linux-kernel - Re: How to get the address of the page structure from the given virtual address?

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Message-ID: <20090811090554.79a1b1ac@bike.lwn.net>
Date:	Tue, 11 Aug 2009 09:05:54 -0600
From:	Jonathan Corbet <corbet@....net>
To:	"B.Vinai Kumar" <vinaibangala2001@...il.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: How to get the address of the page structure from the given
 virtual  address?

On Tue, 11 Aug 2009 20:01:41 +0530
"B.Vinai Kumar" <vinaibangala2001@...il.com> wrote:

> 1) I allocated 8 pages using alloc_pages(GFP_KERNEL, 3). This function
> returns the pointer to the first page's page structure.
> How can I get the page structure address of the remaining 7 pages?

They will be immediately following the first page structure in the
system memory map - they are contiguous pages, after all.  So just use
pointer arithmetic to find them.  

Inquiring minds are indeed curious as to why you need them, though :)
> 
> 2) There is a function page_address() which takes the page structure
> as an argument and returns the virtual address of the page
>  that is pointed by that page structure. 

Note that page_address() may not give you a valid address if it's a
high-memory page which is not currently mapped.

> Is there any method which
> retrives the address of the page structure?

Use virt_to_page() for normal kernel virtual addresses,
vmalloc_to_page() for memory in the vmalloc range.

jon
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