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- Subject: RE: Functions and memory usage
- From: "Alberto Demichelis" <alberto@...>
- Date: Fri, 18 Oct 2002 01:44:57 +0200
> What happens when you deallocate/free an object?
Instead of keeping track of the pages we keep a linked list of feer blocks for every chunk size,
because they are "empty" we use the block himself as node of the linked list so no memory overhead.
When we create a page, the address of the first chunk is aligned in a way that allow us to
retrieve the page start address from the chunk address.The page is ref counted(first 4 bytes).
When we allocate a chunk we pop it from the free list and add a reference to the page.
When we free we put it back in the free list and we decrement the reference if is 0 we free the page.
I've took a quick look at dlmalloc, it looks not so far from our approach exept for the implementation.
I'll test it.
PS: btw 200k/300k are internal structures + "waste".
Crytek Studios GmbH
From: Nick Trout [mailto:email@example.com]
Sent: Freitag, 18. Oktober 2002 01:06
To: Multiple recipients of list
Subject: RE: Functions and memory usage
> 200k/300k of internal structures of the allocator on 100Mb of
> allocated memory sound
> pretty good to me, I do not understand the smile :-)
Then its not memory wasted, its used to manage the memory management. I
assumed you meant that 200k-300k is lost to spaces at the end of pages,
and rounding up, as you describe.
The smile was to show that while I might be aiming a criticism at you
there is no malice intended! Its all a bit dry this technical mumbo
jumbo sometimes and email can often be read ambiguously.
> > I assume each pool size would have an most recently used stack, only
> > allocating a new pool once you've checked the existing
> pools for space?
> I don't really understand the question :P
> What do you mean as most recently used stack?
What happens when you deallocate/free an object? Lets say you allocated
10 pools (4k blocks) of 16 byte objects and then free a load of them. If
you then wanted to allocate a new 16 byte object, how would that be
done? I assume for fast allocation you would keep track of pools, and
group them by size of object, so you could quickly find a pool
containing 16 byte objects to allocate from. I was speculating that a
set of stacks of pools might be a good way to organise this. When a new
pool of a certain size is required it is pushed onto the stack and can
be accessed quickly. However when deallocation takes place this might
not be the best idea. I'd be interested to know how this is managed
since you mention your free time was greatly reduced.
If you are allocating 100Mb then this would be beyond the scope of
certain platforms and so a system like yours may not be as efficient or
suitable for all applications. The dlmalloc system may be a better