[ofa-general] Re: [PATCH 08 of 11] anon-vma-rwsem

[Linus Torvalds]

On Wed, 7 May 2008, Christoph Lameter wrote:
> 
> > (That said, we're not running out of vm flags yet, and if we were, we 
> > could just add another word. We're already wasting that space right now on 
> > 64-bit by calling it "unsigned long").
> 
> We sure have enough flags.

Oh, btw, I was wrong - we wouldn't want to mark the vma's (they are 
unique), we need to mark the address spaces/anonvma's. So the flag would 
need to be in the "struct anon_vma" (and struct address_space), not in the 
vma itself. My bad. So the flag wouldn't be one of the VM_xyzzy flags, and 
would require adding a new field to "struct anon_vma()"

And related to that brain-fart of mine, that obviously also means that 
yes, the locking has to be stronger than "mm->mmap_sem" held for writing, 
so yeah, it would have be a separate global spinlock (or perhaps a 
blocking lock if you have some reason to protect anything else with this 
too).

			Linus