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From: Muchun Song <songmuchun@bytedance.com>
To: corbet@lwn.net, mike.kravetz@oracle.com, tglx@linutronix.de,
	mingo@redhat.com, bp@alien8.de, x86@kernel.org, hpa@zytor.com,
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	peterz@infradead.org, viro@zeniv.linux.org.uk,
	akpm@linux-foundation.org, paulmck@kernel.org,
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	almasrymina@google.com, rientjes@google.com, willy@infradead.org,
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	david@redhat.com, naoya.horiguchi@nec.com,
	joao.m.martins@oracle.com
Cc: duanxiongchun@bytedance.com, fam.zheng@bytedance.com,
	linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-mm@kvack.org, linux-fsdevel@vger.kernel.org,
	Muchun Song <songmuchun@bytedance.com>
Subject: [PATCH v20 5/9] mm: hugetlb: defer freeing of HugeTLB pages
Date: Thu, 15 Apr 2021 16:40:01 +0800
Message-ID: <20210415084005.25049-6-songmuchun@bytedance.com> (raw)
In-Reply-To: <20210415084005.25049-1-songmuchun@bytedance.com>

In the subsequent patch, we should allocate the vmemmap pages when
freeing a HugeTLB page. But update_and_free_page() can be called
under any context, so we cannot use GFP_KERNEL to allocate vmemmap
pages. However, we can defer the actual freeing in a kworker to
prevent from using GFP_ATOMIC to allocate the vmemmap pages.

The __update_and_free_page() is where the call to allocate vmemmmap
pages will be inserted.

Signed-off-by: Muchun Song <songmuchun@bytedance.com>
---
 mm/hugetlb.c         | 73 ++++++++++++++++++++++++++++++++++++++++++++++++----
 mm/hugetlb_vmemmap.c | 12 ---------
 mm/hugetlb_vmemmap.h | 17 ++++++++++++
 3 files changed, 85 insertions(+), 17 deletions(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 923d05e2806b..eeb8f5480170 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1376,7 +1376,7 @@ static void remove_hugetlb_page(struct hstate *h, struct page *page,
 	h->nr_huge_pages_node[nid]--;
 }
 
-static void update_and_free_page(struct hstate *h, struct page *page)
+static void __update_and_free_page(struct hstate *h, struct page *page)
 {
 	int i;
 	struct page *subpage = page;
@@ -1399,12 +1399,73 @@ static void update_and_free_page(struct hstate *h, struct page *page)
 	}
 }
 
+/*
+ * As update_and_free_page() can be called under any context, so we cannot
+ * use GFP_KERNEL to allocate vmemmap pages. However, we can defer the
+ * actual freeing in a workqueue to prevent from using GFP_ATOMIC to allocate
+ * the vmemmap pages.
+ *
+ * free_hpage_workfn() locklessly retrieves the linked list of pages to be
+ * freed and frees them one-by-one. As the page->mapping pointer is going
+ * to be cleared in free_hpage_workfn() anyway, it is reused as the llist_node
+ * structure of a lockless linked list of huge pages to be freed.
+ */
+static LLIST_HEAD(hpage_freelist);
+
+static void free_hpage_workfn(struct work_struct *work)
+{
+	struct llist_node *node;
+
+	node = llist_del_all(&hpage_freelist);
+
+	while (node) {
+		struct page *page;
+		struct hstate *h;
+
+		page = container_of((struct address_space **)node,
+				     struct page, mapping);
+		node = node->next;
+		page->mapping = NULL;
+		h = page_hstate(page);
+
+		__update_and_free_page(h, page);
+
+		cond_resched();
+	}
+}
+static DECLARE_WORK(free_hpage_work, free_hpage_workfn);
+
+static inline void flush_free_hpage_work(struct hstate *h)
+{
+	if (free_vmemmap_pages_per_hpage(h))
+		flush_work(&free_hpage_work);
+}
+
+static void update_and_free_page(struct hstate *h, struct page *page,
+				 bool atomic)
+{
+	if (!free_vmemmap_pages_per_hpage(h) || !atomic) {
+		__update_and_free_page(h, page);
+		return;
+	}
+
+	/*
+	 * Defer freeing to avoid using GFP_ATOMIC to allocate vmemmap pages.
+	 *
+	 * Only call schedule_work() if hpage_freelist is previously
+	 * empty. Otherwise, schedule_work() had been called but the workfn
+	 * hasn't retrieved the list yet.
+	 */
+	if (llist_add((struct llist_node *)&page->mapping, &hpage_freelist))
+		schedule_work(&free_hpage_work);
+}
+
 static void update_and_free_pages_bulk(struct hstate *h, struct list_head *list)
 {
 	struct page *page, *t_page;
 
 	list_for_each_entry_safe(page, t_page, list, lru) {
-		update_and_free_page(h, page);
+		update_and_free_page(h, page, false);
 		cond_resched();
 	}
 }
@@ -1471,12 +1532,12 @@ void free_huge_page(struct page *page)
 	if (HPageTemporary(page)) {
 		remove_hugetlb_page(h, page, false);
 		spin_unlock_irqrestore(&hugetlb_lock, flags);
-		update_and_free_page(h, page);
+		update_and_free_page(h, page, true);
 	} else if (h->surplus_huge_pages_node[nid]) {
 		/* remove the page from active list */
 		remove_hugetlb_page(h, page, true);
 		spin_unlock_irqrestore(&hugetlb_lock, flags);
-		update_and_free_page(h, page);
+		update_and_free_page(h, page, true);
 	} else {
 		arch_clear_hugepage_flags(page);
 		enqueue_huge_page(h, page);
@@ -1785,7 +1846,7 @@ int dissolve_free_huge_page(struct page *page)
 		remove_hugetlb_page(h, page, false);
 		h->max_huge_pages--;
 		spin_unlock_irq(&hugetlb_lock);
-		update_and_free_page(h, head);
+		update_and_free_page(h, head, false);
 		return 0;
 	}
 out:
@@ -2627,6 +2688,7 @@ static int set_max_huge_pages(struct hstate *h, unsigned long count, int nid,
 	 * pages in hstate via the proc/sysfs interfaces.
 	 */
 	mutex_lock(&h->resize_lock);
+	flush_free_hpage_work(h);
 	spin_lock_irq(&hugetlb_lock);
 
 	/*
@@ -2736,6 +2798,7 @@ static int set_max_huge_pages(struct hstate *h, unsigned long count, int nid,
 	/* free the pages after dropping lock */
 	spin_unlock_irq(&hugetlb_lock);
 	update_and_free_pages_bulk(h, &page_list);
+	flush_free_hpage_work(h);
 	spin_lock_irq(&hugetlb_lock);
 
 	while (count < persistent_huge_pages(h)) {
diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
index e45a138a7f85..cb28c5b6c9ff 100644
--- a/mm/hugetlb_vmemmap.c
+++ b/mm/hugetlb_vmemmap.c
@@ -180,18 +180,6 @@
 #define RESERVE_VMEMMAP_NR		2U
 #define RESERVE_VMEMMAP_SIZE		(RESERVE_VMEMMAP_NR << PAGE_SHIFT)
 
-/*
- * How many vmemmap pages associated with a HugeTLB page that can be freed
- * to the buddy allocator.
- *
- * Todo: Returns zero for now, which means the feature is disabled. We will
- * enable it once all the infrastructure is there.
- */
-static inline unsigned int free_vmemmap_pages_per_hpage(struct hstate *h)
-{
-	return 0;
-}
-
 static inline unsigned long free_vmemmap_pages_size_per_hpage(struct hstate *h)
 {
 	return (unsigned long)free_vmemmap_pages_per_hpage(h) << PAGE_SHIFT;
diff --git a/mm/hugetlb_vmemmap.h b/mm/hugetlb_vmemmap.h
index 6923f03534d5..01f8637adbe0 100644
--- a/mm/hugetlb_vmemmap.h
+++ b/mm/hugetlb_vmemmap.h
@@ -12,9 +12,26 @@
 
 #ifdef CONFIG_HUGETLB_PAGE_FREE_VMEMMAP
 void free_huge_page_vmemmap(struct hstate *h, struct page *head);
+
+/*
+ * How many vmemmap pages associated with a HugeTLB page that can be freed
+ * to the buddy allocator.
+ *
+ * Todo: Returns zero for now, which means the feature is disabled. We will
+ * enable it once all the infrastructure is there.
+ */
+static inline unsigned int free_vmemmap_pages_per_hpage(struct hstate *h)
+{
+	return 0;
+}
 #else
 static inline void free_huge_page_vmemmap(struct hstate *h, struct page *head)
 {
 }
+
+static inline unsigned int free_vmemmap_pages_per_hpage(struct hstate *h)
+{
+	return 0;
+}
 #endif /* CONFIG_HUGETLB_PAGE_FREE_VMEMMAP */
 #endif /* _LINUX_HUGETLB_VMEMMAP_H */
-- 
2.11.0


  parent reply index

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-15  8:39 [PATCH v20 0/9] Free some vmemmap pages of HugeTLB page Muchun Song
2021-04-15  8:39 ` [PATCH v20 1/9] mm: memory_hotplug: factor out bootmem core functions to bootmem_info.c Muchun Song
2021-04-15  8:39 ` [PATCH v20 2/9] mm: hugetlb: introduce a new config HUGETLB_PAGE_FREE_VMEMMAP Muchun Song
2021-04-15  8:39 ` [PATCH v20 3/9] mm: hugetlb: gather discrete indexes of tail page Muchun Song
2021-04-16 18:54   ` Mike Kravetz
2021-04-15  8:40 ` [PATCH v20 4/9] mm: hugetlb: free the vmemmap pages associated with each HugeTLB page Muchun Song
2021-04-16 21:10   ` Mike Kravetz
2021-04-17  2:55     ` [External] " Muchun Song
2021-04-15  8:40 ` Muchun Song [this message]
2021-04-16 23:55   ` [PATCH v20 5/9] mm: hugetlb: defer freeing of HugeTLB pages Mike Kravetz
2021-04-17  4:13     ` [External] " Muchun Song
2021-04-15  8:40 ` [PATCH v20 6/9] mm: hugetlb: alloc the vmemmap pages associated with each HugeTLB page Muchun Song
2021-04-19 23:19   ` Mike Kravetz
2021-04-20  8:46     ` [External] " Muchun Song
2021-04-20 17:48       ` Mike Kravetz
2021-04-21  3:42         ` Muchun Song
2021-04-15  8:40 ` [PATCH v20 7/9] mm: hugetlb: add a kernel parameter hugetlb_free_vmemmap Muchun Song
2021-04-19 23:41   ` Mike Kravetz
2021-04-15  8:40 ` [PATCH v20 8/9] mm: memory_hotplug: disable memmap_on_memory when hugetlb_free_vmemmap enabled Muchun Song
2021-04-20 10:35   ` Oscar Salvador
2021-04-21  3:41     ` [External] " Muchun Song
2021-04-21  7:33       ` Oscar Salvador
2021-04-21  9:06         ` Muchun Song
2021-04-15  8:40 ` [PATCH v20 9/9] mm: hugetlb: introduce nr_free_vmemmap_pages in the struct hstate Muchun Song

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