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

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Date:	Mon, 29 Oct 2007 21:22:26 -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 10/29/07, Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:
>
> [ also, remap_vmalloc_range() suffers similar issues, only file and anon
>   have proper rmap ]
>
> I'm not sure we want full rmap for remap_pfn/vmalloc_range, but perhaps
> we could assist drivers in maintaining and using vma lists.
>
> I think page_mkclean_one() would work if you'd manually set page->index
> and iterate the vmas yourself. Although atm I'm not sure of anything so
> don't pin me on it.

:-) If it's anybody's fault, it's mine for not testing properly. My bad.

In the case of defio, I think it's no trouble to build a list of vmas
at mmap time and then to iterate through them when it's ready for
mkclean time as you suggested. I don't fully understand page->index
yet. I had thought it was only used by swap cache or file map.

On an unrelated note, I was looking for somewhere to stuff a 16 bit
offset (so that I have a cheap way to know which struct page
corresponds to which framebuffer block or offset) for another driver.
I had thought page->index was it but I think I am wrong now.

Thanks,
jaya
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