std::string::reserve()

[Paolo Carlini]

Neil Ferguson wrote:

> Shrink-to-fit became significant for me when I discovered that users 
> of libstdc++ here at ESO were reading large blocks of data from files 
> into strings, without knowing how big the blocks were until reaching 
> the end of said blocks.

Humm, what about exact-shrink-to-fit *always*? I mean, not attempting at 
all to round to pagesize when the user code calls reserve(< capacity)? 
If, in your experience, this looks fine, we can implement it easily, 
changing only _S_create in a very clean way. And of course your original 
concern would "magically" ;) disappear... In my opinion, the idea makes 
sense, since, in those specific situations when the user really asks for 
shrink-to-fit, doing our best to achieve it is more important than 
rounding to pagesize and trying to be smart wrt malloc requests.

Just le me know: I can quickly prepare a patch and your users can test 
it for a while.

Paolo.