Re: top(1) and the meaning of columns

Tim Post <tim.post@xxxxxxxxxxxxxxx> writes:
I'm not discounting the RES/SHR columns because they are indeed
interesting, but not entirely useful and as someone pointed out .. a bit
cryptic.

RES (aka RSS) is actually extremely important: if the sum of all
programs' RSS exceeds your RAM size, your system will thrash, and
thrashing is not good.

By contrast, as long as you have swap space available it's generally not
a problem (and in fact rather common) for the sum of all VIRT (- SHARE)
to exceed RAM size.

Once the sum of all VIRT - SHARE (more or less) exceeds RAM + swap size,
of course, then the kernel starts to kill programs. Usually this
happens only after your system began to thrash a long time ago, so in
many cases you have a chance to manually kill something before you reach
that point.

[Strictly speaking, RSS is only an estimate of a somewhat nebulous
concept, but that's the general idea.]

-Miles

--
The car has become... an article of dress without which we feel uncertain,
unclad, and incomplete. [Marshall McLuhan, Understanding Media, 1964]


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