linux-kernel - Re: [RFC v2 PATCH 1/7] thp: remove assumptions on pgtable

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Message-ID: <20120831091012.7b710326@de.ibm.com>
Date:	Fri, 31 Aug 2012 09:10:12 +0200
From:	Martin Schwidefsky <schwidefsky@...ibm.com>
To:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
Cc:	Gerald Schaefer <gerald.schaefer@...ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Andi Kleen <ak@...ux.intel.com>,
	Hugh Dickins <hughd@...gle.com>,
	Hillf Danton <dhillf@...il.com>, linux-kernel@...r.kernel.org,
	Heiko Carstens <heiko.carstens@...ibm.com>
Subject: Re: [RFC v2 PATCH 1/7] thp: remove assumptions on pgtable_t type

On Fri, 31 Aug 2012 10:59:38 +0530
"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com> wrote:

> Gerald Schaefer <gerald.schaefer@...ibm.com> writes:
> 
> > The thp page table pre-allocation code currently assumes that pgtable_t
> > is of type "struct page *". This may not be true for all architectures,
> > so this patch removes that assumption by replacing the functions
> > prepare_pmd_huge_pte() and get_pmd_huge_pte() with two new functions
> > that can be defined architecture-specific.
> >
> > It also removes two VM_BUG_ON checks for page_count() and page_mapcount()
> > operating on a pgtable_t. Apart from the VM_BUG_ON removal, there will
> > be no functional change introduced by this patch.
> 
> Why is that VM_BUG_ON not needed any more ? What is that changed which break
> that requirement ?

Because pgtable_t for s390 is not a page and there simply is no page_count or
page_mapcount.

-- 
blue skies,
   Martin.

"Reality continues to ruin my life." - Calvin.

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