:0
/sys/kernel/debug/zswap/reject_reclaim_fail:0
/sys/kernel/debug/zswap/pool_limit_hit:0

The key parameters to look out for are stored_pages which is the number of compressed pages and written_back_pages which is the number of pages which have been written out to the swap file.

davefiddes
  • 105
  • 3
Oli
  • 289,791
  • 117
  • 680
  • 835
  • 1
    `dmesg | grep zswap` shows nothing on my system (Ubuntu 18.04), but `sudo grep -r . /sys/kernel/debug/zswap` shows zswap is working. – scoobydoo Jul 12 '19 at 05:21
  • @scoobydoo Same as you. Do you know the reason? – ife Jun 09 '21 at 03:54
  • @吴毅凡 not sure but now with Ubuntu 20.04 `dmesg | grep zswap` does show that zswap is loaded: `[ 1.802721] zswap: loaded using pool lzo/zbud` – scoobydoo Jun 10 '21 at 07:33
  • I am looking at this data, but still not sure what it means: What is `stored_pages`, `written_back_pages`, `pool_total_size`? – ctrl-alt-delor Feb 20 '22 at 11:40
6

Shell expansion is a weird thing sometimes. grep fortunately have a recursive option so to simplify it:

sudo grep -r . /sys/kernel/debug/zswap
Alexey Vazhnov
  • 424
  • 3
  • 14
Nikolay Naydenov
  • 61
  • 1
  • 1