Date: Tue, 15 May 2012 09:04:01 -0500 (CDT)
From: Christoph Lameter <cl@linux.com>
To: Eric Dumazet <eric.dumazet@gmail.com>
cc: Pravin B Shelar <pshelar@nicira.com>, penberg@kernel.org, mpm@selenic.com,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org, jesse@nicira.com,
        abhide@nicira.com
Subject: Re: [PATCH v2] mm: Fix slab->page _count corruption.
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On Tue, 15 May 2012, Eric Dumazet wrote:

> > Following patch fixes it by moving page->_count out of cmpxchg_double
> > data. So that slub does no change it while updating slub meta-data in
> > struct page.
>
> I say again : Page is owned by slub, so get_page() or put_page() is not
> allowed ?

It is allowed since slab memory can be used for DMA.

> How is put_page() going to work with order-1 or order-2 allocations ?

It is always incrementing the page count of the head page.
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