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Date:   Thu, 12 Jan 2023 13:02:17 -0500
From:   Peter Xu <peterx@redhat.com>
To:     James Houghton <jthoughton@google.com>
Cc:     Mike Kravetz <mike.kravetz@oracle.com>,
        Muchun Song <songmuchun@bytedance.com>,
        David Hildenbrand <david@redhat.com>,
        David Rientjes <rientjes@google.com>,
        Axel Rasmussen <axelrasmussen@google.com>,
        Mina Almasry <almasrymina@google.com>,
        Zach O'Keefe <zokeefe@google.com>,
        Manish Mishra <manish.mishra@nutanix.com>,
        Naoya Horiguchi <naoya.horiguchi@nec.com>,
        "Dr . David Alan Gilbert" <dgilbert@redhat.com>,
        "Matthew Wilcox (Oracle)" <willy@infradead.org>,
        Vlastimil Babka <vbabka@suse.cz>,
        Baolin Wang <baolin.wang@linux.alibaba.com>,
        Miaohe Lin <linmiaohe@huawei.com>,
        Yang Shi <shy828301@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 19/46] hugetlb: add HGM support for follow_hugetlb_page
Message-ID: <Y8BLKaKy9CUCy/vy@x1n>
References: <20230105101844.1893104-1-jthoughton@google.com>
 <20230105101844.1893104-20-jthoughton@google.com>
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On Thu, Jan 05, 2023 at 10:18:17AM +0000, James Houghton wrote:
> @@ -6731,22 +6746,22 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
>  		 * and skip the same_page loop below.
>  		 */
>  		if (!pages && !vmas && !pfn_offset &&
> -		    (vaddr + huge_page_size(h) < vma->vm_end) &&
> -		    (remainder >= pages_per_huge_page(h))) {
> -			vaddr += huge_page_size(h);
> -			remainder -= pages_per_huge_page(h);
> -			i += pages_per_huge_page(h);
> +		    (vaddr + pages_per_hpte < vma->vm_end) &&
> +		    (remainder >= pages_per_hpte)) {
> +			vaddr += pages_per_hpte;

This silently breaks hugetlb GUP.. should be

                        vaddr += hugetlb_pte_size(&hpte);

It caused misterious MISSING events when I'm playing with this tree, and
I'm surprised it rooted here.  So far the most time consuming one. :)

> +			remainder -= pages_per_hpte;
> +			i += pages_per_hpte;
>  			spin_unlock(ptl);
>  			hugetlb_vma_unlock_read(vma);
>  			continue;
>  		}

-- 
Peter Xu