Re: [boost] [review] The review of Boost.DoubleEnded starts today: September 21 - September 30

Subject: Re: [boost] [review] The review of Boost.DoubleEnded starts today: September 21 - September 30
From: Thorsten Ottosen (tottosen_at_[hidden])
Date: 2017-09-29 07:30:01

Den 28-09-2017 kl. 21:35 skrev Ion Gaztañaga via Boost:
> On 28/09/2017 10:49, Thorsten Ottosen via Boost wrote:
>> Reading through the argument, there are a few things I don't get.
>> Is seems that the proof sort of assumes one container instance. And 
>> will the heap manager actually coalesce anything?
> 
> DLMalloc coalesces. Several heap managers coalesce when the allocation 
> is bigger than a limit. Boost.Interprocess allocators coalesce.
> 
> I'm not sure what jemalloc and similar allocators do.

Yes, there seem to be many takes on this. Stuff like

http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2013/n3536.html

seem to suggest that a larger chunk is independent of smaller chunks.

The argument says we are looking for

   \sum_{j=o}^{i-1} S[j] >= S[i+1]

so the coalescing is supposed to happen between the i'th and (i+1)'th 
allocation.

Now, if there are two vectors in play, or other data structures that 
uses memory, surely those leftovers can be coalesced into something
that satisfy a larger growth factor.

kind regards

-Thorsten