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SubjectRe: [PATCH][1/2]page_fault retry with NOPAGE_RETRY
On Fri, Apr 10, 2009 at 02:02:05PM +0800, Andrew Morton wrote:
[snip]
> > if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE)))
> > return ret;
> >
> > @@ -2611,8 +2618,10 @@ static int do_linear_fault(struct mm_struct *mm, struct
> > {
> > pgoff_t pgoff = (((address & PAGE_MASK)
> > - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;
> > - unsigned int flags = (write_access ? FAULT_FLAG_WRITE : 0);
> > + int write = write_access & ~FAULT_FLAG_RETRY;
> > + unsigned int flags = (write ? FAULT_FLAG_WRITE : 0);
> >
> > + flags |= (write_access & FAULT_FLAG_RETRY);
>
> gee, I'm lost.

So did me.

> 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);
and restore the FAULT_FLAG_RETRY:
> flags |= (write_access & FAULT_FLAG_RETRY);
Thanks,
Fengguang



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