On Thu, 2008-03-13 at 10:12 +1100, Rusty Russell wrote:
> On Thursday 13 March 2008 00:21:33 Martin Schwidefsky wrote:
> > @@ -957,6 +975,19 @@ struct page *follow_page(struct vm_area_
> >
> > if (flags & FOLL_GET)
> > get_page(page);
> > +
> > + if (flags & FOLL_GET) {
> > + /*
> > + * The page is made stable if a reference is acquired.
> > + * If the caller does not get a reference it implies that
> > + * the caller can deal with page faults in case the page
> > + * is swapped out. In this case the caller can deal with
> > + * discard faults as well.
> > + */
> > + if (unlikely(!page_make_stable(page)))
> > + goto out_discard;
> > + }
>
> Dumb comment: seems like this if could be folded into the one above.
In this patch yes, but a later patch adds a condition:
- if (flags & FOLL_GET) {
+ if ((flags & FOLL_GET) || (vma->vm_flags & VM_LOCKED)) {
> > + * Attempts to change the state of a page to volatile.
> > + * If there is something preventing the state change the page stays
> > + * int its current state.
>
> Typo "int its current state".
Fixed.
> > return NULL;
> >
> > pte = pte_offset_map(pmd, address);
> > + ptl = pte_lockptr(mm, pmd);
> > /* Make a quick check before getting the lock */
> > +#ifndef CONFIG_PAGE_STATES
> > + /*
> > + * If the page table lock for this pte is taken we have to
> > + * assume that someone might be mapping the page. To solve
> > + * the race of a page discard vs. mapping the page we have
> > + * to serialize the two operations by taking the lock,
> > + * otherwise we end up with a pte for a page that has been
> > + * removed from page cache by the discard fault handler.
> > + */
> > + if (!spin_is_locked(ptl))
> > +#endif
> > if (!pte_present(*pte)) {
> > pte_unmap(pte);
> > return NULL;
> > }
> >
> > - ptl = pte_lockptr(mm, pmd);
> > spin_lock(ptl);
> > if (pte_present(*pte) && page_to_pfn(page) == pte_pfn(*pte)) {
> > *ptlp = ptl;
>
> Did you really mean ifndef here?
That is a major nit. This should be an #ifdef. In previous versions the
complete "if (!pte_present(*pte)) { }" is ifdefed, the later versions
use the !spin_is_locked condition. Only I forgot to invert the #ifndef.
Fixed.
> (BTW: I'm just reading through the code, not really understanding it, so
> this is not a real review).
I take the small review anytime. Already found one major nit.
--
blue skies,
Martin.
"Reality continues to ruin my life." - Calvin.
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