Re: Swap space question

First off, please turn off the HTML in eamil. Thank you.

On Sat, Sep 30, 2006 at 04:19:08PM +0300, nicolas angel wrote:

Hi, i would to ask something about swap space:
i quote from the book "How Linux WorksWhat Every Super-User Should Know"
"Reserve two to five times as much disk space as you have real memory for
swap. It doesn't make sense to go any lower, because you may actually risk
running out of memory. If you go higher and actually intend to use all of
this swap space, you will likely suffer serious performance problems because
the system will spend all of its time swapping (a condition known as
thrashing). "
i can't understand why if create a really big swap partition i will have a
performance decrease????It seems to me
that in the worst case scenario, i will be throwing disk space [because the
system will never use the swap partition if it doesn't need it......why this
would have a negative impact on the system......]
thanks in advance,
Nicolas Ang


The key to it is the conditions: "If you go higher [than four times
physical RAM] and actually intend to use all of this swap space,..."
It is how much swap space you use, not how much you have, that is
critical. The more swap space you have in use, the higher the
likelihood that a given page is in swap space rather than in physical
memory when needed, so the more the disk drive moves to get to swapped
pages, so the slower things appear to run.

The solution is to have more physical memory.

The rule of thumb to which I am accustomed is to have twice as much
swap space as physical memory. Of late I have been pushing
that. However the fact that I can get away with it doesn't say much,
because I have so much physical memory that I use very little swap
space.

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