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

[Andrew Morton]

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