linux-kernel - Re: [PATCH v3 1/2] mm: migration: fix migration of huge PMD shared pages

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Message-ID: <20180823124855.GI29735@dhcp22.suse.cz>
Date:   Thu, 23 Aug 2018 14:48:55 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Mike Kravetz <mike.kravetz@...cle.com>
Cc:     kbuild test robot <lkp@...el.com>, kbuild-all@...org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Jérôme Glisse <jglisse@...hat.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
        Davidlohr Bueso <dave@...olabs.net>,
        Andrew Morton <akpm@...ux-foundation.org>,
        stable@...r.kernel.org
Subject: Re: [PATCH v3 1/2] mm: migration: fix migration of huge PMD shared
 pages

On Tue 21-08-18 18:10:42, Mike Kravetz wrote:
[...]

OK, after burning myself when trying to be clever here it seems like
your proposed solution is indeed simpler.

> +bool huge_pmd_sharing_possible(struct vm_area_struct *vma,
> +				unsigned long *start, unsigned long *end)
> +{
> +	unsigned long check_addr = *start;
> +	bool ret = false;
> +
> +	if (!(vma->vm_flags & VM_MAYSHARE))
> +		return ret;
> +
> +	for (check_addr = *start; check_addr < *end; check_addr += PUD_SIZE) {
> +		unsigned long a_start = check_addr & PUD_MASK;
> +		unsigned long a_end = a_start + PUD_SIZE;

I guess this should be rather in HPAGE_SIZE * PTRS_PER_PTE units as
huge_pmd_unshare does.
-- 
Michal Hocko
SUSE Labs