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From: "Zi Yan" <zi.yan@cs.rutgers.edu>
Subject: Re: [PATCH] mm: hugepage: mark splitted page dirty when needed
Date: Tue, 04 Sep 2018 10:00:28 -0400
Message-ID: <D3B32B41-61D5-47B3-B1FC-77B0F71ADA47@cs.rutgers.edu>
In-Reply-To: <20180904080115.o2zj4mlo7yzjdqfl@kshutemo-mobl1>
References: <20180904075510.22338-1-peterx@redhat.com>
 <20180904080115.o2zj4mlo7yzjdqfl@kshutemo-mobl1>
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To: "Kirill A. Shutemov" <kirill@shutemov.name>, Peter Xu <peterx@redhat.com>
Cc: linux-kernel@vger.kernel.org, Andrea Arcangeli <aarcange@redhat.com>, Andrew Morton <akpm@linux-foundation.org>, "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>, Michal Hocko <mhocko@suse.com>, Huang Ying <ying.huang@intel.com>, Dan Williams <dan.j.williams@intel.com>, Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>, =?utf-8?b?SsOpcsO0bWU=?= Glisse <jglisse@redhat.com>, "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>, Konstantin Khlebnikov <khlebnikov@yandex-team.ru>, Souptick Joarder <jrdr.linux@gmail.com>, linux-mm@kvack.org

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On 4 Sep 2018, at 4:01, Kirill A. Shutemov wrote:

> On Tue, Sep 04, 2018 at 03:55:10PM +0800, Peter Xu wrote:
>> When splitting a huge page, we should set all small pages as dirty if
>> the original huge page has the dirty bit set before.  Otherwise we'll
>> lose the original dirty bit.
>
> We don't lose it. It got transfered to struct page flag:
>
> 	if (pmd_dirty(old_pmd))
> 		SetPageDirty(page);
>

Plus, when split_huge_page_to_list() splits a THP, its subroutine __split_huge_page()
propagates the dirty bit in the head page flag to all subpages in __split_huge_page_tail().

--
Best Regards
Yan Zi

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