Re: memory unplug v4 intro [1/6] migration without mm->sem

[Christoph Lameter <clameter@sgi.com>]

On Fri, 8 Jun 2007, KAMEZAWA Hiroyuki wrote:

> On Thu, 7 Jun 2007 22:47:08 -0700 (PDT)
> Christoph Lameter <clameter@sgi.com> wrote:
> 
> > >  static inline void anon_vma_lock(struct vm_area_struct *vma)
> > >  {
> > >  	struct anon_vma *anon_vma = vma->anon_vma;
> > 
> > Could you fold as much as possible into mm/migrate.c?
> > 
> Ah, maybe ok. But scattering codes around rmap in several files is ok ?

No. Lets try to keep the changes to rmap minimal.

> > Could you avoid these checks by having page_referend_one fail
> > appropriately on the dummy vma?
> > 
> Hmm, Is this better ?
> ==
> static int page_referenced_one(struct page *page,
>         struct vm_area_struct *vma, unsigned int *mapcount)
> {
>         struct mm_struct *mm = vma->vm_mm;
>         unsigned long address;
>         pte_t *pte;
>         spinlock_t *ptl;
>         int referenced = 0;
> 
> +	if(is_dummy_vma(vma))
> +		return 0;

The best solution would be if you could fill the dummy vma with such 
values that will give you the intended result without having to modify 
page_referenced_one. If you can make vma_address() fail then you have 
what you want. F.e. setting vma->vm_end to zero should do it. (is it not 
already zero?)

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