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Date: Sat, 19 Jan 2008 20:32:40 +0100
From: Kris Kennaway <kris@FreeBSD.org>
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Subject: Re: Swapping caused by very large (regular) file size
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Thomas Hurst wrote:
> * Thomas Hurst (tom.hurst@clara.net) wrote:
> 
>> * Kris Kennaway (kris@FreeBSD.org) wrote:
>>
>>>> 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 ;)
>> 7 does indeed seem to resolve this.  Also, no sign of corruption on my
>> Marvell 88SX6081, at least during serial read tests.  I'll test with
>> a level 0 dump tonight; my writes go via tee to the filesystem and
>> sha1(1) so I should pick up any silent corruption.
> 
> Doh:
> 
>   http://voi.aagh.net/voi.nightsdawn.sf-swap-day.png
> 
> Making a 100GB dump of /usr, then making a par2 set results in minor
> paging activity all through it.  Running sha1 over the dump has a
> similar effect.  It settles around 2.5MB swap now, though; 6 would
> quickly settle around 10MB, so it does appear to be improved somewhat;
> top isn't showing fetchmail and friends as <swapped> for instance.
> 
> This is off a single ata(4) disk, which peaks around 65MB/s.
> 
> sha1 file results match that from the dump|tee file|sha1 > file.sha1
> at least :)
> 

I don't understand your test procedure, can you elaborate?

Kris