[TUHS] signals and blocked in I/O

Arthur Krewat krewat at kilonet.net
Tue Dec 5 02:58:20 AEST 2017


I've had some strange experiences with Solaris 11, where if I didn't 
have enough swap, I'd get OOM issues with Oracle databases (SGA) on 
startup and other various things.

While Oracle docs say it's OK to have a small swap area if you have 
plenty of RAM, I've experienced the exact opposite. If the ZFS arc is 
large (and it always is), and something needs memory, if there isn't 
enough swap to "guarantee" the allocation, the allocation will fail. 
(Disregarding the fact that the ZFS arc can be tuned, and now Solaris 
11.3 has an even better setting, user_reserve_hint_pct). It won't wait 
to flush out ZFS arc to make room, it'll just fail outright.

With a huge swap area that's at least half the size of RAM (in boxes 
that range from 96GB to 256GB), even though it'll never touch the swap, 
it works just fine.

Now, I understand your issue is with BSD, but if it's ZFS, perhaps 
there's something not-so-different about the two environments.

$.02

On 12/4/2017 11:36 AM, arnold at skeeve.com wrote:
> Larry McVoy <lm at mcvoy.com> wrote:
>
>> So I have 10 processes, they all run until the system starts to
>> thrash, then they are all in wait mode for memory but there isn't
>> any (and there is no swap configured).
> Um, pardon me for asking the obvious question, but why not just configure
> a few gigs of swap to give the OS some breathing room?
>
> Most modern systems let you use a regular old file in the filesystem
> for swap space, instead of having to repartition your disk and using a
> dedicated partition. I'd be suprised if your *BSD box didn't let you do
> that too.  It's a little slower, but a gazillion times more convenient.
>
> Just a thought,
>
> Arnold
>



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