linux-kernel - Re: Re: [PATCH] futex: bugfix for futex-key conflict when futex use hugepage

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Message-ID: <OF137D0ABE.5A739596-ON48257B50.002AB95E-48257B50.002AD807@zte.com.cn>
Date:	Wed, 17 Apr 2013 15:47:23 +0800
From:	zhang.yi20@....com.cn
To:	Dave Hansen <dave.hansen@...ux.intel.com>
Cc:	Darren Hart <dvhart@...ux.intel.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: Re: [PATCH] futex: bugfix for futex-key conflict when futex use
 hugepage

Dave Hansen <dave.hansen@...ux.intel.com> wrote on 2013/04/17 02:37:40:

> Instead of bothering to store the index, why not just calculate it, 
like:
> 
> On 04/15/2013 08:37 PM, zhang.yi20@....com.cn wrote:
> > +static inline int get_page_compound_index(struct page *page)
> > +{
> > +       if (PageHead(page))
> > +               return 0;
> > +       return compound_head(page) - page;
> > +}
> 
> BTW, you've really got to get your mail client fixed.  Your patch is
> still line-wrapped.


I agree that I should calculate the compound index, but refer to 
prep_compound_gigantic_page, I think it may like this:

+static inline int get_page_compound_index(struct page *page)
+{
+       struct page *head_page;
+       if (PageHead(page))
+               return 0;
+
+       head_page = compound_head(page);
+       if (compound_order(head_page) >= MAX_ORDER)
+               return page_to_pfn(page) - page_to_pfn(head_page);
+       else
+               return page - compound_head(page);
+}
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