re: pg->offset and pg->flags

[matthew green <mrg%eterna.com.au@localhost>]

> On Sun, Apr 03, 2011 at 07:35:04PM +1000, matthew green wrote:
> > 
> > > Ignoring the free page allocator which abuses pg->offset, is there any
> > > reason we cannot fold pg->flags into pg->offset?  The lower PAGE_SHIFT 
> > > bits
> > > of pg->offset are not used.
> > 
> > is this about making vm_page smaller?  if so, and it works, i guess that
> > seems fine, but how many bits do you want to use?  ie, what is the
> > smallest PAGE_SIZE we will support?
> > 
> > if not that, why?
> 
> And is the memory saved enough to be significant compared to the
> number of masking operations needed to get pg->offset.

actually, it won't really help unless we rearrange a lot more in
vm_page{}.  right now the flags member is 1 uint16_t in a series
of 4 in a row, so removing one is unlikely to help, as it will
just introduce padding on most platforms.


.mrg.