linux-kernel - Re: [PATCH v2 00/12] mm: page migration enhancement for thp

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Date:   Fri, 03 Feb 2017 11:12:12 +0800
From:   "Hillf Danton" <hillf.zj@...baba-inc.com>
To:     "'Zi Yan'" <zi.yan@...rutgers.edu>,
        "'Anshuman Khandual'" <khandual@...ux.vnet.ibm.com>,
        "'Andrew Morton'" <akpm@...ux-foundation.org>,
        "'Naoya Horiguchi'" <n-horiguchi@...jp.nec.com>,
        "'Kirill A. Shutemov'" <kirill.shutemov@...ux.intel.com>
Cc:     <linux-mm@...ck.org>, "'Hugh Dickins'" <hughd@...gle.com>,
        "'Dave Hansen'" <dave.hansen@...el.com>,
        "'Andrea Arcangeli'" <aarcange@...hat.com>,
        "'Mel Gorman'" <mgorman@...hsingularity.net>,
        "'Michal Hocko'" <mhocko@...nel.org>,
        "'Vlastimil Babka'" <vbabka@...e.cz>,
        "'Pavel Emelyanov'" <xemul@...allels.com>,
        "'Balbir Singh'" <bsingharora@...il.com>,
        <linux-kernel@...r.kernel.org>,
        "'Naoya Horiguchi'" <nao.horiguchi@...il.com>
Subject: Re: [PATCH v2 00/12] mm: page migration enhancement for thp


On February 01, 2017 3:54 AM Zi Yan wrote: 
> 
> I am also doing some tests on THP migration and discover that there are
> some corner cases not handled in this patchset.
> 
> For example, in handle_mm_fault, without taking pmd_lock, the kernel may
> see pmd_none(*pmd) during THP migrations, which leads to
> handle_pte_fault or even deeper in the code path. At that moment,
> pmd_trans_unstable() will treat a pmd_migration_entry as pmd_bad and
> clear it. This leads to application crashing and page table leaks, since
> a deposited PTE page is not released when the application crashes.
> 
> Even after I add is_pmd_migration_entry() into pmd_trans_unstable(), I
> still see application data corruptions.
> 
> I hope someone can shed some light on how to debug this. Should I also
> look into pmd_trans_huge() call sites where pmd_migration_entry should
> be handled differently?
> 
Hm ... seems it helps more if you post your current works as RFC on
top of the mm tree, and the relevant tests as well.

Hillf
> 
> Anshuman Khandual wrote:
> > On 11/08/2016 05:01 AM, Naoya Horiguchi wrote:
> >> Hi everyone,
> >>
> >> I've updated thp migration patches for v4.9-rc2-mmotm-2016-10-27-18-27
> >> with feedbacks for ver.1.
> >
> > Hello Noaya,
> >
> > I have been working with Zi Yan on the parallel huge page migration series
> > (https://lkml.org/lkml/2016/11/22/457) and planning to post them on top of
> > this THP migration enhancement series. Hence we were wondering if you have
> > plans to post a new version of this series in near future ?
> >
> > Regards
> > Anshuman
> >
> 
> --
> Best Regards,
> Yan Zi