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Date: Tue, 6 Apr 2021 11:57:47 +0200
From: Michal Hocko <mhocko@...e.com>
To: Mike Kravetz <mike.kravetz@...cle.com>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org,
Roman Gushchin <guro@...com>,
Shakeel Butt <shakeelb@...gle.com>,
Oscar Salvador <osalvador@...e.de>,
David Hildenbrand <david@...hat.com>,
Muchun Song <songmuchun@...edance.com>,
David Rientjes <rientjes@...gle.com>,
Miaohe Lin <linmiaohe@...wei.com>,
Peter Zijlstra <peterz@...radead.org>,
Matthew Wilcox <willy@...radead.org>,
HORIGUCHI NAOYA <naoya.horiguchi@....com>,
"Aneesh Kumar K . V" <aneesh.kumar@...ux.ibm.com>,
Waiman Long <longman@...hat.com>, Peter Xu <peterx@...hat.com>,
Mina Almasry <almasrymina@...gle.com>,
Hillf Danton <hdanton@...a.com>,
Joonsoo Kim <iamjoonsoo.kim@....com>,
Barry Song <song.bao.hua@...ilicon.com>,
Will Deacon <will@...nel.org>,
Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v4 5/8] hugetlb: call update_and_free_page without
hugetlb_lock
On Mon 05-04-21 16:00:40, Mike Kravetz wrote:
> With the introduction of remove_hugetlb_page(), there is no need for
> update_and_free_page to hold the hugetlb lock. Change all callers to
> drop the lock before calling.
>
> With additional code modifications, this will allow loops which decrease
> the huge page pool to drop the hugetlb_lock with each page to reduce
> long hold times.
>
> The ugly unlock/lock cycle in free_pool_huge_page will be removed in
> a subsequent patch which restructures free_pool_huge_page.
>
> Signed-off-by: Mike Kravetz <mike.kravetz@...cle.com>
Still looks good.
Acked-by: Michal Hocko <mhocko@...e.com>
> ---
> mm/hugetlb.c | 43 +++++++++++++++++++++++++++++++++----------
> 1 file changed, 33 insertions(+), 10 deletions(-)
>
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index df2a3d1f632b..be6031a8e2a9 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -1446,16 +1446,18 @@ static void __free_huge_page(struct page *page)
>
> if (HPageTemporary(page)) {
> remove_hugetlb_page(h, page, false);
> + spin_unlock(&hugetlb_lock);
> update_and_free_page(h, page);
> } else if (h->surplus_huge_pages_node[nid]) {
> /* remove the page from active list */
> remove_hugetlb_page(h, page, true);
> + spin_unlock(&hugetlb_lock);
> update_and_free_page(h, page);
> } else {
> arch_clear_hugepage_flags(page);
> enqueue_huge_page(h, page);
> + spin_unlock(&hugetlb_lock);
> }
> - spin_unlock(&hugetlb_lock);
> }
>
> /*
> @@ -1736,7 +1738,13 @@ static int free_pool_huge_page(struct hstate *h, nodemask_t *nodes_allowed,
> list_entry(h->hugepage_freelists[node].next,
> struct page, lru);
> remove_hugetlb_page(h, page, acct_surplus);
> + /*
> + * unlock/lock around update_and_free_page is temporary
> + * and will be removed with subsequent patch.
> + */
> + spin_unlock(&hugetlb_lock);
> update_and_free_page(h, page);
> + spin_lock(&hugetlb_lock);
> ret = 1;
> break;
> }
> @@ -1805,8 +1813,9 @@ int dissolve_free_huge_page(struct page *page)
> }
> remove_hugetlb_page(h, page, false);
> h->max_huge_pages--;
> + spin_unlock(&hugetlb_lock);
> update_and_free_page(h, head);
> - rc = 0;
> + return 0;
> }
> out:
> spin_unlock(&hugetlb_lock);
> @@ -2291,6 +2300,7 @@ static int alloc_and_dissolve_huge_page(struct hstate *h, struct page *old_page,
> gfp_t gfp_mask = htlb_alloc_mask(h) | __GFP_THISNODE;
> int nid = page_to_nid(old_page);
> struct page *new_page;
> + struct page *page_to_free;
> int ret = 0;
>
> /*
> @@ -2313,16 +2323,16 @@ static int alloc_and_dissolve_huge_page(struct hstate *h, struct page *old_page,
> * Freed from under us. Drop new_page too.
> */
> remove_hugetlb_page(h, new_page, false);
> - update_and_free_page(h, new_page);
> - goto unlock;
> + page_to_free = new_page;
> + goto unlock_free;
> } else if (page_count(old_page)) {
> /*
> * Someone has grabbed the page, try to isolate it here.
> * Fail with -EBUSY if not possible.
> */
> remove_hugetlb_page(h, new_page, false);
> - update_and_free_page(h, new_page);
> spin_unlock(&hugetlb_lock);
> + update_and_free_page(h, new_page);
> if (!isolate_huge_page(old_page, list))
> ret = -EBUSY;
> return ret;
> @@ -2344,11 +2354,12 @@ static int alloc_and_dissolve_huge_page(struct hstate *h, struct page *old_page,
> * enqueue_huge_page for new page. Net result is no change.
> */
> remove_hugetlb_page(h, old_page, false);
> - update_and_free_page(h, old_page);
> enqueue_huge_page(h, new_page);
> + page_to_free = old_page;
> }
> -unlock:
> +unlock_free:
> spin_unlock(&hugetlb_lock);
> + update_and_free_page(h, page_to_free);
>
> return ret;
> }
> @@ -2671,22 +2682,34 @@ static void try_to_free_low(struct hstate *h, unsigned long count,
> nodemask_t *nodes_allowed)
> {
> int i;
> + struct page *page, *next;
> + LIST_HEAD(page_list);
>
> if (hstate_is_gigantic(h))
> return;
>
> + /*
> + * Collect pages to be freed on a list, and free after dropping lock
> + */
> for_each_node_mask(i, *nodes_allowed) {
> - struct page *page, *next;
> struct list_head *freel = &h->hugepage_freelists[i];
> list_for_each_entry_safe(page, next, freel, lru) {
> if (count >= h->nr_huge_pages)
> - return;
> + goto out;
> if (PageHighMem(page))
> continue;
> remove_hugetlb_page(h, page, false);
> - update_and_free_page(h, page);
> + list_add(&page->lru, &page_list);
> }
> }
> +
> +out:
> + spin_unlock(&hugetlb_lock);
> + list_for_each_entry_safe(page, next, &page_list, lru) {
> + update_and_free_page(h, page);
> + cond_resched();
> + }
> + spin_lock(&hugetlb_lock);
> }
> #else
> static inline void try_to_free_low(struct hstate *h, unsigned long count,
> --
> 2.30.2
>
--
Michal Hocko
SUSE Labs
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