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Comprehensive Guide to the Windows Paging File
busfahrer writes "Adrian's Rojak Pot has a nice article about the internals of the Windows paging file. It explains what a paging file is and lists the differences between a swapfile and a paging file. But first and foremost, a large part of the article deals with the various methods of optimizing the Windows paging file, thus yielding a notable performance gain for people who are not overly blessed with RAM."
One of the biggest performance helps is to keep the paging file from being fragmented, and I'm not talking about three or four fragments.
I've come across workstations where the paging file is in thousands of fragments. This happens when someone messes with the settings. For instance, they might increase the size of the paging file thinking it'll help to have more. Normally, it's not a bad idea to increase it but if the drive is heavily fragmented, Windows dutifully uses the fragments for the new space.
The only way to fix it is to completely delete (deactivate) the page file, then do a defrag, then re-create the page file (several reboots involved).
That's probably the best way to tune the page file. There, I saved you from having to take the time to read the article.
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Would Mr. File please pick up one of the white courtesy phones? Your OS needs to talk to you.
They might want to adjust the paging file on their web server a bit...
Given the speed of the slashdotting, I'd say he needs to add more ram to his box, and stop relying on the paging file for speed...
Online Starcraft RPG? At
Dietary fiber is like asynchronous IO-- Non-blocking!
http://www.bysoft.com/freeram.asp
A free application that you can use to 'pre-page' out pages right before loading up your application. What it does is hog as much RAM as much as it can, forcing the OS to page out any unnessecary applications.
I've seen the standard Explorer + lsass + cwrss + all the svchosts memory footprint go from 80-ish megs to 20. Running this before your game will allow quick load-times and quicker performance.
... for people who are not overly blessed with RAM.
You mean those who's PHBs said the "minimum" requirements were good enough.
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As far as I know it doesn't...
Here is some more info about paging and swapping under unix
AFAIK a page is an group of memory addresses that are being changed/addressed at the same time.
But I could be mistaken
It's 44 Pages!! I mean heck, the average /. doesn't read one page news stories, but a 44 Page Article!? Not in this lifetime.
Your hair look like poop, Bob! - Wanker.
The site is so slashdotted that it took forever to load the first page which basically has nothing but useless history of swap files on it. Even the mirrordot doesn't appear to be working. Anyway, one sentence on that first page made me no longer interested in reading the article:
Whenever the operating system has enough memory, it doesn't usually use virtual memory.
This flies in the face of real world experience. You can have 4 gigs of RAM and nothing but Windows 2000 running and your OS will still use the swap file frequently. Don't believe me? Run Performance Monitor and monitor Memory, Pages/Sec and just click on a few things and you'll see that I'm correct.
I'm a big tall mofo.
The solution they came up with was to use some space on the hard disk as extra RAM. Although the hard disk is much slower than RAM, it is also much cheaper and users always have a lot more hard disk space than RAM. So, Windows was designed to create this pseudo-RAM or in Microsoft's terms - Virtual Memory, to make up for the shortfall in RAM when running memory-intensive programs.
Amazing how they manage to turn everything around as though Microsoft invented the world of computing...
Virtual memory, the term and the implementation have been around long before Microsoft came into existence.
There's a good reason why people don't write about VM systems often; the combination of writing skill and the ability to understand modern VM is extremely rare.
Take most, if not all, of what the article discusses with a large grain of salt. Everything, from his history (did Microsoft invent demand paging? Hardly) to his terminology is flawed.
Just reading the first 40 comments or so here reveals that VM remains one of those "black magic" areas, where reason is overcome by superstition and people will assert the most ridiculous, irrational and unsupportable things. Regrettably, the contents of this article do nothing to improve the situation.
= Mike
SysInternals (who make some of the best freeware available for Windows) has PageDefrag. It defrags your registry hives and pagefile at boot, before Windows loads. Very slick program and free to boot.
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Well, since you've had four incorrect and or unhelpful responses so far, let me shed some light:
/proc/sys/vm/swappiness. This can be set on a value from 0 (try to never swap) to 100 (agressively write out pages to disk). By default, it is set to 60. To change the swappiness, say, to 40:
Linux only has a paging file (it's still called swap space though). This can either be a hard drive partition, or a regular file.
To make it as a regular file:
dd if=/dev/zero of=some_file bs=1M count=however_big_you_need_it_in_megs
Then:
mkswap some_file
Then:
swapon some_file
You don't need to reboot, and you can add/remove these files at will using swapon/swapoff and the normal filesystem tools.
The 'swappiness' of Linux can also be tuned: since kernel 2.6.0 there has been a proc file
echo 40 >/proc/sys/vm/swappiness
Most 2.6-based distros have some GUI tool that can tweak parameters like this (Fedora certainly does).
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Well, they tried, but I think they really missed some very commonly-held misconceptions.
I've just finished a project involving reconstructing process images from physical memory, including pages from swap, if available, so I've got a pretty good understanding of this stuff at a very low level.
Misconception 1: Swap-file usage = performance degradation
Yes, it is slower (usually by 3 orders of magnitude, not 1) to access a page (frequently 4K) from disk instead of memory. HOWEVER, effiency dictates that all available RAM be utilized as soon as possible.
For example, in addition to running processes, we also use volatile memory storage to cache file data. Clearly, we want to cache as much as possible. Page replacement policies then become important to determine how much swap space to use. But usually it is much greater than 0, because we've got process image pages that are less frequently used than a lot of file cache pages. So we've gotta remember that data, but we don't wanna waste fast RAM on it.
In other words, isn't it great that we can swap out pages from an unused process to make room for frequently accessed file data? Regardless of how much memory we have, that's a Good Thing.
Misconception 2: Virtual memory = disk space
Virtual memory is a mechanism for translating program-visible addresses to arbitrary storage locations transparently. This doesn't necessarily mean that disk space is used for swapping memory, it means, for example, that 5 processes can simultaneously be accessing address 0x5000, but the actual storage location is different for each. If the system (usually the page address translation facility on the CPU) determines that this address isn't at some location in volatile storage, it will bring in that memory from swap space and possible page out some other data. This is what the article is generally talking about.
I've seen some other questions about pages. There are a couple reasons for treating memory in page-size chunks, where a page is usually in the 1-8k range (4k for x86). First, the page address translation stuff needs to keep data on translations. It must do this in > 1 byte chunks, since keeping translation data on every byte would require way too much storage. Disk I/O and other I/O is frequently done on page-by-page basis for that reason as well as for the sake of performance.
Well, I rambled enough. Just wanted to clear a couple things up.
I found this link to the article: Swapfile_Optimization
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Putting http://text.burstnet.com/* into adblock makes for a slightly less annoying experience, but there's also the fact that it's 44 freaking pages long. Probably getting paid by the site hit or something.
Do yourself a favor, give this content-lite article a miss. Make a small partition with ntfsresize, put a fixed pagefile on that partition alone. Works on every single version of windows and it's zero maintenance. Tah-dah.
I am no longer wasting my time with slashdot
It is always amusing to me to read how M$ "invented" technologies that were in common use by other operating systems while Bill Gates was still wearing diapers. Both paging and swapping were used on IBM mainframes dating back to the mid 1960's. What windoze (and linux for that matter) could REALLY use is the ability to deterministically dedicate portions of system resources to particular processes.
Back when a 1 MIP, 1MB machine cost $1M, operators became highly skilled at managing workloads. Today everyone just throws oodles of RAM and disk at servers and lets the chips fall where they may , so to speak. It wouldn't be a bad idea to actually put a little thought into matching workloads with machine resources, and pro-actively matching them up by deliberate choice(For example - our company is running a prime-time ad at 9pm that features our URL, maybe that's a good time to shut down the normal file backup that happens then). Chaos theory is not always a good load balancer. But what am I saying, that's as outrageous as asking kids to put their money in the bank instead of buying video games...
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I've mentioned it elsewhere already. But try PageDefrag and Buzzsaw.
The first one will defragment your Windows pagefile on each boot. And Buzzsaw will defragment recently accessed files in the background, much less intrusive than Diskkeeper. Both are freeware tools.
To change the swappiness, say, to 40:
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Rockeringly on, dude!
HA! I just wasted some of your bandwidth with a frivolous sig!
For example, even under Windows 3.1, the swap file only swapped in chunks of 4/8k. It's just that, on machines that were memory-poor (like we all were way back when), most users had their boxes configured with a 3/1 ratio of swap to real ram, and most of their free real ram then ended up being used to manage the swap file. 2/1 was the sweet spot.
The DOS Shell program, on the other hand, worked by swapping out whole processes, allowing DOS 5.0 and up to appear to multitask.
Pick up a copy of any decent assembler manual for the 2/386 from the early '90s, look for the instructions for swapping pages into ram. It's a hardware function. On a page fault, the cpu then goes through a look-aside buffer (8k worth of pointers each, IIRC, local and global), and then you can map pages of ram in/out as required. Just don't triple-fault, as the cpu would then go out of "enhanced" mode and/or reboot.
Must be a REALLY SLOW day for this to be "news".
Who needs a page file when you have a 10.00 GHz AMD Athlon, a 2000 MB DIMM, and a 30000 GB IDE Hard Disk http://www.amazon.com/exec/obidos/tg/detail/-/B000 22ACYK
I quote from a review:
"I was a little skeptical at first on how this thing would perform. However, when I installed and run the Seti@home program it started instantly finding alien signals, which where corrected, cleaned up and translated.
I am now listening and talking to the supreme galactic defense minister about Earths surrender. Apparently this computer is not only tapping into the sun for power but also into the mysterious dark energy and tearing the universe apart. Just comes to show how bugs always show up in technology when you least expect it."