Memory Overhead

Question

What is memory overhead? Is it's size same as size of page table for the process?

Comments

yes ..memory overhead refer to the Page table size for given process

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its page table + internal fragmentation

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@Vegeta

Any example?

any math came where internal frag also added?

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The reason could be this,

Suppose process size = 12KB and page size = 1KB then we can divide the process into 12 pages and there is no wastage here, So in the best case, page wastage will be 0 and suppose if our process size is 12KB+1 Byte(extra) then in this case, page wastage will be equal to 1 page because here we will need total 13 pages So here page wastage  would be p. (worst case)

So on average page wastage  = (0+p)/2 =p/2

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we can not use the word internal fragmentation here, because internal fragmentation is already removed in dynamic partitioning technique, but in order to avoid external fragmentation, they invented paging which completely avoids external fragmentation too.

Note: if there is no external fragmentation, then there can not be internal fragmentation.

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Bro there is internal fragmentation in paging and it is memory overhead if we don't take page size correctly.

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overhead means what is the extra, that you should have for your requirement.

coming to paging, your requirement is finding a word ==> requires finding a page ==> finding page requires a page table.

generally, we have pages mandatory, but by going with paging we should store page tables also.

therefore memory overhead w.r.to paging = size of page tables.

 

@Vegeta

Fragmentation is wastage but not overhead.

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Yeah, you may be right.

What my thought is Memory overhead(in term of space) is the amount of main memory is wasted, which we could use for the process to fit in that memory part.

As the page table should present in main memory, which we use to find the frame no. So the size of the page table is total wastage for main memory space, hence memory overhead(in term of space).

But if we don't take page size correctly, then there could be internal fragmentation. Suppose if our process size is 12KB+1 Byte(extra) and page size = 1KB then, in this case, We have to give 1KB page to 1B of the process, and when this page goes in main memory we have total wastage of (1KB - 1B) of main memory space which we could use, this is also wastage and it is also memory overhead(in term of space).

But if see the overhead(in term of time) the whole paging process is overhead.

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paging contains internal fragmentation, 

So, page table also contain internal fragmentation

See here https://gateoverflow.in/916/gate2003-26

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@srestha,mam

page table also contain internal fragmentation

it may or may not page table contains internal fragmentation...

But i am not getting what is the relation between this question and this point.

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that means overhead also contain internal frag

isnot it?

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the overhead may contain internal fragmentation of page table... but internal fragmentation due to page is not considered as overhead.

 

let you and your family attending a wedding party, you are totally 26 people and you arrange care takers for every 4 people. and you book cabs for all to reach function hall, ( let each cab allows 3 people only. )

==> 26 people ==> 26/3 = 9 cabs required. ( but the 9th one have internal fragmentation. )

==> 26 people ==> 26/4 = 7 care takers ===> 3 cabs required. ( But the 3rd one have internal fragmentation )

∴ what is the over head = 3 cabs only, right ?

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Yep 

Problem 6.1

 

https://www.google.co.in/url?sa=t&source=web&rct=j&url=http://cnds.eecs.jacobs-university.de/courses/osn-2004/s6.pdf&ved=2ahUKEwiElZ_U-LPeAhVCeH0KHfrZBBIQFjAHegQIBxAB&usg=AOvVaw3w3AcUwvve7wUlV4anKAVn&cshid=1541101946768