linux-kernel - Re: [PATCH 1/2] mm,thp: refactor generic deposit/withdraw routines for wider usage

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Date:	Thu, 11 Feb 2016 11:22:23 +0100
From:	Martin Schwidefsky <schwidefsky@...ibm.com>
To:	Vineet Gupta <Vineet.Gupta1@...opsys.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	"David S. Miller" <davem@...emloft.net>,
	Alex Thorlton <athorlton@....com>,
	Gerald Schaefer <gerald.schaefer@...ibm.com>,
	<linux-snps-arc@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
	<linux-arch@...r.kernel.org>,
	Andrea Arcangeli <aarcange@...hat.com>
Subject: Re: [PATCH 1/2] mm,thp: refactor generic deposit/withdraw routines
 for wider usage

On Thu, 11 Feb 2016 14:58:26 +0530
Vineet Gupta <Vineet.Gupta1@...opsys.com> wrote:

> Generic pgtable_trans_huge_deposit()/pgtable_trans_huge_withdraw()
> assume pgtable_t to be struct page * which is not true for all arches.
> Thus arc, s390, sparch end up with their own copies despite no special
> hardware requirements (unlike powerpc).

s390 does have a special hardware requirement. pgtable_t is an address
for a 2K block of memory. It is *not* equivalent to a struct page *
which refers to a 4K block of memory. That has been the whole point
to introduce pgtable_t.

> It seems massaging the code a bit can make it reusbale.

Imho the new code for asm-generic looks fine, as long as the override
with __HAVE_ARCH_PGTABLE_DEPOSIT/__HAVE_ARCH_PGTABLE_WITHDRAW continues
to work I do not mind.

-- 
blue skies,
   Martin.

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