Re: High CPU load with kswapd and heavy disk I/O

[Nuno Silva <nuno.silva@vgertech.com>]

Hi!

Ken Savage wrote:
> Short version:
> ----------------
> kernels 2.4.17 --> 2.4.21
> Dual Athlon SMP system
> 4GB RAM, 2GB swap
> 3ware RAID, filled with millions of files across thousands of directories.
> reiserfs 3.6
> 
> The following command is guaranteed to lock out the box by activating
> kswapd to >95% CPU, blocking out pings, everything.
> 
>     find /RAID/data/ -type f -mtime +180 | xargs rm
> 

Can you send before, during and after:
cat /proc/meminfo
cat /proc/slabinfo

And maybe:
vmstat 1

Real kernel hackers (not me...) will find that information very usefull ;)

Regards,
Nuno Silva


> Details:
> ----------
> Applying the rmap patch seems to prevent kswapd from hogging the CPU,
> but causes it to freeze up for some other reason.  (The server is remote,
> so I can't view the console.)  Likewise 2.6.0-test* causes freezeups.
> Mind you, the server is under a fair bit of CPU and disk load -- hundreds
> of processes/threads all actively running.  I suspect something in rmap
> has made its way into 2.6 and our usage pattern is triggering the same
> fault in both places.
> 
> It appears as though the system is unable to efficiently clean up disk
> buffer memory when called on to do so.  In the Documentation/, there
> is mention of a buffermem sysctl, but that's nowhere to be found.
> It's obviously been removed/replaced...  Is there any way to limit the
> amount of buffer memory used by the system, that way if/when kswapd
> needs to reclaim it, there's very little work for it to do?
> 
> Admittedly, that's just masking the problem, as opposed to solving it.
> Any idea why kswapd is having such a tough go??  Known solutions
> for this problem?
> 
> TIA,
> 
> Ken
> 
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