Subject: Re: vm_ops.page_mkwrite() fails with vmalloc on 2.6.23
From: Peter Zijlstra <peterz@infradead.org>
To: Jaya Kumar <jayakumar.lkml@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>, stefani@seibold.net,
       linux-kernel@vger.kernel.org, David Howells <dhowells@redhat.com>,
       linux-mm@kvack.org
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	 <45a44e480710291051s7ffbb582x64ea9524c197b48a@mail.gmail.com>
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Date: Mon, 29 Oct 2007 19:17:19 +0100
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On Mon, 2007-10-29 at 13:51 -0400, Jaya Kumar wrote:
> On 10/29/07, Peter Zijlstra <peterz@infradead.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?

Well, yes, that is the intended behaviour.

>  Even if the page was from a vmalloc_to_page()?

That is the crux, I only ever implemented it for file pages.


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