Re: [patch 5/6] mm: simplify vmscan vs release refcounting

[Linus Torvalds <torvalds@osdl.org>]

On Thu, 19 Jan 2006, Nick Piggin wrote:
>
> The VM has an interesting race where a page refcount can drop to zero, but
> it is still on the LRU lists for a short time. This was solved by testing
> a 0->1 refcount transition when picking up pages from the LRU, and dropping
> the refcount in that case.

Heh. Now you keep the count offset, but you also end up removing all the 
comments about it (still) being -1 for free. 

And your changelog talks about "atomic_inc_not_zero()" even though the 
code actually does

	atomic_add_unless(&page->_count, 1, -1);

which makes it pretty confusing ;)

I also think it's wrong - you've changed put_page_testzero() to use 
"atomic_dec_and_test()", even though the count is based on -1.

So this patch _only_ works together with the next one, and is invalid in 
many ways on its own. You should re-split the de-skew part correctly..

		Linus
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