mmap() only version of ptmalloc3 and how to benchmark it

[Valdis.Kletnieks at vt.edu]

On Wed, 28 May 2014 12:37:48 -0700, Aaditya Gavandalkar said:
> So considering all these points, is it of any advantage to save on swapping
> time while having all those extra overheads.

The short answer is "it depends".  The long answer is "it depends".

Do you have actual numbers that show a saving in swapping time? If so,
how much of a reduction?  Is there a difference if you're only slightly
into swap (maybe 50M or so), or heavily into swap (multiple gigabytes) but
most swap-resident pages are old and inactive (for instance, your Firefox
image when you come in in the morning, after it's been forced out to swap
by a 2AM backup), or heavily into swap and high activity (in other words,
if your system is thrashing)?

Which is more important, saving on swapping time because you have an
elapsed-time issue (for instance, a backup service that isn't making an
allotted time window), or the overhead (if your server is already running at
90% CPU)?

And the first question that my boss is going to ask me in this situation is
"Why doesn't a server that's running a critical application have enough RAM
installed so that you don't ever hit swap in the first place?"

(You want to see painful?  An SGI UV system that has 2.7T of RAM (*not*
a typo) and it's swapping.  Ouch doesn't begin to describe it...)


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