linux-kernel - Re: [PATCH v12 5/6] khugepaged: enable collapse pmd for pte-mapped THP

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Date:   Mon, 12 Aug 2019 15:22:58 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     "Kirill A. Shutemov" <kirill@...temov.name>
Cc:     Song Liu <songliubraving@...com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux MM <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Matthew Wilcox <matthew.wilcox@...cle.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Kernel Team <Kernel-team@...com>,
        William Kucharski <william.kucharski@...cle.com>,
        "srikar@...ux.vnet.ibm.com" <srikar@...ux.vnet.ibm.com>
Subject: Re: [PATCH v12 5/6] khugepaged: enable collapse pmd for pte-mapped
 THP

On 08/12, Kirill A. Shutemov wrote:
>
> On Fri, Aug 09, 2019 at 06:01:18PM +0000, Song Liu wrote:
> > +		if (pte_none(*pte) || !pte_present(*pte))
> > +			continue;
>
> You don't need to check both. Present is never none.

Agreed.

Kirill, while you are here, shouldn't retract_page_tables() check
vma->anon_vma (and probably do mm_find_pmd) under vm_mm->mmap_sem?

Can't it race with, say, do_cow_fault?

Oleg.