Memory allocation usin malloc

Hi Experts,

I am experimenting with how memory is allocated on the heap.  It appears, when I do malloc back to back, the first one returns an address in one page, and the second one returns an address in another page(4096 bytes page size).  I was expecting( most likely incorrectly) that it will be in the same page, but would be separated by the allocation table data.  Does every malloc goes and fetch addresses from different pages?
Thank you.


        int i, j;

	int * firstArray = malloc(sizeof(int)*20);
	int *secondArray = malloc(sizeof(int)*10);
	for( j = 0; j < 5; j++)
	{
		secondArray[j] = 11;
	}
	for( i = 0; i < 25; i++)
	{
		firstArray[i] = 10;
	}

Open in new window

ambuliAsked:
Who is Participating?
I wear a lot of hats...

"The solutions and answers provided on Experts Exchange have been extremely helpful to me over the last few years. I wear a lot of hats - Developer, Database Administrator, Help Desk, etc., so I know a lot of things but not a lot about one thing. Experts Exchange gives me answers from people who do know a lot about one thing, in a easy to use platform." -Todd S.

jkrCommented:
Yup, the 'usual' algorithms for allocating on the heap will either a) rely on undelying OS code or b) offer a scheme where it is most worthwile to fragment the heap as least as possible. So, in your case, the allocator code might have found regions that are better suitable to place your request in other than two consecutive pieces of memory (yet that might happen as well). As a bottom line, assumptions about what heap allocators return are futile at best, better not worry about that in the first place.
0
ambuliAuthor Commented:
sure:-) i was curious as to why it is allocated on a new page. thank you. one more question. I believe the allocation info is usually placed in the block before or after the allocated block. how much of memory is used for this data and what information is stored there. is there any reference doc for this.
0
jkrCommented:
This is completely implementation dependant. I was about to mention that such a 'context record' could have been in the way between you and your contiguous allocations, but if it was me to create a (sub-)allocator, I'd keep that separated from the actual memory pool I was to supervise about. So, I guess my best advice is to make no guesses about what your underlying heap does nor how it is implemented.
0

Experts Exchange Solution brought to you by

Your issues matter to us.

Facing a tech roadblock? Get the help and guidance you need from experienced professionals who care. Ask your question anytime, anywhere, with no hassle.

Start your 7-day free trial
ambuliAuthor Commented:
thanks.  i was studying about heap corruptions and that is why i was interested in.
0
jkrCommented:
As a 'real life' example - I had to design an allocator for a UDF2 file system for real time video recording, and *speed* therefore was the primary  factor - so, find the first slot that satisfies your requirements and move on... (in hindsight, I see much room for optimization ;o)
0
It's more than this solution.Get answers and train to solve all your tech problems - anytime, anywhere.Try it for free Edge Out The Competitionfor your dream job with proven skills and certifications.Get started today Stand Outas the employee with proven skills.Start learning today for free Move Your Career Forwardwith certification training in the latest technologies.Start your trial today
C

From novice to tech pro — start learning today.