linux-kernel - Re: oops in copy_page

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Message-ID: <20130108180302.GA27871@shutemov.name>
Date:	Tue, 8 Jan 2013 20:03:02 +0200
From:	"Kirill A. Shutemov" <kirill@...temov.name>
To:	Andrea Arcangeli <aarcange@...hat.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Hillf Danton <dhillf@...il.com>,
	Hugh Dickins <hughd@...gle.com>, Dave Jones <davej@...hat.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>, Linux-MM <linux-mm@...ck.org>,
	Rik van Riel <riel@...hat.com>
Subject: Re: oops in copy_page_rep()

On Tue, Jan 08, 2013 at 06:49:51PM +0100, Andrea Arcangeli wrote:
> Hi Kirill,
> 
> On Tue, Jan 08, 2013 at 07:30:58PM +0200, Kirill A. Shutemov wrote:
> > Merged patch is obviously broken: huge_pmd_set_accessed() can be called
> > only if the pmd is under splitting.
> 
> Of course I assume you meant "only if the pmd is not under splitting".

The broken merged patch has this:

+                       if (dirty && !pmd_write(orig_pmd) &&
                            !pmd_trans_splitting(orig_pmd)) {
			[...]
+                       } else {
+                               huge_pmd_set_accessed(mm, vma, address, pmd,
+                                                     orig_pmd, dirty);
                        }

> But no, setting a bitflag like the young bit or clearing or setting
> the numa bit won't screw with split_huge_page and it's safe even if
> the pmd is under splitting.

Okay. Thanks for clarification for me.

-- 
 Kirill A. Shutemov
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