On Fri, Mar 11, 2011 at 03:04:10AM +0100, Andrea Arcangeli wrote:
> @@ -42,7 +42,7 @@ static pmd_t *get_old_pmd(struct mm_stru
>
> pmd = pmd_offset(pud, addr);
> split_huge_page_pmd(mm, pmd);
Wasn't getting rid of this line the sole purpose of the patch? :)
> - if (pmd_none_or_clear_bad(pmd))
> + if (pmd_none(*pmd))
> return NULL;
>
> return pmd;
[...]
> @@ -151,6 +148,23 @@ unsigned long move_page_tables(struct vm
> new_pmd = alloc_new_pmd(vma->vm_mm, vma, new_addr);
> if (!new_pmd)
> break;
> + if (pmd_trans_huge(*old_pmd)) {
> + int err = move_huge_pmd(vma, old_addr, new_addr,
> + old_end, old_pmd, new_pmd);
> + if (err > 0) {
> + old_addr += HPAGE_PMD_SIZE;
> + new_addr += HPAGE_PMD_SIZE;
> + continue;
> + }
> + }
> + /*
> + * split_huge_page_pmd() must run outside the
> + * pmd_trans_huge() block above because that check
> + * racy. split_huge_page_pmd() will recheck
> + * pmd_trans_huge() but in a not racy way under the
> + * page_table_lock.
> + */
> + split_huge_page_pmd(vma->vm_mm, old_pmd);
I don't understand what we are racing here against. If we see a huge
pmd, it may split. But we hold mmap_sem in write-mode, I don't see
how a regular pmd could become huge all of a sudden at this point.
Hannes
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