Peter:
Would you describe your swap configuration? The output from df -hlk and
swap -l would be helpful.
Thanks,
-j
On Wed, Aug 15, 2007 at 08:17:05AM -0700, Peter C. Norton wrote:
> We use solaris 10 at my company, but I noticed this behavior is the
> same/worse on sxde, and I wanted to know if someone could test this on
> a recent nevada build.
>
> The problem:
>
> We have long used tmpfs for /tmp on systems where we want to provide
> our uses with a scratch space for them to put small files. This does
> get abused occasionally, but for that use it has been fine.
>
> The other day, we saw some puzzling behavior. Specifically, when a
> system with a lot of memory (16gb) had a 10gb file in /tmp, and a few
> large processes running (say 2 gb in 2 processes for the sake of
> argument) reading that file from /tmp became unbearably slow.
>
> While investigating this, we came up with a test scenario that
> consistantly reproduced this behavior. The behavior is that if you
> have a system with 4gb of memory, and create a 1gb file in /tmp, and a
> 1gb file in /var/tmp, and then you start 2 processes each with an rss
> of about 1gb, your reads from /tmp get very... very..... slow. The
> file in /tmp was maxing out at about 6mb/sec read, with a typical read
> speed of about 2.5mb/sec as measured by iostat. The file from /var/tmp
> reads about 50mb/sec.
>
> All the large processes do is keep scanning their active memory in
> this loop:
> for(;;) {
> for (int i=0; i < nints; i++) {
> buf[i]++;
> }
> }
>
> We've found that using a similar scenario with 3 of these processes,
> one will swap out, an when killing the most active one, the swap in
> happens again at aound 2.5mb/sec.
>
> This makes /tmp pretty bad in most scenarios, but what's stunning is
> how swap behaves so slowly when paging a program back in.
>
> Does anyone know what is going on here, does this happen in nevada,
> and what we can do about this? We are persuing this with sun support
> but I thought this was a topic of broader interest.
>
> Thanks,
>
> -Peter
>
> --
> The 5 year plan:
> In five years we'll make up another plan.
> Or just re-use this one.
>
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