From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Subject: Re: [PATCHv5 22/36] mm, hugetlb: switch hugetlbfs to multi-order
 radix-tree entries
Date: Wed, 30 Nov 2016 16:15:34 +0300
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Cc: 'Theodore Ts'o' <tytso@mit.edu>,
        'Andreas Dilger' <adilger.kernel@dilger.ca>,
        'Jan Kara' <jack@suse.com>,
        'Andrew Morton' <akpm@linux-foundation.org>,
        'Alexander Viro' <viro@zeniv.linux.org.uk>,
        'Hugh Dickins' <hughd@google.com>,
        'Andrea Arcangeli' <aarcange@redhat.com>,
        'Dave Hansen' <dave.hansen@intel.com>,
        'Vlastimil Babka' <vbabka@suse.cz>,
        'Matthew Wilcox' <willy@infradead.org>,
        'Ross Zwisler' <ross.zwisler@linux.intel.com>,
        linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        linux-block@vger.kernel.org,
        'Naoya Horiguchi' <n-horiguchi@ah.jp.nec.com>
To: Hillf Danton <hillf.zj@alibaba-inc.com>
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On Wed, Nov 30, 2016 at 05:48:05PM +0800, Hillf Danton wrote:
> On Tuesday, November 29, 2016 7:23 PM Kirill A. Shutemov wrote:
> > @@ -607,10 +605,10 @@ static long hugetlbfs_fallocate(struct file *file, int mode, loff_t offset,
> >  		}
> > 
> >  		/* Set numa allocation policy based on index */
> > -		hugetlb_set_vma_policy(&pseudo_vma, inode, index);
> > +		hugetlb_set_vma_policy(&pseudo_vma, inode, index >> huge_page_order(h));
> > 
> >  		/* addr is the offset within the file (zero based) */
> > -		addr = index * hpage_size;
> > +		addr = index << PAGE_SHIFT & ~huge_page_mask(h);
> > 
> >  		/* mutex taken here, fault path and hole punch */
> >  		hash = hugetlb_fault_mutex_hash(h, mm, &pseudo_vma, mapping,
> 
> Seems we can't use index in computing hash as long as it isn't in huge page size.

Look at changes in hugetlb_fault_mutex_hash(): we shift the index right by
huge_page_order(), before calculating the hash. I don't see a problem
here.

-- 
 Kirill A. Shutemov