linux-kernel - Re: [PATCH v2] mm: Fix slab->page

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Message-ID: <alpine.DEB.2.00.1205150903320.6488@router.home>
Date:	Tue, 15 May 2012 09:04:01 -0500 (CDT)
From:	Christoph Lameter <cl@...ux.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
cc:	Pravin B Shelar <pshelar@...ira.com>, penberg@...nel.org,
	mpm@...enic.com, linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	jesse@...ira.com, abhide@...ira.com
Subject: Re: [PATCH v2] mm: Fix slab->page _count corruption.

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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