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SubjectRe: [PATCH 16/18] mm, hugetlb: return a reserved page to a reserved pool if failed
On Mon, Jul 29, 2013 at 02:32:07PM +0900, Joonsoo Kim wrote:
> 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.

I think we could use a page flag (for example PG_reserve) on a hugepage
in order to record that the hugepage comes from the reserved pool.
Furthermore, the reserve flag would be set when dequeueing a free hugepage,
and cleared when hugepage_fault returns, whether it fails or not.
I think it's simpler than put_page variant approach, but doesn't it work
to solve your problem?

Thanks,
Naoya Horiguchi

> Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
>
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index bb8a45f..6a9ec69 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -649,6 +649,34 @@ struct hstate *size_to_hstate(unsigned long size)
> return NULL;
> }
>
> +static void put_huge_page(struct page *page, int use_reserve)
> +{
> + struct hstate *h = page_hstate(page);
> + struct hugepage_subpool *spool =
> + (struct hugepage_subpool *)page_private(page);
> +
> + if (!use_reserve) {
> + put_page(page);
> + return;
> + }
> +
> + if (!put_page_testzero(page))
> + return;
> +
> + set_page_private(page, 0);
> + page->mapping = NULL;
> + BUG_ON(page_count(page));
> + BUG_ON(page_mapcount(page));
> +
> + spin_lock(&hugetlb_lock);
> + hugetlb_cgroup_uncharge_page(hstate_index(h),
> + pages_per_huge_page(h), page);
> + enqueue_huge_page(h, page);
> + h->resv_huge_pages++;
> + spin_unlock(&hugetlb_lock);
> + hugepage_subpool_put_pages(spool, 1);
> +}
> +
> static void free_huge_page(struct page *page)
> {
> /*
> @@ -2625,7 +2653,7 @@ retry_avoidcopy:
> spin_unlock(&mm->page_table_lock);
> mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
>
> - page_cache_release(new_page);
> + put_huge_page(new_page, use_reserve);
> out_old_page:
> page_cache_release(old_page);
> out_lock:
> @@ -2725,7 +2753,7 @@ retry:
>
> err = add_to_page_cache(page, mapping, idx, GFP_KERNEL);
> if (err) {
> - put_page(page);
> + put_huge_page(page, use_reserve);
> if (err == -EEXIST)
> goto retry;
> goto out;
> @@ -2798,7 +2826,7 @@ backout:
> spin_unlock(&mm->page_table_lock);
> backout_unlocked:
> unlock_page(page);
> - put_page(page);
> + put_huge_page(page, use_reserve);
> goto out;
> }
>
> --
> 1.7.9.5
>
> --
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