[Ksummit-discuss] [CORE TOPIC] More useful types in the linux kernel

[David Howells]

Dmitry Torokhov <dmitry.torokhov at gmail.com> wrote:

> >  (1) A 'bits' and maybe a 'bits64' type.  Currently you have to use unsigned
> >      long when you want to deploy a flags field with which you're going to use
> >      test_bit() and co. - but this typically wastes 32 bits on a 64-bit arch
> >      because you can't use bits 32-63 as they might not exist.
> 
> What is wrong with using DECLARE_BITMAP()? It will allocate exactly as
> many unsigned longs

You missed my point.  *unsigned long* is the issue.  The majority of the time
that wastes 32 bits on a 64-bit machine - especially when we don't need that
many flags.  On some 64-bit arches we could use unsigned int instead.

David