mmap question

[Eric Van Hensbergen <ericvh@gmail.com>]

On Mon, 21 Mar 2005 13:33:55 -0800, Bryan Henderson <hbryan@us.ibm.com> wrote:
> >I want all my file system's operations to be complete uncached and
> >synchronous, but I also want to support mmap.
> >...
> >What am I doing wrong?  Is what I'm trying to do impossible, and if
> >so, how can I get as close as possible?
>
> It looks to me like you're running into the fundamental limitation that
> the CPU doesn't notify Linux every time you store into a memory location.
> It does, though, set the dirty flag in the page table, and Linux
> eventually inspects that flag and finds out that you have stored in the
> past.  At that time, it can call set_page_dirty.
>

Is there an existing interface to force it to check if the page is
dirty -- for example, one way to maintain coherency would be for my
normal read/write path to check if the page is dirty and write it back
and invalidate the page before executing the normal-path read/write.
This may be an unlikely scenerio, but I think it is one of the corner
cases fsx tickles.

    -eric