SuperFetch is something all operating systems should have. I didn't buy 4GB of top-notch RAM just to have it sit there doing nothing during times of low memory requirements. SuperFetch makes my applications load faster, which is really important to me - I come from a BeOS world, and I like it when my applications load instantly.
SuperFetch' design makes sure that it does not impact the system negatively, but only makes the system smoother. Because it runs at a low-priority, its cache doesn't take away memory from the applications you're running.
http://www.osnews.com/story/21471/SuperFetch_How_it_Works_Myths
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Q: You didn't mention Address Space Layout Randomization (ASLR) and if it impacts Page Sharing, does it?
A: I didn't cover ASLR because the blog was pretty long already, but since you asked...
Yes, ASLR does impact the Page Sharing efficacy, but first a quick description of ASLR from a
TechNet article written by Mark Russinovich
:
The Windows Address Space Layout Randomization (ASLR) feature makes it more difficult for malware to know where APIs are located by loading system DLLs and executables at a different location every time the system boots. Early in the boot process, the Memory Manager picks a random DLL image-load bias from one of 256 64KB-aligned addresses in the 16MB region at the top of the user-mode address space. As DLLs that have the new dynamic-relocation flag in their image header load into a process, the Memory Manager packs them into memory starting at the image-load bias address and working its way down.
Mark continues with...
In addition, ASLR's relocation strategy has the secondary benefit that address spaces are more tightly packed than on previous versions of Windows, creating larger regions of free memory for contiguous memory allocations, reducing the number of page tables the Memory Manager allocates to keep track of address-space layout, and minimizing Translation Lookaside Buffer (TLB) misses.
Today, the impact of ASLR on Page Sharing is relatively low ~10% compared to Large Memory Pages and SuperFetch, but it is indeed another factor that impacts Page Sharing efficacy. Moreover, that's not to say that future improvements in ASLR won't impact Page Sharing efficacy further.
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Q: You mention that Large Memory Page Support in included in the last few generations of Opterons and Intel has added support in the new "Nehalem" processors. Do you mean older Intel x86/x64 do not support Large Memory Pages?
A: 5/6/2010: CORRECTION: Actually, older x86/x64 processors do support Large Memory Pages going back many generations. However, 32-bit systems generally didn't support generous amounts of memory (most maxed out at 4 GB which is a small fraction of what 64-bit systems support) so support for Large Memory Pages wasn't as crucial as it is now with 64-bit servers being the norm.
In my next blog we'll discuss Second Level Paging...
Jeff Woolsey
Principal Group Program Manager
Windows Server, Virtualization
P.S. Here are the links to all of the posts in this blog series:
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