On Sep 26, 2009, at 12:53 PM, Bob Carls Dudney wrote:
>> It's my understanding OS X will use available RAM for a disk cache.
>> I can use up 32GB of RAM running Photoshop while Photoshop itself
>> only sees a fraction of that.
>
> I presume that's inactive memory. Worst example I've seen how poorly
> OS X manages VM. I presume that's same as or mostly heap L.W. Brown
> said the OS never clears.
No, no, no.... I hope that as much of it as possible is active memory.
The more work it's doing in RAM the better. If I've got a 200 or 300GB
swapfile while having any of my RAM used to store stuff that doesn't
change very often, that would be very very bad.
The folks at Adobe *claim* that having more RAM than Photoshop can
actually see is still beneficial because OS X uses the RAM as a disk
cache for Photoshop's swapfile operations. Adobe could be full of it,
but I don't know. When I upgraded the system from 10GB to 32GB the
performance increase on an 18 and a half minute operation was about
twenty seconds. Not all that impressive, but it was something. It's
not surprising at all that it wouldn't be a huge boost. I probably
should have found a test that involved the memory use near 12-15GB. I
suppose I still could, but I don't want to be yanking memory in and
out of the machine to tests.
I probably should. Seeing that OS X likes to gobble up 2.5GB of RAM at
startup, if Photoshop has most of 8GB allocated to it, then OS X is
probably using some swap at 10GB of RAM that it doesn't at 32GB. That
20 seconds could have come from OS overhead. The disk cache might be
worthless compared to Photoshop being able to address RAM in a 64-bit
space.
Not sure.
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Received on Sat Sep 26 18:57:49 2009
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