mm: hugetlb: free the vmemmap pages associated with each HugeTLB page

Every HugeTLB has more than one struct page structure.  We __know__ that
we only use the first 4 (__NR_USED_SUBPAGE) struct page structures to
store metadata associated with each HugeTLB.

There are a lot of struct page structures associated with each HugeTLB
page.  For tail pages, the value of compound_head is the same.  So we can
reuse first page of tail page structures.  We map the virtual addresses of
the remaining pages of tail page structures to the first tail page struct,
and then free these page frames.  Therefore, we need to reserve two pages
as vmemmap areas.

When we allocate a HugeTLB page from the buddy, we can free some vmemmap
pages associated with each HugeTLB page.  It is more appropriate to do it
in the prep_new_huge_page().

The free_vmemmap_pages_per_hpage(), which indicates how many vmemmap pages
associated with a HugeTLB page can be freed, returns zero for now, which
means the feature is disabled.  We will enable it once all the
infrastructure is there.

[willy@infradead.org: fix documentation warning]
  Link: https://lkml.kernel.org/r/20210615200242.1716568-5-willy@infradead.org

Link: https://lkml.kernel.org/r/20210510030027.56044-5-songmuchun@bytedance.com
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
Tested-by: Chen Huang <chenhuang5@huawei.com>
Tested-by: Bodeddula Balasubramaniam <bodeddub@amazon.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Reviewed-by: Mike Kravetz <mike.kravetz@oracle.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: Miaohe Lin <linmiaohe@huawei.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>

1 files changed, 194 insertions, 0 deletions

diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c
index 16183d85a7d5..3ec5488c815c 100644
--- a/mm/sparse-vmemmap.c
+++ b/mm/sparse-vmemmap.c
@@ -27,8 +27,202 @@
 #include <linux/spinlock.h>
 #include <linux/vmalloc.h>
 #include <linux/sched.h>
+#include <linux/pgtable.h>
+#include <linux/bootmem_info.h>
+
 #include <asm/dma.h>
 #include <asm/pgalloc.h>
+#include <asm/tlbflush.h>
+
+/**
+ * struct vmemmap_remap_walk - walk vmemmap page table
+ *
+ * @remap_pte:		called for each lowest-level entry (PTE).
+ * @reuse_page:		the page which is reused for the tail vmemmap pages.
+ * @reuse_addr:		the virtual address of the @reuse_page page.
+ * @vmemmap_pages:	the list head of the vmemmap pages that can be freed.
+ */
+struct vmemmap_remap_walk {
+	void (*remap_pte)(pte_t *pte, unsigned long addr,
+			  struct vmemmap_remap_walk *walk);
+	struct page *reuse_page;
+	unsigned long reuse_addr;
+	struct list_head *vmemmap_pages;
+};
+
+static void vmemmap_pte_range(pmd_t *pmd, unsigned long addr,
+			      unsigned long end,
+			      struct vmemmap_remap_walk *walk)
+{
+	pte_t *pte = pte_offset_kernel(pmd, addr);
+
+	/*
+	 * The reuse_page is found 'first' in table walk before we start
+	 * remapping (which is calling @walk->remap_pte).
+	 */
+	if (!walk->reuse_page) {
+		walk->reuse_page = pte_page(*pte);
+		/*
+		 * Because the reuse address is part of the range that we are
+		 * walking, skip the reuse address range.
+		 */
+		addr += PAGE_SIZE;
+		pte++;
+	}
+
+	for (; addr != end; addr += PAGE_SIZE, pte++)
+		walk->remap_pte(pte, addr, walk);
+}
+
+static void vmemmap_pmd_range(pud_t *pud, unsigned long addr,
+			      unsigned long end,
+			      struct vmemmap_remap_walk *walk)
+{
+	pmd_t *pmd;
+	unsigned long next;
+
+	pmd = pmd_offset(pud, addr);
+	do {
+		BUG_ON(pmd_leaf(*pmd));
+
+		next = pmd_addr_end(addr, end);
+		vmemmap_pte_range(pmd, addr, next, walk);
+	} while (pmd++, addr = next, addr != end);
+}
+
+static void vmemmap_pud_range(p4d_t *p4d, unsigned long addr,
+			      unsigned long end,
+			      struct vmemmap_remap_walk *walk)
+{
+	pud_t *pud;
+	unsigned long next;
+
+	pud = pud_offset(p4d, addr);
+	do {
+		next = pud_addr_end(addr, end);
+		vmemmap_pmd_range(pud, addr, next, walk);
+	} while (pud++, addr = next, addr != end);
+}
+
+static void vmemmap_p4d_range(pgd_t *pgd, unsigned long addr,
+			      unsigned long end,
+			      struct vmemmap_remap_walk *walk)
+{
+	p4d_t *p4d;
+	unsigned long next;
+
+	p4d = p4d_offset(pgd, addr);
+	do {
+		next = p4d_addr_end(addr, end);
+		vmemmap_pud_range(p4d, addr, next, walk);
+	} while (p4d++, addr = next, addr != end);
+}
+
+static void vmemmap_remap_range(unsigned long start, unsigned long end,
+				struct vmemmap_remap_walk *walk)
+{
+	unsigned long addr = start;
+	unsigned long next;
+	pgd_t *pgd;
+
+	VM_BUG_ON(!IS_ALIGNED(start, PAGE_SIZE));
+	VM_BUG_ON(!IS_ALIGNED(end, PAGE_SIZE));
+
+	pgd = pgd_offset_k(addr);
+	do {
+		next = pgd_addr_end(addr, end);
+		vmemmap_p4d_range(pgd, addr, next, walk);
+	} while (pgd++, addr = next, addr != end);
+
+	/*
+	 * We only change the mapping of the vmemmap virtual address range
+	 * [@start + PAGE_SIZE, end), so we only need to flush the TLB which
+	 * belongs to the range.
+	 */
+	flush_tlb_kernel_range(start + PAGE_SIZE, end);
+}
+
+/*
+ * Free a vmemmap page. A vmemmap page can be allocated from the memblock
+ * allocator or buddy allocator. If the PG_reserved flag is set, it means
+ * that it allocated from the memblock allocator, just free it via the
+ * free_bootmem_page(). Otherwise, use __free_page().
+ */
+static inline void free_vmemmap_page(struct page *page)
+{
+	if (PageReserved(page))
+		free_bootmem_page(page);
+	else
+		__free_page(page);
+}
+
+/* Free a list of the vmemmap pages */
+static void free_vmemmap_page_list(struct list_head *list)
+{
+	struct page *page, *next;
+
+	list_for_each_entry_safe(page, next, list, lru) {
+		list_del(&page->lru);
+		free_vmemmap_page(page);
+	}
+}
+
+static void vmemmap_remap_pte(pte_t *pte, unsigned long addr,
+			      struct vmemmap_remap_walk *walk)
+{
+	/*
+	 * Remap the tail pages as read-only to catch illegal write operation
+	 * to the tail pages.
+	 */
+	pgprot_t pgprot = PAGE_KERNEL_RO;
+	pte_t entry = mk_pte(walk->reuse_page, pgprot);
+	struct page *page = pte_page(*pte);
+
+	list_add(&page->lru, walk->vmemmap_pages);
+	set_pte_at(&init_mm, addr, pte, entry);
+}
+
+/**
+ * vmemmap_remap_free - remap the vmemmap virtual address range [@start, @end)
+ *			to the page which @reuse is mapped to, then free vmemmap
+ *			which the range are mapped to.
+ * @start:	start address of the vmemmap virtual address range that we want
+ *		to remap.
+ * @end:	end address of the vmemmap virtual address range that we want to
+ *		remap.
+ * @reuse:	reuse address.
+ *
+ * Note: This function depends on vmemmap being base page mapped. Please make
+ * sure that we disable PMD mapping of vmemmap pages when calling this function.
+ */
+void vmemmap_remap_free(unsigned long start, unsigned long end,
+			unsigned long reuse)
+{
+	LIST_HEAD(vmemmap_pages);
+	struct vmemmap_remap_walk walk = {
+		.remap_pte	= vmemmap_remap_pte,
+		.reuse_addr	= reuse,
+		.vmemmap_pages	= &vmemmap_pages,
+	};
+
+	/*
+	 * In order to make remapping routine most efficient for the huge pages,
+	 * the routine of vmemmap page table walking has the following rules
+	 * (see more details from the vmemmap_pte_range()):
+	 *
+	 * - The range [@start, @end) and the range [@reuse, @reuse + PAGE_SIZE)
+	 *   should be continuous.
+	 * - The @reuse address is part of the range [@reuse, @end) that we are
+	 *   walking which is passed to vmemmap_remap_range().
+	 * - The @reuse address is the first in the complete range.
+	 *
+	 * So we need to make sure that @start and @reuse meet the above rules.
+	 */
+	BUG_ON(start - reuse != PAGE_SIZE);
+
+	vmemmap_remap_range(reuse, end, &walk);
+	free_vmemmap_page_list(&vmemmap_pages);
+}
 
 /*
  * Allocate a block of memory to be used to back the virtual memory map