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SubjectRe: [PATCH v2 06/20] mm, hugetlb: return a reserved page to a reserved pool if failed
Date
Joonsoo Kim <iamjoonsoo.kim@lge.com> writes:

> If we fail with a reserved page, just calling put_page() is not sufficient,
> because put_page() invoke free_huge_page() at last step and it doesn't
> know whether a page comes from a reserved pool or not. So it doesn't do
> anything related to reserved count. This makes reserve count lower
> than how we need, because reserve count already decrease in
> dequeue_huge_page_vma(). This patch fix this situation.

You may want to document you are using PagePrivate for tracking
reservation and why it is ok to that.

>
> Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
>
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 6c8eec2..3f834f1 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -572,6 +572,7 @@ retry_cpuset:
> if (!vma_has_reserves(vma, chg))
> break;
>
> + SetPagePrivate(page);
> h->resv_huge_pages--;
> break;
> }
> @@ -626,15 +627,20 @@ static void free_huge_page(struct page *page)
> int nid = page_to_nid(page);
> struct hugepage_subpool *spool =
> (struct hugepage_subpool *)page_private(page);
> + bool restore_reserve;
>
> set_page_private(page, 0);
> page->mapping = NULL;
> BUG_ON(page_count(page));
> BUG_ON(page_mapcount(page));
> + restore_reserve = PagePrivate(page);
>
> spin_lock(&hugetlb_lock);
> hugetlb_cgroup_uncharge_page(hstate_index(h),
> pages_per_huge_page(h), page);
> + if (restore_reserve)
> + h->resv_huge_pages++;
> +
> if (h->surplus_huge_pages_node[nid] && huge_page_order(h) < MAX_ORDER) {
> /* remove the page from active list */
> list_del(&page->lru);
> @@ -2616,6 +2622,8 @@ retry_avoidcopy:
> spin_lock(&mm->page_table_lock);
> ptep = huge_pte_offset(mm, address & huge_page_mask(h));
> if (likely(pte_same(huge_ptep_get(ptep), pte))) {
> + ClearPagePrivate(new_page);
> +
> /* Break COW */
> huge_ptep_clear_flush(vma, address, ptep);
> set_huge_pte_at(mm, address, ptep,
> @@ -2727,6 +2735,7 @@ retry:
> goto retry;
> goto out;
> }
> + ClearPagePrivate(page);
>
> spin_lock(&inode->i_lock);
> inode->i_blocks += blocks_per_huge_page(h);
> @@ -2773,8 +2782,10 @@ retry:
> if (!huge_pte_none(huge_ptep_get(ptep)))
> goto backout;
>
> - if (anon_rmap)
> + if (anon_rmap) {
> + ClearPagePrivate(page);
> hugepage_add_new_anon_rmap(page, vma, address);
> + }
> else
> page_dup_rmap(page);
> new_pte = make_huge_pte(vma, page, ((vma->vm_flags & VM_WRITE)
> --
> 1.7.9.5



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