Skip to main content

Page Size Extension

Page Size Extension

From Wikipedia
In computingPage Size Extension (PSE) refers to a feature of x86 processors that allows for pages larger than the traditional 4 KiB size. It was introduced in the originalPentium processor, but it was only publicly documented by Intel with the release of the Pentium Pro.[1] The CPUID instruction can be used to identify the availability of PSE on x86CPUs.[2]

Motivation[edit]

Imagine the following scenario. An application program requests a 1 MiB memory block. In order to fulfill this request, an operating system that supports paging and that is running on older x86 CPUs will have to allocate 256 pages of 4 KiB each. An overhead of 1 KiB of memory is required for maintaining page directories and page tables.
When accessing this 1 MiB memory, each of the 256 page entries would be cached in the TLB (a cache that remembers virtual address to physical address translations for faster lookup on subsequent memory requests). Cluttering the TLB is possibly one of the largest disadvantages of having several page entries for what could have been allocated in one single memory block. If the TLB gets filled, then a TLB entry would have to be freed, the page directory and page tables would have to be “walked” in memory, and finally, the memory would be accessed and the new entry would be brought into the TLB. This is a severe performance penalty and it is possibly the largest motivation for augmenting the x86 architecture with larger page sizes.
The PSE allows for page sizes of 4 MiB to exist along with 4 KiB pages. The 1 MiB request described previously would easily be fulfilled with a single 4 MiB page, and it would require only one TLB entry. However, the disadvantage of using larger page sizes is internal fragmentation.

Operation[edit]

“traditional” 4 KiB paging
4 MiB paging using PSE
In traditional 32-bit protected mode, x86 processors use a two-level page translation scheme, where the control register CR3 points to a single 4 KiB long page directory, which is divided into 1024 x 4 byte entries that point to 4 KiB long page tables, similarly consisting of 1024 x 4 byte entries pointing to 4 KiB long pages.
Enabling PSE (by setting bit 4, PSE, of the system register CR4) changes this scheme. The entries in the page directory have an additional flag, in bit 7, named PS (for Page Size). This flag was ignored without PSE, but now, the page directory entry with PS set to 1 does not point to a page table, but to a single large 4 MiB page. The page directory entry with PS set to 0 behaves as without PSE.

PSE-36[edit]

Main article: PSE-36
If newer PSE-36 capability is available on the CPU, as checked using the CPUID instruction, then 4 more bits, in addition to normal 10 bits, are used inside a page directory entry pointing to a large page. This allows a large page to be located in 36 bit address space.

PAE[edit]

If PSE is used together with Physical Address Extension (PAE) the size of the pages is reduced from 4 MiB to 2 MiB.

Comments

Popular posts from this blog

fix idm integration on chrome

Chrome Browser Integration I do not see IDM extension in Chrome extensions list. How can I install it?  How to configure IDM extension for Chrome? Please note that all IDM extensions that can be found in Google Store are fake and should not be used. You need to install IDM extension manually from IDM installation folder. Read in step 2 how to do it . 1. Please update IDM to the latest version by using  "IDM Help->Check for updates..."  menu item 2.  I don't see  "IDM Integration module"  extension in the list of extensions in  Chrome . How can I install it? Press on  Chrome  menu ( arrow 1  on the image), select  "Settings"  menu item ( arrow 2  on the image) and then select  "Extensions"  tab ( arrow 3  on the image). After this open IDM installation folder ( "C:\Program Files (x86)\Internet Download Manager"  by default,  arrow 4  on the image) and drag and drop  "IDMGCExt.crx"  ( arrow 5  on the image) file int

Hidden Wiki

Welcome to The Hidden Wiki New hidden wiki url 2015 http://zqktlwi4fecvo6ri.onion Add it to bookmarks and spread it!!! Editor's picks Bored? Pick a random page from the article index and replace one of these slots with it. The Matrix - Very nice to read. How to Exit the Matrix - Learn how to Protect yourself and your rights, online and off. Verifying PGP signatures - A short and simple how-to guide. In Praise Of Hawala - Anonymous informal value transfer system. Volunteer Here are five different things that you can help us out with. Plunder other hidden service lists for links and place them here! File the SnapBBSIndex links wherever they go. Set external links to HTTPS where available, good certificate, and same content. Care to start recording onionland's history? Check out Onionland's Museum Perform Dead Services Duties. Introduction Points Ahmia.fi - Clearnet search engine for Tor Hidden Services (allows you

Explainer: The nico-teen brain

Explainer: The nico-teen brain The adolescent brain is especially vulnerable to the addictive effects of nicotine BY  TERESA SHIPLEY FELDHAUSEN   7:00AM, AUGUST 19, 2015 Nicotine (black triangle towards center left) tricks the nerve cell (neuron) into sending a message to release more dopamine (yellow dots). Those molecules enter the space (synapse) between one nerve cell and the next. When they get picked up by neighboring cells, this gives users a feel-good high. It also creates the risk of addiction and other health problems.  EMail  Print  Twitter  Facebook  Reddit  Google+ NATIONAL INSTITUTE ON DRUG ABUSE, ADAPTED BY J. HIRSHFELD Nicotine is the addictive chemical in tobacco smoke and e-cigarette vapors. And doctors say the teenage brain is no place for it to end up. Nicotine can reach the brain within seven seconds of puffing on a cigar, hookah, cigarette or electronic cigarette. The area of the brain responsible f