Re: [patch 3/3] mm: fault handler to replace nopage and populate

Andrew Morton
2006-10-10T17:52:36Z

On Tue, 10 Oct 2006 14:13:27 +0200
Nick Piggin <npiggin@suse.de> wrote:

> On Tue, Oct 10, 2006 at 01:10:03PM +0100, Christoph Hellwig wrote:
> > On Sat, Oct 07, 2006 at 03:06:32PM +0200, Nick Piggin wrote:
> > > +/*
> > > + * fault_data is filled in the the pagefault handler and passed to the
> > > + * vma's ->fault function. That function is responsible for filling in
> > > + * 'type', which is the type of fault if a page is returned, or the type
> > > + * of error if NULL is returned.
> > > + */
> > > +struct fault_data {
> > > + struct vm_area_struct *vma;
> > > + unsigned long address;
> > > + pgoff_t pgoff;
> > > + unsigned int flags;
> > > +
> > > + int type;
> > > +};
> > >
> > > /*
> > > * These are the virtual MM functions - opening of an area, closing and
> > > @@ -203,6 +221,7 @@ extern pgprot_t protection_map[16];
> > > struct vm_operations_struct {
> > > void (*open)(struct vm_area_struct * area);
> > > void (*close)(struct vm_area_struct * area);
> > > + struct page * (*fault)(struct fault_data * data);
> >
> > Please pass the vma as an explicit first argument so that all vm_operations
> > operate on a vma. It's also much cleaner to have the separate between the
> > the object operated on (the vma) and all the fault details (struct fault_data).
>
> Hmm... I agree it is more consistent, but OTOH if we're passing a
> structure I thought it may as well just go in there. But I will
> change unless anyone comes up with an objection.

I'd agree that it's more attractive to have the vma* in the argument list,
but it presumably adds runtime cost: cycles and stack depth. I don't how
much though.