linux-kernel - Re: [PATCH] mm: hugepage: mark splitted page dirty when needed

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Message-ID: <D3B32B41-61D5-47B3-B1FC-77B0F71ADA47@cs.rutgers.edu>
Date:   Tue, 04 Sep 2018 10:00:28 -0400
From:   "Zi Yan" <zi.yan@...rutgers.edu>
To:     "Kirill A. Shutemov" <kirill@...temov.name>,
        "Peter Xu" <peterx@...hat.com>
Cc:     linux-kernel@...r.kernel.org,
        "Andrea Arcangeli" <aarcange@...hat.com>,
        "Andrew Morton" <akpm@...ux-foundation.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        "Michal Hocko" <mhocko@...e.com>,
        "Huang Ying" <ying.huang@...el.com>,
        "Dan Williams" <dan.j.williams@...el.com>,
        "Naoya Horiguchi" <n-horiguchi@...jp.nec.com>,
        "Jérôme Glisse" <jglisse@...hat.com>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
        "Konstantin Khlebnikov" <khlebnikov@...dex-team.ru>,
        "Souptick Joarder" <jrdr.linux@...il.com>, linux-mm@...ck.org
Subject: Re: [PATCH] mm: hugepage: mark splitted page dirty when needed

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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