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From:   Jason Gunthorpe <jgg@mellanox.com>
To:     Christoph Hellwig <hch@lst.de>
CC:     =?iso-8859-1?Q?J=E9r=F4me_Glisse?= <jglisse@redhat.com>,
        Ben Skeggs <bskeggs@redhat.com>,
        Felix Kuehling <Felix.Kuehling@amd.com>,
        Ralph Campbell <rcampbell@nvidia.com>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
        "nouveau@lists.freedesktop.org" <nouveau@lists.freedesktop.org>,
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        "amd-gfx@lists.freedesktop.org" <amd-gfx@lists.freedesktop.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 08/13] mm: remove the mask variable in
 hmm_vma_walk_hugetlb_entry
Thread-Topic: [PATCH 08/13] mm: remove the mask variable in
 hmm_vma_walk_hugetlb_entry
Thread-Index: AQHVRpsBxp87/2vfUUuxY9sZD/Qj2KbjblgA
Date:   Tue, 30 Jul 2019 17:39:50 +0000
Message-ID: <20190730173946.GK24038@mellanox.com>
References: <20190730055203.28467-1-hch@lst.de>
 <20190730055203.28467-9-hch@lst.de>
In-Reply-To: <20190730055203.28467-9-hch@lst.de>
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On Tue, Jul 30, 2019 at 08:51:58AM +0300, Christoph Hellwig wrote:
> The pagewalk code already passes the value as the hmask parameter.
>=20
> Signed-off-by: Christoph Hellwig <hch@lst.de>
>  mm/hmm.c | 7 ++-----
>  1 file changed, 2 insertions(+), 5 deletions(-)
>=20
> diff --git a/mm/hmm.c b/mm/hmm.c
> index f26d6abc4ed2..88b77a4a6a1e 100644
> +++ b/mm/hmm.c
> @@ -771,19 +771,16 @@ static int hmm_vma_walk_hugetlb_entry(pte_t *pte, u=
nsigned long hmask,
>  				      struct mm_walk *walk)
>  {
>  #ifdef CONFIG_HUGETLB_PAGE
> -	unsigned long addr =3D start, i, pfn, mask;
> +	unsigned long addr =3D start, i, pfn;
>  	struct hmm_vma_walk *hmm_vma_walk =3D walk->private;
>  	struct hmm_range *range =3D hmm_vma_walk->range;
>  	struct vm_area_struct *vma =3D walk->vma;
> -	struct hstate *h =3D hstate_vma(vma);
>  	uint64_t orig_pfn, cpu_flags;
>  	bool fault, write_fault;
>  	spinlock_t *ptl;
>  	pte_t entry;
>  	int ret =3D 0;
> =20
> -	mask =3D huge_page_size(h) - 1;
> -
>  	ptl =3D huge_pte_lock(hstate_vma(vma), walk->mm, pte);
>  	entry =3D huge_ptep_get(pte);
> =20
> @@ -799,7 +796,7 @@ static int hmm_vma_walk_hugetlb_entry(pte_t *pte, uns=
igned long hmask,
>  		goto unlock;
>  	}
> =20
> -	pfn =3D pte_pfn(entry) + ((start & mask) >> PAGE_SHIFT);
> +	pfn =3D pte_pfn(entry) + ((start & hmask) >> PAGE_SHIFT);

I don't know this hstate stuff, but this doesn't look the same?

static int walk_hugetlb_range(unsigned long addr, unsigned long end, {
        struct hstate *h =3D hstate_vma(vma);
        unsigned long hmask =3D huge_page_mask(h); // aka h->mask

                        err =3D walk->hugetlb_entry(pte, hmask, addr, next,=
 walk);

And the first place I found setting h->mask is:

void __init hugetlb_add_hstate(unsigned int order) {
	h->mask =3D ~((1ULL << (order + PAGE_SHIFT)) - 1);

Compared with
    mask =3D huge_page_size(h) - 1;
         =3D ((unsigned long)PAGE_SIZE << h->order) - 1

Looks like hmask =3D=3D ~mask

?

Jason