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

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Date:	Tue, 30 Oct 2007 09:16:40 -0400
From:	"Jaya Kumar" <jayakumar.lkml@...il.com>
To:	"Peter Zijlstra" <a.p.zijlstra@...llo.nl>
Cc:	"Andrew Morton" <akpm@...ux-foundation.org>, stefani@...bold.net,
	linux-kernel@...r.kernel.org,
	"David Howells" <dhowells@...hat.com>, linux-mm@...ck.org,
	"Hugh Dickins" <hugh@...itas.com>
Subject: Re: vm_ops.page_mkwrite() fails with vmalloc on 2.6.23

On 10/30/07, Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:
> So page->index does what you want it to, identify which part of the
> framebuffer this particular page belongs to.

Ok. I'm attempting to walk the code sequence. Here's what I think:

- driver loads
- driver vmalloc()s its fb
- this creates the necessary pte entries
then...
- app mmap(/dev/fb0)
- vma is created
- defio mmap adds this vma to private list (equivalent of
address_space or anon_vma)
- app touches base + pixel(128,128) = base + 16k
- page fault
- defio nopage gets called
- defio nopage does vmalloc_to_page(base+16k)
- that finds the correct struct page corresponding to that vaddr.
page->index has not been set by anyone so far, right?
* ah... i see, you are suggesting that this is where I could set the
index since i know the offset i want it to represent. right?
- defio mkwrite get called. defio adds page to its list. schedules delayed work
- app keeps writing the page
- delayed work occurs
- foreach vma { foreach page { page_mkclean_one(page, vma) }
- cycle repeats...

Thanks,
jaya
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