linux-kernel - Re: [PATCH v2 07/12] mm: thp: check pmd migration entry in common path

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Date:   Thu, 10 Nov 2016 17:08:07 +0800
From:   "Hillf Danton" <hillf.zj@...baba-inc.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>,
        "'Anshuman Khandual'" <khandual@...ux.vnet.ibm.com>
Subject: Re: [PATCH v2 07/12] mm: thp: check pmd migration entry in common path

On Tuesday, November 08, 2016 7:32 AM Naoya Horiguchi wrote:
> 
> @@ -1013,6 +1027,9 @@ int do_huge_pmd_wp_page(struct fault_env *fe, pmd_t orig_pmd)
>  	if (unlikely(!pmd_same(*fe->pmd, orig_pmd)))
>  		goto out_unlock;
> 
> +	if (unlikely(!pmd_present(orig_pmd)))
> +		goto out_unlock;
> +

Can we encounter a migration entry after acquiring ptl ?

>  	page = pmd_page(orig_pmd);
>  	VM_BUG_ON_PAGE(!PageCompound(page) || !PageHead(page), page);
>  	/*
[...]
> @@ -3591,6 +3591,10 @@ static int __handle_mm_fault(struct vm_area_struct *vma, unsigned long address,
>  		int ret;
> 
>  		barrier();
> +		if (unlikely(is_pmd_migration_entry(orig_pmd))) {
> +			pmd_migration_entry_wait(mm, fe.pmd);
> +			return 0;
> +		}
>  		if (pmd_trans_huge(orig_pmd) || pmd_devmap(orig_pmd)) {
>  			if (pmd_protnone(orig_pmd) && vma_is_accessible(vma))
>  				return do_huge_pmd_numa_page(&fe, orig_pmd);