Re: Linux 2.6.20-rc7

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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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