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

[Linus Torvalds]

On Thu, 8 May 2008, Andrea Arcangeli wrote:
> 
> So because the bitflag can't prevent taking the same lock twice on two
> different vmas in the same mm, we still can't remove the sorting

Andrea. 

Take five minutes. Take a deep breadth. And *think* about actually reading 
what I wrote.

The bitflag *can* prevent taking the same lock twice. It just needs to be 
in the right place.

Let me quote it for you:

> So the flag wouldn't be one of the VM_xyzzy flags, and would require 
> adding a new field to "struct anon_vma()"

IOW, just make it be in that anon_vma (and the address_space). No sorting 
required.

> I think it's more interesting to put a cap on the number of vmas to
> min(1024,max_map_count). The sort time on an 8k array runs in constant
> time.

Shut up already. It's not constant time just because you can cap the 
overhead. We're not in a university, and we care about performance, not 
your made-up big-O notation.

			Linus