linux-kernel - Re: [PATCH v2 05/12] mm: thp: add core routines for thp/pmd migration

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Date:   Thu, 10 Nov 2016 13:59:03 +0530
From:   Anshuman Khandual <khandual@...ux.vnet.ibm.com>
To:     Naoya Horiguchi <n-horiguchi@...jp.nec.com>, linux-mm@...ck.org
Cc:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Hugh Dickins <hughd@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        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>,
        Zi Yan <zi.yan@...rutgers.edu>,
        Balbir Singh <bsingharora@...il.com>,
        linux-kernel@...r.kernel.org,
        Naoya Horiguchi <nao.horiguchi@...il.com>
Subject: Re: [PATCH v2 05/12] mm: thp: add core routines for thp/pmd migration

On 11/08/2016 05:01 AM, Naoya Horiguchi wrote:
> This patch prepares thp migration's core code. These code will be open when
> unmap_and_move() stops unconditionally splitting thp and get_new_page() starts
> to allocate destination thps.
> 

Snip

> Signed-off-by: Naoya Horiguchi <n-horiguchi@...jp.nec.com>
> ---
> ChangeLog v1 -> v2:
> - support pte-mapped thp, doubly-mapped thp
> ---
>  arch/x86/include/asm/pgtable_64.h |   2 +
>  include/linux/swapops.h           |  61 +++++++++++++++
>  mm/huge_memory.c                  | 154 ++++++++++++++++++++++++++++++++++++++
>  mm/migrate.c                      |  44 ++++++++++-
>  mm/pgtable-generic.c              |   3 +-
>  5 files changed, 262 insertions(+), 2 deletions(-)


> diff --git v4.9-rc2-mmotm-2016-10-27-18-27/mm/pgtable-generic.c v4.9-rc2-mmotm-2016-10-27-18-27_patched/mm/pgtable-generic.c
> index 71c5f91..6012343 100644
> --- v4.9-rc2-mmotm-2016-10-27-18-27/mm/pgtable-generic.c
> +++ v4.9-rc2-mmotm-2016-10-27-18-27_patched/mm/pgtable-generic.c
> @@ -118,7 +118,8 @@ pmd_t pmdp_huge_clear_flush(struct vm_area_struct *vma, unsigned long address,
>  {
>  	pmd_t pmd;
>  	VM_BUG_ON(address & ~HPAGE_PMD_MASK);
> -	VM_BUG_ON(!pmd_trans_huge(*pmdp) && !pmd_devmap(*pmdp));
> +	VM_BUG_ON(pmd_present(*pmdp) && !pmd_trans_huge(*pmdp) &&
> +		  !pmd_devmap(*pmdp))

Its a valid VM_BUG_ON check but is it related to THP migration or
just a regular fix up ?