Swapping caused by very large (regular) file size

Adam McDougall mcdouga9 at egr.msu.edu
Wed Jan 16 13:29:00 PST 2008

On Sat, Jan 12, 2008 at 12:05:38AM -0500, John Baldwin wrote:

  On Friday 11 January 2008 10:31:47 pm Peter Jeremy wrote:
  > On Fri, Jan 11, 2008 at 06:44:20PM +0100, Kris Kennaway wrote:
  > >Ian West wrote:
  > >> dd if=/dev/zero bs=32768 of=junkfile count=100000 seems to do it quite
  > >> reliably on all the boxes I have tested ?
  > >
  > >I am unable to reproduce this on 7.0.
  > I can't reproduce it on 6.3-PRERELEASE/amd64 with 1GB RAM.
  > vmstat -s;dd if=/dev/zero bs=32768 of=junkfile count=100000;vmstat -s
  > shows the following changes:
  >         2 swap pager pageins
  >         2 swap pager pages paged in
  >         4 swap pager pageouts
  >         5 swap pager pages paged out
  >        24 vnode pager pageins
  >        78 vnode pager pages paged in
  >         0 vnode pager pageouts
  >         0 vnode pager pages paged out
  You may not have a fast enough disk.  We have noticed an issue at work
  but only on faster controllers (e.g. certain mfi(4) drive configurations)
  when doing I/O to a single file like the dd command mentioned causes the
  buffer cache to fill up.  The problem being that we can't lock the vm
  object to recycle pages when we hit the limit that is supposed to prevent
  this because all the pages in the cache are for the file (vm object) we
  are working on.  Stephan (ups@) says this is fixed in 7.  The tell-tale
  sign that we see is pagedaemon starts chewing up lots of CPU as the kernel
  tries to realign the page queues along with I/O throughput going down the
  toilet and being very erratic.
  John Baldwin

These are the same symptoms as on a friend's system a little while back with 6.x.
I forwarded him a message from this thread and he agreed, and he confirmed 
having an mfi.

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