Re: Linux 2.6.20-rc7

[Nick Piggin]

Linus Torvalds wrote:

> 	if (free_pages <= min + z->lowmem_reserve[classzone_idx])
> 		return 0;
>
> gets broken, because the negative 'free_pages' will look like a huge 
> unsigned positive number (and we'll make it unsigned becaue 'min' got 
> turned unsigned). There was a reason that thing was signed in the first 
> place, and neither me nor Andrew noticed.
>
> Bad Nick. And bad me and Andrew for not noticing.

Sorry. I think I even wrote that comment at the top of the function.
And probably the function as well :(

> I should either revert that commit or just check for "free_pages" being 
> negative. The latter, in many ways, is probably better, because generally 
> we simply should never work with negative numbers in the kernel, so when 
> something potentially goes negative, we're probably just better off always 
> testing it explicitly anyway.
>
> Nick, Andrew, any preferences? 

As Andrew says, it would need to be checked each time, because we have
nothing synchronising against free_pages at the top, or nr_free in the
loop.

We could make them both unsigned, and _add_ everything to min rather than
subtracting from free_pages?

--
SUSE Labs, Novell Inc.
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