Re: How likely is memory fragmentation?

Subject: Re: How likely is memory fragmentation?
From: Scott Fraser <email@hidden>
Date: Thu, 1 Dec 2005 09:51:32 -0800
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On Dec 01, 2005, at 07:04 AM, Steve Baxter wrote:

VM takes care of memory management so that memory fragmentation isn't an issue like it used to be. As far as your code is concerned it can allocate whatever size block you need as long as there's enough remaining of your 4Gig virtual memory space to fill the request. However, long before you run out of memory VM is going to start swapping pages to disk and performance will suffer.
Assumptions are evil! A G5 can support up to 8GB (maybe even 16GB now) of RAM, you can quite easily exhaust a 32-bit address space without causing any paging at all (we ship all our G5 systems with at least 4GB for instance).

Address space fragmentation is a real problem for applications that are working with large datasets. We ended up with a scheme where we can release blocks from our address space but keep a mach handle to them using mach_make_memory_entry(). This means that they stay in the unified buffer cache (in RAM if possible), but no longer take up any of our address space. I'm happy to talk more about this if anyone is interested!

Large datasets is what I'm looking at (~5Gig total) with large amounts of computation on top. It sounds like fragmentation isn't an issue for "normal" programs, but can be a realistic possibility for those outlying cases.

Scott
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  >Re: How likely is memory fragmentation? (From: Steve Baxter <email@hidden>)




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References:
	>Re: How likely is memory fragmentation? (From: Steve Baxter <email@hidden>)