kswapd is having a party
My question for today: does anyone know what kswapd actually does?
This morning, my workstation (linux ia64 2.6.0-test3) was fairly lightly loaded:
08:28:50 up 2 days, 1:49, 4 users, load average: 1.77, 1.79, 1.20
Mem: 2062032k total, 1916368k used, 145664k free, 119952k buffers Swap: 2016112k total, 1984k used, 2014128k free, 697920k cached
As you can see, there was gobs of RAM I wasn't using.
Anyway, as I was enjoying my tasty breakfast cereal, I noticed kswapd decided to wake up and say hello:
29109 duraid 25 0 400m 394m 6272 R 95.0 19.6 3:07.09 lsh 29108 duraid 19 0 404m 399m 6272 R 48.3 19.8 3:15.89 lsh 13 root 15 0 0 0 0 R 17.2 0.0 0:26.47 kswapd0
29148 duraid 25 0 400m 394m 6272 R 93.9 19.6 3:13.23 lsh 29147 duraid 20 0 404m 399m 6272 S 21.1 19.8 3:12.16 lsh 13 root 15 0 0 0 0 R 18.1 0.0 0:38.02 kswapd0
29148 duraid 25 0 400m 394m 6272 R 75.9 19.6 5:32.66 lsh 29147 duraid 18 0 404m 399m 6272 S 62.0 19.8 4:08.49 lsh 13 root 16 0 0 0 0 R 16.4 0.0 0:50.08 kswapd0
29147 duraid 25 0 404m 397m 6272 R 93.9 19.7 6:23.87 lsh 29148 duraid 25 0 400m 392m 6272 R 75.4 19.5 9:00.72 lsh 13 root 15 0 0 0 0 R 21.0 0.0 1:03.84 kswapd0
It seems I can make kswapd use fairly nontrivial amounts of CPU time by
running a perfectly innocent userland program. lsh is a raytracer I'm starting to work on. It's a standard C program, which uses MPI (I'm using LAM 7.0). The parallelism is trivial - each process renders a section of the image (divided vertically), line-at-a-time. The imbalance in CPU time between the processes is due to some sections of the scene being less interesting than others and finishing more quickly.
Does anyone have _any_ idea what kswapd might actually be doing? I
checked: not a single page was swapped in our out througout the duration of this test. Is there a chance that spinning on some lock (I have no idea how LAM does its synchronization), or perhaps even just idling, might be counted as kswapd0?
Curious,
Duraid
Attached: a snap of gkrellm. the light blue is kswapd, the dark blue is my program, the black is idle time.
Quoted 5 lines · Duraid Madina
Does anyone have _any_ idea what kswapd might actually be doing? I
checked: not a single page was swapped in our out througout the duration of this test. Is there a chance that spinning on some lock (I have no idea how LAM does its synchronization), or perhaps even just idling, might be counted as kswapd0?
I'd look for dirty memory; kswapd does do some page cleaning, though pdflush is supposed to do most of it.
-- wli
Quoted 5 lines · Duraid Madina
Quoted 5 lines
Does anyone have _any_ idea what kswapd might actually be doing? I
checked: not a single page was swapped in our out througout the duration of this test. Is there a chance that spinning on some lock (I have no idea how LAM does its synchronization), or perhaps even just idling, might be counted as kswapd0?
Quoted 2 lines · William Lee Irwin III
I'd look for dirty memory; kswapd does do some page cleaning, though pdflush is supposed to do most of it.
Also, please log vmstat and take regular snapshots of /proc/vmstat.
-- wli