Re: [git pull] cpus4096 tree, part 3

Andrew Morton
2009-01-26T20:45:59Z

On Mon, 26 Jan 2009 21:09:57 +0100
Ingo Molnar <mingo@elte.hu> wrote:

> ...
>
> Btw., regarding pagefault retry. The bits that are in -mm currently i
> find a bit ugly:
>
> > +++ a/arch/x86/mm/fault.c
> > @@ -799,7 +799,7 @@ void __kprobes do_page_fault(struct pt_r
> > struct vm_area_struct *vma;
> > int write;
> > int fault;
> > - unsigned int retry_flag = FAULT_FLAG_RETRY;
> > + int retry_flag = 1;
> >
> > tsk = current;
> > mm = tsk->mm;
> > @@ -951,6 +951,7 @@ good_area:
> > }
> >
> > write |= retry_flag;
> > +
> > /*
> > * If for any reason at all we couldn't handle the fault,
> > * make sure we exit gracefully rather than endlessly redo
> > @@ -969,8 +970,8 @@ good_area:
> > * be removed or changed after the retry.
> > */
> > if (fault & VM_FAULT_RETRY) {
> > - if (write & FAULT_FLAG_RETRY) {
> > - retry_flag &= ~FAULT_FLAG_RETRY;
> > + if (retry_flag) {
> > + retry_flag = 0;
> > goto retry;
> > }
> > BUG();
>
> as this complicates every architecture with a 'can the fault be retried'
> logic and open-coded retry loop.
>
> But that logic is rather repetitive and once an architecture filters out
> all its special in-kernel sources of faults and the hw quirks it has, the
> handling of pte faults is rather generic and largely offloaded into
> handle_pte_fault() already.
>
> So when this patch was submitted a few weeks ago i suggested that retry
> should be done purely in mm/memory.c instead, and the low level code
> should at most be refactored to suit this method, but not complicated any
> further.
>
> Any deep reasons for why such a more generic approach is not desirable?
>

Let's cc the people who wrote it.