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From Sander Striker <stri...@apache.org>
Subject Re: Dangerous Flood memory model compromises larger runs
Date Fri, 14 Nov 2003 00:35:27 GMT
On Thu, 2003-11-13 at 16:26, Cliff Woolley wrote:
> On Thu, 13 Nov 2003, Norman Tuttle wrote:
> 
> > How do the pools define "if possible" in your wording below (i.e., how
> > would the pool know when to reuse memory)?
> 
> It's kind of complicated, so I don't know how well I can explain it off
> the top of my head (Sander, feel free to jump in here :), but it keeps
> freelist buckets of varying power-of-two sizes, and if it finds one of the
> appropriate size, it will use it.

The allocator keeps freelists of multiples of 4k blocks actually ;)

> But there are two levels of things going on, too, because the allocator
> hands out blocks of a certain size, which the pools then divide up into
> smaller blocks...

Pools get blocks from the allocator.  Pools then hand out the requested
memory to the caller.  They hold on to the 'surplus' for the next
allocation.

On a pool clear, all used blocks return to the allocator (except for
the block containing the pool itself (8k)).

> Oy.
> 
> Sander?  Help me out.  :)

You know what, this question comes up reasonably frequently.  Enough for
me to start writing a document on this.

I'll post a URL later on.


Sander

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