Automatic allocation of swap
I have just installed another system, and took the time to try to
familiarise myself with the partitioning tool.
I was running a 2.6 kernel, and the install kernel's date is Jul 29 06:24.
The install target was a Pentium II, 350 Mhz, 64 Mb RAM and 3.2 Gbytes
It seemed to me that the setup chosen for "multiuser" was entirely
impractical. Unfortunately, I was more interested in testing other
aspects, so I just wiped that one and tried some others.
One aspect of that configuration I do recall.
It allocate about 192 Mbytes of swap partition, right at the edge of the
I have never thought swap partitions on single-disk systems are a good
idea, and here is why.
If there is little swapping, then any perfoemance benefit is immaterial.
If swapping is severe (the system is thrashing), there is no good
alternative to more RAM. RAM is cheap.
That aside, the position of the swap area (in the d-i configuraton as
in most others) ensures the swap area is far from the data, ensuring
that operations such a opening an OOo document will send the disk heads
seeking far, back and forth, back and forth, back and forth, across
much, maybe most, of the disk surface.
In between, of course, is inbetween: bad sometimes, not so bad at others.
In contrast, if I create a swap file, then it there is some prospect it
will be near at least some of the data I need to read.
The common Rule of Thumb (ROT) has the appropriate size of swap being
twice the amount of RAM installed (not three times!).
My own experience is that, mostly, system performance is pretty terrible
before it's used all the swap area. The sole counterexample I can think
of is using rsync to do backups. rsync can use enormous amounts of
virtual memory backing up whole disks, but its working set remains modest.
The stupidity of this ROT is illustrated when adding more RAM. If my
system is working moderately well with xMbytes of RAM and I, noting that
RAM is cheaper than formerly, decide to add 2x Mbytes of RAM, should I
also treble the amount of swap? Of course not, I may well decide I have
better uses for that disk space.
Either way, the amount of swap is wrong, and recovering or enlarging the
amount of swap in a swap partition is not a trivial undertaking.
Finally, the point that I installed a 2.6 kernel is an important one.
One of the changes I note in the new kernel is that there is no
performance benefit to using swap partitions.
I recommend that, if there is one disk, a swap file be created rather
than a swap partition.
And, if /home is a separate partition, then it should be on that
partition. That is where most I/O activity is likely to be on
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