mm: hugetlb: introduce nr_free_vmemmap_pages in the struct hstate

All the infrastructure is ready, so we introduce nr_free_vmemmap_pages
field in the hstate to indicate how many vmemmap pages associated with a
HugeTLB page that can be freed to buddy allocator.  And initialize it in
the hugetlb_vmemmap_init().  This patch is actual enablement of the
feature.

There are only (RESERVE_VMEMMAP_SIZE / sizeof(struct page)) struct page
structs that can be used when CONFIG_HUGETLB_PAGE_FREE_VMEMMAP, so add a
BUILD_BUG_ON to catch invalid usage of the tail struct page.

Link: https://lkml.kernel.org/r/20210510030027.56044-10-songmuchun@bytedance.com
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Acked-by: Mike Kravetz <mike.kravetz@oracle.com>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
Reviewed-by: Miaohe Lin <linmiaohe@huawei.com>
Tested-by: Chen Huang <chenhuang5@huawei.com>
Tested-by: Bodeddula Balasubramaniam <bodeddub@amazon.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Balbir Singh <bsingharora@gmail.com>
Cc: Barry Song <song.bao.hua@hisilicon.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: David Rientjes <rientjes@google.com>
Cc: HORIGUCHI NAOYA <naoya.horiguchi@nec.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Joao Martins <joao.m.martins@oracle.com>
Cc: Joerg Roedel <jroedel@suse.de>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mina Almasry <almasrymina@google.com>
Cc: Oliver Neukum <oneukum@suse.com>
Cc: Paul E. McKenney <paulmck@kernel.org>
Cc: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Xiongchun Duan <duanxiongchun@bytedance.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index 9ad9984..8c19208 100644 (file)
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -608,6 +608,9 @@ struct hstate {
        unsigned int nr_huge_pages_node[MAX_NUMNODES];
        unsigned int free_huge_pages_node[MAX_NUMNODES];
        unsigned int surplus_huge_pages_node[MAX_NUMNODES];
+#ifdef CONFIG_HUGETLB_PAGE_FREE_VMEMMAP
+       unsigned int nr_free_vmemmap_pages;
+#endif
 #ifdef CONFIG_CGROUP_HUGETLB
        /* cgroup control files */
        struct cftype cgroup_files_dfl[7];

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 778db5d..dd9c90c 100644 (file)
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -3585,6 +3585,7 @@ void __init hugetlb_add_hstate(unsigned int order)
        h->next_nid_to_free = first_memory_node;
        snprintf(h->name, HSTATE_NAME_LEN, "hugepages-%lukB",
                                        huge_page_size(h)/1024);
+       hugetlb_vmemmap_init(h);
 
        parsed_hstate = h;
 }

diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
index 3070e14..f9f9bb2 100644 (file)
--- a/mm/hugetlb_vmemmap.c
+++ b/mm/hugetlb_vmemmap.c
@@ -262,3 +262,36 @@ void free_huge_page_vmemmap(struct hstate *h, struct page *head)
 
        SetHPageVmemmapOptimized(head);
 }
+
+void __init hugetlb_vmemmap_init(struct hstate *h)
+{
+       unsigned int nr_pages = pages_per_huge_page(h);
+       unsigned int vmemmap_pages;
+
+       /*
+        * There are only (RESERVE_VMEMMAP_SIZE / sizeof(struct page)) struct
+        * page structs that can be used when CONFIG_HUGETLB_PAGE_FREE_VMEMMAP,
+        * so add a BUILD_BUG_ON to catch invalid usage of the tail struct page.
+        */
+       BUILD_BUG_ON(__NR_USED_SUBPAGE >=
+                    RESERVE_VMEMMAP_SIZE / sizeof(struct page));
+
+       if (!hugetlb_free_vmemmap_enabled)
+               return;
+
+       vmemmap_pages = (nr_pages * sizeof(struct page)) >> PAGE_SHIFT;
+       /*
+        * The head page and the first tail page are not to be freed to buddy
+        * allocator, the other pages will map to the first tail page, so they
+        * can be freed.
+        *
+        * Could RESERVE_VMEMMAP_NR be greater than @vmemmap_pages? It is true
+        * on some architectures (e.g. aarch64). See Documentation/arm64/
+        * hugetlbpage.rst for more details.
+        */
+       if (likely(vmemmap_pages > RESERVE_VMEMMAP_NR))
+               h->nr_free_vmemmap_pages = vmemmap_pages - RESERVE_VMEMMAP_NR;
+
+       pr_info("can free %d vmemmap pages for %s\n", h->nr_free_vmemmap_pages,
+               h->name);
+}

diff --git a/mm/hugetlb_vmemmap.h b/mm/hugetlb_vmemmap.h
index a37771b..cb2bef8 100644 (file)
--- a/mm/hugetlb_vmemmap.h
+++ b/mm/hugetlb_vmemmap.h
@@ -13,17 +13,15 @@
 #ifdef CONFIG_HUGETLB_PAGE_FREE_VMEMMAP
 int alloc_huge_page_vmemmap(struct hstate *h, struct page *head);
 void free_huge_page_vmemmap(struct hstate *h, struct page *head);
+void hugetlb_vmemmap_init(struct hstate *h);
 
 /*
  * 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;
+       return h->nr_free_vmemmap_pages;
 }
 #else
 static inline int alloc_huge_page_vmemmap(struct hstate *h, struct page *head)
@@ -35,6 +33,10 @@ static inline void free_huge_page_vmemmap(struct hstate *h, struct page *head)
 {
 }
 
+static inline void hugetlb_vmemmap_init(struct hstate *h)
+{
+}
+
 static inline unsigned int free_vmemmap_pages_per_hpage(struct hstate *h)
 {
        return 0;