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Date:      Thu, 5 Dec 2002 14:53:46 +0300 (MSK)
From:      Varshavchick Alexander <alex@metrocom.ru>
To:        Terry Lambert <tlambert2@mindspring.com>
Cc:        <freebsd-questions@FreeBSD.ORG>, <freebsd-hackers@FreeBSD.ORG>
Subject:   Re: maxusers and random system freezes
Message-ID:  <Pine.GSO.4.33.0212051438100.7912-100000@apache.metrocom.ru>
In-Reply-To: <3DEF37AF.182DD85@mindspring.com>

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On Thu, 5 Dec 2002, Terry Lambert wrote:

...

> > Are you talking primarily about SHMMAXPGS=262144 option here? Then may be
> > it'll be oevrall better to reduce it and make KVA space 2G, to leave more
> > room for user address space?
>
> That's the one I was referring to, yes, but you didn't post your
> whole config (please do *NOT* post it; I can't spend the time on
> going over it line by line).
>

All other config options are pretty much like the default ones.

> Tuning is a skill; it can be plotted out as a cookbook recipe,
> but it takes a lot of work to do that, and no one has volunteered.
>
> Basically, to write out a cookbook, you have to know where every
> byte of memory is going in the kernel, and what tunables impact
> each other, and how they are related.
>
> Once you know that, you could easily write a program to kick out
> a configuration file for various usages, or even modify the code
> to auto-tune itself (everything by KVA space, which impacts the
> base address that the kernel gets linked to... unless you compile
> the entire kernel PIC, which I do not recommend).  But knowing
> the information is hard.  I know it for 4.3 and 4.4.
>

You're right, expecially for getting an _ideally_ tuned kernel.  However
in a real life, a specialist cannot have an absolute knowledge about _all_
server and other issues, so practical solutions are being looked for in
items which can arise. Of cause, no one is arguing that a basic knowledge
is needed and required.

...

> If you are having system freeses at random, and you want to fix
> them instead of living with them, some experimentation is going
> to be inevitable.  I don't know enough about your installation
> to be able to give you a kernel config file to use that will
> magically fix all your current issues for you, and prevent future
> issues from coming up.  That's going to have to be up to you.
>
>

Surely, I'm just trying to reduce the experimental attempts as much as
possible and to rise the chances of success for each new configuration
version.

...

> > No, the swap is very slightly used on this server, and the total swap
> > size is 2G.
>
> It doesn't matter.  The amount of swap the kernel allocates page
> tables for is based on the amount of physical RAM in the machine.
> You pay for the page tables whether you use them or not, for swap,
> for the kernel, and for any memory which you permit to be allocated
> at interrupt time, plus any allocations that occur after you are up
> and running, until you run out of physical RAM.
>
> This is "one of those things" you just have to know about how
> the kernel uses virtual memory, if you are going to be a skilled
> kernel tuner.
>
>
> As a rule, swap should be at least physical memory size + 64K on
> any system that you need to be able to get a system dump from,
> since it needs to dump physical RAM.  If you are not worried about
> the machine falling over, then you can ignore that.
>
> Note that "man tuning" suggests 2* physical RAM for swap.
>
> PS: I am going to be out of touch (able to download, but not
> send email) for the next couple of days... up to a week.  If you
> have more questions, and they can't wait, you will need to ask
> someone else.
>

Thank you for all your advices, they've already helped a bit. Have luck in
your trip or elsewhere.

-----
Alex


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