Messages in this thread | | | Subject | Kswapd in 3.2.0-rc5 is a CPU hog | From | "Nikolay S." <> | Date | Wed, 21 Dec 2011 07:10:36 +0400 |
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Hello,
I'm using 3.2-rc5 on a machine, which atm does almost nothing except file system operations and network i/o (i.e. file server). And there is a problem with kswapd.
I'm playing with dd: dd if=/some/big/file of=/dev/null bs=8M
I.e. I'm filling page cache.
So when the machine is just rebooted, kswapd during this operation is almost idle, just 5-8 percent according to top.
After ~5 days of uptime (5 days, 2:10), the same operation demands ~70% for kswapd:
PID USER S %CPU %MEM TIME+ SWAP COMMAND 420 root R 70 0.0 22:09.60 0 kswapd0 17717 nowhere D 27 0.2 0:01.81 10m dd
In fact, kswapd cpu usage on this operation steadily increases over time.
Also read performance degrades over time. After reboot: dd if=/some/big/file of=/dev/null bs=8M 1019+1 records in 1019+1 records out 8553494018 bytes (8.6 GB) copied, 16.211 s, 528 MB/s
After ~5 days uptime: dd if=/some/big/file of=/dev/null bs=8M 1019+1 records in 1019+1 records out 8553494018 bytes (8.6 GB) copied, 29.0507 s, 294 MB/s
Whereas raw disk sequential read performance stays the same: dd if=/some/big/file of=/dev/null bs=8M iflag=direct 1019+1 records in 1019+1 records out 8553494018 bytes (8.6 GB) copied, 14.7286 s, 581 MB/s
Also after dropping caches, situation somehow improves, but not to the state of freshly restarted system: PID USER S %CPU %MEM TIME+ SWAP COMMAND 420 root S 39 0.0 23:31.17 0 kswapd0 19829 nowhere D 24 0.2 0:02.72 7764 dd
perf shows:
31.24% kswapd0 [kernel.kallsyms] [k] _raw_spin_lock 26.19% kswapd0 [kernel.kallsyms] [k] shrink_slab 16.28% kswapd0 [kernel.kallsyms] [k] prune_super 6.55% kswapd0 [kernel.kallsyms] [k] grab_super_passive 5.35% kswapd0 [kernel.kallsyms] [k] down_read_trylock 4.03% kswapd0 [kernel.kallsyms] [k] up_read 2.31% kswapd0 [kernel.kallsyms] [k] put_super 1.81% kswapd0 [kernel.kallsyms] [k] drop_super 0.99% kswapd0 [kernel.kallsyms] [k] __put_super 0.25% kswapd0 [kernel.kallsyms] [k] __isolate_lru_page 0.23% kswapd0 [kernel.kallsyms] [k] free_pcppages_bulk 0.19% kswapd0 [r8169] [k] rtl8169_interrupt 0.15% kswapd0 [kernel.kallsyms] [k] twa_interrupt
P.S.: The message above was written couple of days ago. Now I'm at 10 days uptime, and this is the result as of today PID USER S %CPU %MEM TIME+ SWAP COMMAND 420 root R 93 0.0 110:48.48 0 kswapd0 30085 nowhere D 42 0.2 0:04.36 10m dd
PPS: Please CC me.
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