Re: [PATCH 08/13] mm: remove the mask variable in hmm_vma_walk_hugetlb_entry

From: Jason Gunthorpe <jgg@mellanox.com>
To: Christoph Hellwig <hch@lst.de>
Cc: "Jérôme 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>,
	"dri-devel@lists.freedesktop.org"
	<dri-devel@lists.freedesktop.org>,
	"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
Date: Tue, 30 Jul 2019 17:39:50 +0000	[thread overview]
Message-ID: <20190730173946.GK24038@mellanox.com> (raw)
In-Reply-To: <20190730055203.28467-9-hch@lst.de>

On Tue, Jul 30, 2019 at 08:51:58AM +0300, Christoph Hellwig wrote:
> The pagewalk code already passes the value as the hmask parameter.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
>  mm/hmm.c | 7 ++-----
>  1 file changed, 2 insertions(+), 5 deletions(-)
> 
> 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, unsigned long hmask,
>  				      struct mm_walk *walk)
>  {
>  #ifdef CONFIG_HUGETLB_PAGE
> -	unsigned long addr = start, i, pfn, mask;
> +	unsigned long addr = start, i, pfn;
>  	struct hmm_vma_walk *hmm_vma_walk = walk->private;
>  	struct hmm_range *range = hmm_vma_walk->range;
>  	struct vm_area_struct *vma = walk->vma;
> -	struct hstate *h = hstate_vma(vma);
>  	uint64_t orig_pfn, cpu_flags;
>  	bool fault, write_fault;
>  	spinlock_t *ptl;
>  	pte_t entry;
>  	int ret = 0;
>  
> -	mask = huge_page_size(h) - 1;
> -
>  	ptl = huge_pte_lock(hstate_vma(vma), walk->mm, pte);
>  	entry = huge_ptep_get(pte);
>  
> @@ -799,7 +796,7 @@ static int hmm_vma_walk_hugetlb_entry(pte_t *pte, unsigned long hmask,
>  		goto unlock;
>  	}
>  
> -	pfn = pte_pfn(entry) + ((start & mask) >> PAGE_SHIFT);
> +	pfn = 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 = hstate_vma(vma);
        unsigned long hmask = huge_page_mask(h); // aka h->mask

                        err = 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 = ~((1ULL << (order + PAGE_SHIFT)) - 1);

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

Looks like hmask == ~mask

?

Jason