Re: 2.4.28 - kswapd excessive cpu usage under heavy IO

[Marcelo Tosatti <marcelo.tosatti@cyclades.com>]

Hi,

On Mon, Dec 06, 2004 at 12:14:48PM +0100, Per Jessen wrote:
> (apologies if this is sent more than once)
> I've found similar incidences in the archives, but none that indicates that a
> solution was found. 
> I'm seeing excessive cpu usage by kswapd on a 4way 500MHZ Xeon with 2GB RAM.

What is your workload? Except the massive amount of inode's/dentries in your 
system do you have anonymous memory hungry applications running? 

If you do have a significant amount of anonymous pages on your system you might
want to try 2.4.29-pre1 which contains a VM change which should decrease their 
impact on the VM page freeing efforts (including kswapd CPU usage).

Since you have massive amount of inodes/dentries you might want to tweak
/proc/sys/vm/vm_vfs_scan_ratio (increase from 6 to 10 and so on...)

>  A find in a directory containing perhaps 6-700,000 files makes the box almost
> grind to a halt.  In 12days uptime, kswap has used 590:43.82, and during the
> find-exercise usually runs with 90-100% util.

Can you boot with profile=2 and use readprofile tool to read the functions which 
are using most CPU time with

readprofile | sort -nr +2 | head -20

Do that on a 2.4.28 and 2.4.29-pre1 kernels.

> The file-system is 150GB with JFS117 on a software-RAID5 - not exactly optimal,
> I agree, but reasonably workable.
> 
> I've read that 2.6 has significant improvements in this area, but upgrading is
> not currently an option.  

Yes, v2.6 VM design is way better than v2.4's in many aspects.