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Re: [SLUG] Increasing RAM


On Sunday 19 April 2009 10:00:03 slug-request@xxxxxxxxxxx wrote:
>  On Sunday 19 April 2009 00:16:35 slug-request@xxxxxxxxxxx wrote:
> >> I've decided to increase the RAM on my home CentOS server. As best I
> >> can recall, the accepted wisdom is to have SWAP approx.~ 2 x RAM. Or
> >> was that approx.~ 50% of RAM?
> >>
> >> Can someone point me in the direction of an explicit tutorial on how
> >> I might go about increasing SWAP without destroying data on my other
> >> partitions please?
> >>
> >> Or if I'm actually upping the RAM, should I just not worry about it?
> >>
> >> Info I'm guessing would be relevant;
> >
> > Of course this is cockamany, urban myth, etc and typically you
> > increase RAM and need even less swap than before
>
> Actually, back in the day this was a good and solid guide, both for
> performance and safety reasons.  Today, less so, but I don't think it is
> quite as laughable or untrue as you suggest.

From the days of my first system (PDP11, 100K RAM, 15MB disk) till today I 
cannot see why this opinion is held. I first encounted it as a RedHat 
recommendation. Pray wax lyrical ...

> > EXCEPT for 1 tragic circumstance: Never *suspend* unless you have as
> > much SWAP as RAM.
>
> You mean suspend to disk, not suspend to RAM, right?  Swap is irrelevant
> to the later, and the amount you need varies with which of the three
> implementations of the former you choose.
>
> However, all of them require as much swap as you have *active memory*,
> not as much as RAM — although, obviously, if you have no discardable
> pages[1] then you need the two to be equal.

If your active RAM is not equal to physical RAM then the systems is not doing 
ir right (your definition of active ram ?)

> > Suspend writes all RAM starting at the beginning of swap and over
> > everything along the way.
>
> No, it doesn't.  It uses the swap storage space just like the normal
> kernel, except for adding some private accounting information and a
> different header to make it possible to detect that it was used to
> suspend to disk.

OK it starts SOMEWHERE in swap then writes over everything. In any event I 
lost my home partition (root swap home)

> If it behaved as you describe[2] then it would corrupt memory on the way
> through as it overwrote swapped data (and, then, no one would ever
> report a successful suspend to disk. :)

I never use any suspend and clearly don't appreciate the fine detail, but how 
would this ever work

1G RAM
2G swap

VasttExtravagentApp using 1.9G of swap, then suspend-to-disk?

James