linux-kernel - Re: [PATCH 2/2] [BUGFIX] pagemap: fix pfn calculation for hugepage

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Date:	Fri, 19 Mar 2010 16:27:32 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	akpm@...ux-foundation.org, andi.kleen@...el.com,
	fengguang.wu@...el.com
Subject: Re: [PATCH 2/2] [BUGFIX] pagemap: fix pfn calculation for hugepage

On Fri, 19 Mar 2010 16:10:23 +0900
KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> wrote:

> On Fri, 19 Mar 2010 15:26:36 +0900
> Naoya Horiguchi <n-horiguchi@...jp.nec.com> wrote:
> 
> > When we look into pagemap using page-types with option -p, the value
> > of pfn for hugepages looks wrong (see below.)
> > This is because pte was evaluated only once for one vma
> > although it should be updated for each hugepage. This patch fixes it.
> > 
> > $ page-types -p 3277 -Nl -b huge
> > voffset   offset  len     flags
> > 7f21e8a00 11e400  1       ___U___________H_G________________
> > 7f21e8a01 11e401  1ff     ________________TG________________
> > 7f21e8c00 11e400  1       ___U___________H_G________________
> > 7f21e8c01 11e401  1ff     ________________TG________________
> >              ^^^
> >              should not be the same
> > 
> > With this patch applied:
> > 
> > $ page-types -p 3386 -Nl -b huge
> > voffset   offset   len    flags
> > 7fec7a600 112c00   1      ___UD__________H_G________________
> > 7fec7a601 112c01   1ff    ________________TG________________
> > 7fec7a800 113200   1      ___UD__________H_G________________
> > 7fec7a801 113201   1ff    ________________TG________________
> >              ^^^
> >              OK
> > 
> Hmm. Is this bug ? To me, it's just shown in hugepage's pagesize, by design.
> 
I'm sorry it seems this is bugfix.

But, this means hugeltb_entry() is not called per hugetlb entry...isn't it ?

Why hugetlb_entry() cannot be called per hugeltb entry ? Don't we need a code
for a case as pmd_size != hugetlb_size in walk_page_range() for generic fix ?

Thanks,
-Kame

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