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

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Message-ID: <45a44e480710291051s7ffbb582x64ea9524c197b48a@mail.gmail.com>
Date:	Mon, 29 Oct 2007 13:51:46 -0400
From:	"Jaya Kumar" <jayakumar.lkml@...il.com>
To:	"Peter Zijlstra" <peterz@...radead.org>
Cc:	"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 10/29/07, Peter Zijlstra <peterz@...radead.org> wrote:
> On Mon, 2007-10-29 at 01:17 -0700, Jaya Kumar wrote:
> > An aside, I just tested that deferred IO works fine on 2.6.22.10/pxa255.
> >
> > I understood from the thread that PeterZ is looking into page_mkclean
> > changes which I guess went into 2.6.23. I'm also happy to help in any
> > way if the way we're doing fb_defio needs to change.
>
> OK, seems I can't read. Or at least, I missed a large part of the
> problem.
>
> page_mkclean() hasn't changed, it was ->page_mkwrite() that changed. And
> looking at the fb_defio code, I'm not sure I understand how its
> page_mkclean() use could ever have worked.
>
> The proposed patch [1] only fixes the issue of ->page_mkwrite() on
> vmalloc()'ed memory. Not page_mkclean(), and that has never worked from
> what I can make of it.
>
> Jaya, could you shed some light on this? I presume you had your display
> working.
>

I thought I had it working. I saw the display update after each
mmap/write sequence to the framebuffer. I need to check if there's an
munmap or anything else going on in between write sequences that would
cause it to behave like page_mkclean was working.

Is it correct to assume that page_mkclean should mark the pages
read-only so that the next write would again trigger mkwrite? Even if
the page was from a vmalloc_to_page()?

Thanks,
jaya
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