On Wed, 20 Apr 2011, Andrew Hume wrote:
i know, i know. this is an old chestnut.
we used to have swap 2-3x main memory,
but nowadays the wisdom is that that old rule
is no longer applicable. (this is on RHE5.)
so here i am, with a 128GB memory system with 16GB of swap.
and here i am, killing the system by running it out of swap.
my observation is that if i have large memory, i will use it.
(to say nothing of memory leaks etc.)
and if i have a few multiple large memory processes,
why wouldn't i want swap sized at 2-3x memory?
take a look back at the thread that started 'Why Do Linux Admins Seem To
Be So Much More Involved in the Community?' right where it morphed into
'swap needed was: Why Do Linux Admins Seem To Be So Much More Involved in
the Community?' for a fairly detailed discussion on swap (about the
beginning of Feb) right as the thread forked I did a fairly detailed
writeup of the history of swap requirements.
short version of the current situation (where you are not using
hibernation)
which do you want
a box crawling at 1/1000 it's speed (or less) because it's swapping
continuously
or
a box that crashes and restarts but operates at full speed otherwise
foe me, the first case is just as dead as the second case, but harder to
recover from (because it's so hard to get on to the box to tell it to
shutdown)
if you know that you have a memory leak and that the memory is not going
to be ever accessed again, then you can use swap space without slowing
down very much (you swap pages out but never swap them back in). I haven't
personally seen this case, but it is possible.
I never set swap >2g on my servers, and that's probably overkill.
David Lang
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