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SubjectRe: [PATCH][1/2]page_fault retry with NOPAGE_RETRY


On Fri, 10 Apr 2009, Wu Fengguang wrote:

> On Fri, Apr 10, 2009 at 02:02:05PM +0800, Andrew Morton wrote:
>
> > Can we please redo this as:
> >
> >
> > int write;
> > unsigned int flags;
> >
> > /*
> > * Big fat comment explaining the next three lines goes here
> > */
>
> Basically it's doing a
> (is_write_access | FAULT_FLAG_RETRY) =>
> (FAULT_FLAG_WRITE | FAULT_FLAG_RETRY)
> by extracting the bool part:
> > write = write_access & ~FAULT_FLAG_RETRY;
> convert bool to a bit flag:
> > unsigned int flags = (write ? FAULT_FLAG_WRITE : 0);

The point is, we shouldn't do that.

Your code is confused, because it uses "write_access" as if it had the old
behaviour (boolean to say "write") _plus_ the new behavior (bitmask to say
"retry"), and that's just wrong.

Just get rid of "write_access" entirely, and switch it over to something
that is a pure bitmask.

Yes, it means a couple of new preliminary patches that switch all callers
of handle_mm_fault() over to using the VM_FLAGS, but that's not a big
deal.

I'm following up this email with two _example_ patches. They are untested,
but they look sane. I'd like the series to _start_ with these, and then
you can pass FAULT_FLAGS_WRITE | FAULT_FLAGS_RETRY down to
handle_mm_fault() cleanly.
Hmm? Note the _untested_ part on the patches to follow. It was done very
mechanically, and the patches look sane, but .. !!!

Linus


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