linux-kernel - Re: vm_ops.page_mkwrite() fails with vmalloc on 2.6.23

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Date:	Tue, 30 Oct 2007 16:51:02 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Hugh Dickins <hugh@...itas.com>
Cc:	Jaya Kumar <jayakumar.lkml@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>, stefani@...bold.net,
	linux-kernel@...r.kernel.org, David Howells <dhowells@...hat.com>,
	linux-mm@...ck.org
Subject: Re: vm_ops.page_mkwrite() fails with vmalloc on 2.6.23

On Tue, 2007-10-30 at 15:47 +0000, Hugh Dickins wrote:
> On Tue, 30 Oct 2007, Peter Zijlstra wrote:
> > On Tue, 2007-10-30 at 09:16 -0400, Jaya Kumar wrote:
> ....
> > > - defio mmap adds this vma to private list (equivalent of
> > > address_space or anon_vma)
> ....
> > > - foreach vma { foreach page { page_mkclean_one(page, vma) }
> > 
> > Yeah, page_mkclean_one(page, vma) will use vma_address() to obtain an
> > user-space address for the page in this vma using page->index and the
> > formula from the last email, this address is then used to walk the page
> > tables and obtain a pte.
> 
> I don't understand why you suggested an anon_vma, nor why Jaya is
> suggesting a private list.  All vmas mapping /dev/fb0 will be kept
> in the prio_tree rooted in its struct address_space (__vma_link_file
> in mm/mmap.c).  And page_mkclean gets page_mkclean_file to walk that
> very tree.  The missing part is just the setting of page->mapping to
> point to that struct address_space (and clearing it before finally
> freeing the pages), and the setting of page->index as you described.
> Isn't it?

Hmm, there is a thought. I had not considered that mapping a chardev
would have that effect.

I'd have to have a look at the actual code, but yeah, that might very
well work out. How silly of me.

Thanks!

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