linux-kernel - Re: [PATCHv5 22/36] mm, hugetlb: switch hugetlbfs to multi-order radix-tree entries

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Date:   Thu, 01 Dec 2016 11:10:52 +0800
From:   "Hillf Danton" <hillf.zj@...baba-inc.com>
To:     "'Kirill A. Shutemov'" <kirill.shutemov@...ux.intel.com>
Cc:     "'Theodore Ts'o'" <tytso@....edu>,
        "'Andreas Dilger'" <adilger.kernel@...ger.ca>,
        "'Jan Kara'" <jack@...e.com>,
        "'Andrew Morton'" <akpm@...ux-foundation.org>,
        "'Alexander Viro'" <viro@...iv.linux.org.uk>,
        "'Hugh Dickins'" <hughd@...gle.com>,
        "'Andrea Arcangeli'" <aarcange@...hat.com>,
        "'Dave Hansen'" <dave.hansen@...el.com>,
        "'Vlastimil Babka'" <vbabka@...e.cz>,
        "'Matthew Wilcox'" <willy@...radead.org>,
        "'Ross Zwisler'" <ross.zwisler@...ux.intel.com>,
        <linux-ext4@...r.kernel.org>, <linux-fsdevel@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
        <linux-block@...r.kernel.org>,
        "'Naoya Horiguchi'" <n-horiguchi@...jp.nec.com>
Subject: Re: [PATCHv5 22/36] mm, hugetlb: switch hugetlbfs to multi-order radix-tree entries

On Wednesday, November 30, 2016 9:16 PM Kirill A. Shutemov wrote:
> 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.
> 
You are right. I missed that critical point.

thanks
Hillf