On Mon, Apr 08, 2013 at 04:57:44PM -0400, KOSAKI Motohiro wrote:
> > - if (absent ||
> > + /*
> > + * is_swap_pte test covers both is_hugetlb_entry_hwpoisoned
> > + * and hugepages under migration in which case
> > + * hugetlb_fault waits for the migration and bails out
> > + * properly for HWPosined pages.
> > + */
> > + if (absent || is_swap_pte(huge_ptep_get(pte)) ||
> > ((flags & FOLL_WRITE) &&
> > !pte_write(huge_ptep_get(pte)))) {
> > int ret;
>
> Your comment describe what the code is. However we want the comment describe
> why. In migration case, calling hugetlb_fault() is natural. but in
> hwpoison case, it is
> needed more explanation.
We should call hugetlb_fault() when we encounter any kind of swap
type entry. It's consistent with handling of normal pages.
> Why can't we call is_hugetlb_hwpoisoned() directly?
We can use it, but I like to make code simple.
I rewrite the comment here, how about this?
- if (absent ||
+ /*
+ * We need call hugetlb_fault for both hugepages under migration
+ * (in which case hugetlb_fault waits for the migration,) and
+ * hwpoisoned hugepages (in which case we need to prevent the
+ * caller from accessing to them.) In order to do this, we use
+ * here is_swap_pte instead of is_hugetlb_entry_migration and
+ * is_hugetlb_entry_hwpoisoned. This is because it simply covers
+ * both cases, and because we can't follow correct pages
directly
+ * from any kind of swap entries.
+ */
+ if (absent || is_swap_pte(huge_ptep_get(pte)) ||
((flags & FOLL_WRITE) && !pte_write(huge_ptep_get(pte)))) {
int ret;
Thanks,
Naoya
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