RE: Maximum useable swap in kernel 2.4

["Bodle, Donald E" <donald_bodle reyrey com>]

Well, I tried setting up 4 swap areas.  The first default 1GB is on sda, the
other 3 2GB are on sdb.  Still, /proc/meminfo shows only 3GB total/free at
the top, though it shows 7GB total/free at the bottom.

I was playing with make xconfig, and it has a selection for "maximum virtual
memory" that was limited to 3GB.  So, perhaps there is a kernel limit?  I
will use xconfig again and actually save the config file and see what its
setting for max virtual memory....

BTW, I'm still running a fairly vanilla 7.1 distribution, kernel 2.4.2-2.

So, what is the reality?  I may end up finding out only through exercise of
a system to fill up the swap.

Don

-----Original Message-----
From: Thomas Dodd [mailto:ted cypress com]
Sent: Thursday, November 15, 2001 4:20 PM
To: redhat-install-list redhat com
Subject: Re: Maximum useable swap in kernel 2.4




Bodle, Donald E wrote:

> I've been searching through the archives, reading the mkswap man page, and
> must be really thick-headed.
> 
> What is the maximum amount of swap space the kernel can use?
> 
> I've seen notes on 2GB swap area limits, and no more than 8 swap areas.  I
> don't want to debate whether or not our choice of 2x memory is a good one,
> at least not at this point.  What I want to know is, if I set up - in one
or
> more swap areas - 8GB of swap for a system with 4GB of memory, can the
> kernel ever use that 8GB of swap?  I certainly don't want to waste the
disk
> space if it's not useable, and it will greatly simplify my post-install
> script for adding swap based on memory.


No single swap area (file or partition) can be over 2 GB.
and looking at the kernel source for 2.4.9-13
in include/linux/swap.h I think the max is
now 32  < #define MAX_SWAPFILES 32 >

I created 10 small (1M) swapfiles with dd and mkswap.
swapon activated all of them. and 'swapon -s' showed
the 10 file and my normal 256M partition as
active.

The test shows that much worked (11 swap arears active)

So the space is usable (2 GB of each partition anyway).
But 8GB would likely be a waste. Depends on what the work load
is, but I hav 256MB and never use more than a few meg.

		-Thomas






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