Re: 2.4.28 - kswapd excessive cpu usage under heavy IO

From: Marcelo Tosatti (marcelo.tosatti_at_cyclades.com)
Date: 12/06/04

  • Next message: Gregory Giguashvili: "RE: Correctly determine amount of "free memory"" 
    Date:	Mon, 6 Dec 2004 10:57:16 -0200
To: Per Jessen <per@computer.org>

    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.

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  • Next message: Gregory Giguashvili: "RE: Correctly determine amount of "free memory""