paging

Considering Linux and 32 bit x86 arch there is 3:1 divide of the accessible 4GB address space. The user space is allocated 0-3 Gb while 3-4 Gb is allocated to kernel. How does a virtual address that is greater than 3Gb and hence lies into the kernel address space is transformed to the physical address? Does page tables would come into picture? There is some information in Mel Gorman's book Understanding the Linux Virtual Memory Manager . The short answer: Yes, the kernel sets up page tables to translate physical address 0 to virtual address 3 GiB. (Section 3.7.1). This includes the physical

I can't understand the answer to this question: Consider an OS using one level of paging with TLB registers. If the page fault rate is 10% and dirty pages should be reloaded when needed, calculate the effective access time if: TLB Lookup = 20 ns TLB Hit ratio = 80% Memory access time = 75 ns Swap page time = 500,000 ns 50% of pages are dirty. Answer: T = 0.8(TLB+MEM) + 0.2 ( 0.9[TLB+MEM+MEM] + 0.1[TLB+MEM + 0.5(Disk) + 0.5(2Disk+MEM)] ) = 15,110 ns Can you explain why? In this context "effective" time means "expected" or "average" time. So you take the times it takes to access the page in the

So I'm in a computer architecture class, and I guess I'm having a hard time differentiating between caching and pages. The only explanation I can come up with is that pages are the OS's way of tricking a program that it's doing all it's work in a specified region of memory, vs a cache memory is the hardware's way of tricking the OS that it's reading from one specified region of memory, when it's really not. Does the os direct the hardware that it needs a "new page" or is that taken care of by the os trying to read the address that is "out of range" of the current cache "page" (for lack of a

for tables with > 1,000,000 rows and possibly many many more ! haven't done any benchmarking myself so wanted to get the experts opinion. Looked at some articles on row_number() but it seems to have performance implications What are the other choices/alternatives ? We use row_number() to great effect and there hasn't really been any performance issues with it. The basic structure of our paginated queries looks like this: WITH result_set AS ( SELECT ROW_NUMBER() OVER (ORDER BY <ordering>) AS [row_number], x, y, z FROM table WHERE <search-clauses> ) SELECT * FROM result_set WHERE [row_number]

Most of the ASP.NET MVC paging solutions I have found by googling look like they get all rows from a database table in the form of a IEnumerable collection, perform some paging conversion on the IEnumerable collection, and then return the results to the view. I want to be able to page on the DB side but still have some paging class to do the page number calculations and HTML generation. Is there a solution out there that does this? Or are the ones i've been looking at do this, but i'm not seeing it because i'm looking at them wrong? here's what i've been looking at: http://blogs.taiga.nl

I am doing some paging in my application, returning 20 rows from the database at a time using PostgreSQL's standard OFFSET and LIMIT keywords. For instance, to get page 1 page: SELECT stuff FROM table WHERE condition ORDER BY stuff OFFSET 0 LIMIT 20 It is a requirement of the application that we also show to the user the total number of records. So, obviously, I can get the total by issuing a separate query: SELECT COUNT(*) FROM table WHERE condition But if there are a large number of rows then this is not an optimal solution. I notice that MySQL has a very useful function called FOUND_ROWS()

Prologue I am an operating system hobbyist, and my kernel runs on 80486+, and already supports virtual memory. Starting from 80386, the x86 processor family by Intel and various clones thereof has supported virtual memory with paging. It is well known that when the PG bit in CR0 is set, the processor uses virtual address translation. Then, the CR3 register points to the top-level page directory, that is the root for 2-4 levels of page table structures that map the virtual addresses to physical addresses. The processor does not consult these tables for each virtual address generated, instead

I found this example. Consider a system with a 32-bit logical address space. If the page size in such a system is 4 KB (2^12), then a page table may consist of up to 1 million entries (2^32/2^12). Assuming that each entry consists of 4 bytes , each process may need up to 4 MB of physical address space for the page table alone. What is the meaning of each entry consists of 4 bytes and why each process may need up to 4 MB of physical address space for the page table ? Matthew A page table is a table of conversions from virtual to physical addresses that the OS uses to artificially increase the