> From: "siddiq@xxxxxxx" <siddiq@xxxxxxx>
>
> On Sep 27, 2010, at 2:09 PM, Jan Steinman wrote:
>
>> On the Mac, tweaking any sort of memory setting in an application's
>> preferences has no effect, because everything is aggressively cached in RAM.
>
> Then why does that option even exist? (CS4 for OS X)
Good question! It would be interesting to get some empirical data. Have you
actually noticed any difference in twiddling with it? I haven't, but I may have
"expectation bias."
To do a reasonable empirical test, you'd need to re-boot and delete all the
caches before doing a test. You can't just reboot by itself, because Apple
stuffs a lot of state into temp caches that communicate between restarts.
Or make sure you do it three or more times, and throw out the outliers and
average the other measurements. Even then, I'll bet a litre of fresh goat milk
that the results are no better than random. (You have to come here to collect
the bet... :-)
"apropos memory" gives some interesting pages. You could try "vmmap -resident
PID" (where "PID" is the process ID of Photoshop, which you can see via "ps aux
| fgrep Photoshop". That will show you all Photoshop's memory allocations.
As far as I know, Photoshop does not run as root, and in Real Computers(TM),
you need to be root to lock down physical memory. Anything else that they're
doing is *probably* making things worse, by second guessing the OS memory
management. For example, if changing this setting causes Photoshop to request a
certain amount of memory that is not available, it will cause something else to
be swapped out to virtual memory -- possibly even some part of the Photoshop
process itself.
I suppose they could be querying how much physical memory is available, then
allocating a buffer pool that is some fraction of that, but such queries are at
best a transient snapshot of the physical memory allocation, and likely to be
wildly off in the next few tens of milliseconds.
Label me "dubious," but (like Philip K. Dick, below) willing to be
enlightened...
----------------
Reality is that which, when you stop believing in it, doesn't go away. --
Philip K. Dick
:::: Jan Steinman, EcoReality Co-op ::::
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