Swapping caused by very large (regular) file size

Thomas Hurst tom.hurst at clara.net
Mon Jan 14 18:20:37 PST 2008

* John Baldwin (jhb at freebsd.org) wrote:

> 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.

Excellent.  I've been seeing this behavior for a long time, mostly on
backup runs (RAID-1 amr SATA -> 1 disk Marvell ata).  It's pretty odd
seeing a system with 8G of memory, 60% of which is just cache, swap out
half a dozen things for no apparant reason.  And to think, people on
FreeNode ##freebsd just insisted I had a misconfigured system ;)

My other IO related issue with 6 is IO to independent amr arrays
blocking each other; e.g. daily run's find over amrd0 will invariably
cause reads from amrd1 and amrd2 to freeze for seconds at a time (pr
114438).  I'll be very interested to see if 7 fixes that.

Thomas 'Freaky' Hurst

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