+ hugetlb-batch-freeing-of-vmemmap-pages.patch added to mm-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: hugetlb: batch freeing of vmemmap pages
has been added to the -mm mm-unstable branch.  Its filename is
     hugetlb-batch-freeing-of-vmemmap-pages.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/hugetlb-batch-freeing-of-vmemmap-pages.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Mike Kravetz <mike.kravetz@oracle.com>
Subject: hugetlb: batch freeing of vmemmap pages
Date: Fri, 15 Sep 2023 15:15:42 -0700

Now that batching of hugetlb vmemmap optimization processing is possible,
batch the freeing of vmemmap pages.  When freeing vmemmap pages for a
hugetlb page, we add them to a list that is freed after the entire batch
has been processed.

This enhances the ability to return contiguous ranges of memory to the low
level allocators.

Link: https://lkml.kernel.org/r/20230915221548.552084-10-mike.kravetz@oracle.com
Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: David Rientjes <rientjes@google.com>
Cc: James Houghton <jthoughton@google.com>
Cc: Joao Martins <joao.m.martins@oracle.com>
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Muchun Song <songmuchun@bytedance.com>
Cc: Naoya Horiguchi <naoya.horiguchi@linux.dev>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Sidhartha Kumar <sidhartha.kumar@oracle.com>
Cc: Xiongchun Duan <duanxiongchun@bytedance.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/hugetlb_vmemmap.c |   85 ++++++++++++++++++++++++++++-------------
 1 file changed, 59 insertions(+), 26 deletions(-)

--- a/mm/hugetlb_vmemmap.c~hugetlb-batch-freeing-of-vmemmap-pages
+++ a/mm/hugetlb_vmemmap.c
@@ -222,6 +222,9 @@ static void free_vmemmap_page_list(struc
 {
 	struct page *page, *next;
 
+	if (list_empty(list))
+		return;
+
 	list_for_each_entry_safe(page, next, list, lru)
 		free_vmemmap_page(page);
 }
@@ -251,7 +254,7 @@ static void vmemmap_remap_pte(pte_t *pte
 	}
 
 	entry = mk_pte(walk->reuse_page, pgprot);
-	list_add_tail(&page->lru, walk->vmemmap_pages);
+	list_add(&page->lru, walk->vmemmap_pages);
 	set_pte_at(&init_mm, addr, pte, entry);
 }
 
@@ -306,18 +309,20 @@ static void vmemmap_restore_pte(pte_t *p
  * @end:	end address of the vmemmap virtual address range that we want to
  *		remap.
  * @reuse:	reuse address.
+ * @vmemmap_pages: list to deposit vmemmap pages to be freed.  It is callers
+ *		responsibility to free pages.
  *
  * Return: %0 on success, negative error code otherwise.
  */
 static int vmemmap_remap_free(unsigned long start, unsigned long end,
-			      unsigned long reuse)
+			      unsigned long reuse,
+			      struct list_head *vmemmap_pages)
 {
 	int ret;
-	LIST_HEAD(vmemmap_pages);
 	struct vmemmap_remap_walk walk = {
 		.remap_pte	= vmemmap_remap_pte,
 		.reuse_addr	= reuse,
-		.vmemmap_pages	= &vmemmap_pages,
+		.vmemmap_pages	= vmemmap_pages,
 	};
 	int nid = page_to_nid((struct page *)reuse);
 	gfp_t gfp_mask = GFP_KERNEL | __GFP_NORETRY | __GFP_NOWARN;
@@ -334,7 +339,7 @@ static int vmemmap_remap_free(unsigned l
 	if (walk.reuse_page) {
 		copy_page(page_to_virt(walk.reuse_page),
 			  (void *)walk.reuse_addr);
-		list_add(&walk.reuse_page->lru, &vmemmap_pages);
+		list_add(&walk.reuse_page->lru, vmemmap_pages);
 	}
 
 	/*
@@ -365,15 +370,13 @@ static int vmemmap_remap_free(unsigned l
 		walk = (struct vmemmap_remap_walk) {
 			.remap_pte	= vmemmap_restore_pte,
 			.reuse_addr	= reuse,
-			.vmemmap_pages	= &vmemmap_pages,
+			.vmemmap_pages	= vmemmap_pages,
 		};
 
 		vmemmap_remap_range(reuse, end, &walk);
 	}
 	mmap_read_unlock(&init_mm);
 
-	free_vmemmap_page_list(&vmemmap_pages);
-
 	return ret;
 }
 
@@ -389,7 +392,7 @@ static int alloc_vmemmap_page_list(unsig
 		page = alloc_pages_node(nid, gfp_mask, 0);
 		if (!page)
 			goto out;
-		list_add_tail(&page->lru, list);
+		list_add(&page->lru, list);
 	}
 
 	return 0;
@@ -576,24 +579,17 @@ static bool vmemmap_should_optimize(cons
 	return true;
 }
 
-/**
- * hugetlb_vmemmap_optimize - optimize @head page's vmemmap pages.
- * @h:		struct hstate.
- * @head:	the head page whose vmemmap pages will be optimized.
- *
- * This function only tries to optimize @head's vmemmap pages and does not
- * guarantee that the optimization will succeed after it returns. The caller
- * can use HPageVmemmapOptimized(@head) to detect if @head's vmemmap pages
- * have been optimized.
- */
-void hugetlb_vmemmap_optimize(const struct hstate *h, struct page *head)
+static int __hugetlb_vmemmap_optimize(const struct hstate *h,
+					struct page *head,
+					struct list_head *vmemmap_pages)
 {
+	int ret = 0;
 	unsigned long vmemmap_start = (unsigned long)head, vmemmap_end;
 	unsigned long vmemmap_reuse;
 
 	VM_WARN_ON_ONCE(!PageHuge(head));
 	if (!vmemmap_should_optimize(h, head))
-		return;
+		return ret;
 
 	static_branch_inc(&hugetlb_optimize_vmemmap_key);
 
@@ -603,21 +599,58 @@ void hugetlb_vmemmap_optimize(const stru
 
 	/*
 	 * Remap the vmemmap virtual address range [@vmemmap_start, @vmemmap_end)
-	 * to the page which @vmemmap_reuse is mapped to, then free the pages
-	 * which the range [@vmemmap_start, @vmemmap_end] is mapped to.
+	 * to the page which @vmemmap_reuse is mapped to.  Add pages previously
+	 * mapping the range to vmemmap_pages list so that they can be freed by
+	 * the caller.
 	 */
-	if (vmemmap_remap_free(vmemmap_start, vmemmap_end, vmemmap_reuse))
+	ret = vmemmap_remap_free(vmemmap_start, vmemmap_end, vmemmap_reuse, vmemmap_pages);
+	if (ret)
 		static_branch_dec(&hugetlb_optimize_vmemmap_key);
 	else
 		SetHPageVmemmapOptimized(head);
+
+	return ret;
+}
+
+/**
+ * hugetlb_vmemmap_optimize - optimize @head page's vmemmap pages.
+ * @h:		struct hstate.
+ * @head:	the head page whose vmemmap pages will be optimized.
+ *
+ * This function only tries to optimize @head's vmemmap pages and does not
+ * guarantee that the optimization will succeed after it returns. The caller
+ * can use HPageVmemmapOptimized(@head) to detect if @head's vmemmap pages
+ * have been optimized.
+ */
+void hugetlb_vmemmap_optimize(const struct hstate *h, struct page *head)
+{
+	LIST_HEAD(vmemmap_pages);
+
+	__hugetlb_vmemmap_optimize(h, head, &vmemmap_pages);
+	free_vmemmap_page_list(&vmemmap_pages);
 }
 
 void hugetlb_vmemmap_optimize_folios(struct hstate *h, struct list_head *folio_list)
 {
 	struct folio *folio;
+	LIST_HEAD(vmemmap_pages);
 
-	list_for_each_entry(folio, folio_list, lru)
-		hugetlb_vmemmap_optimize(h, &folio->page);
+	list_for_each_entry(folio, folio_list, lru) {
+		int ret = __hugetlb_vmemmap_optimize(h, &folio->page,
+								&vmemmap_pages);
+
+		/*
+		 * Pages may have been accumulated, thus free what we have
+		 * and try again.
+		 */
+		if (ret == -ENOMEM) {
+			free_vmemmap_page_list(&vmemmap_pages);
+			INIT_LIST_HEAD(&vmemmap_pages);
+			__hugetlb_vmemmap_optimize(h, &folio->page, &vmemmap_pages);
+		}
+	}
+
+	free_vmemmap_page_list(&vmemmap_pages);
 }
 
 static struct ctl_table hugetlb_vmemmap_sysctls[] = {
_

Patches currently in -mm which might be from mike.kravetz@oracle.com are

hugetlb-set-hugetlb-page-flag-before-optimizing-vmemmap.patch
hugetlb-optimize-update_and_free_pages_bulk-to-avoid-lock-cycles.patch
hugetlb-restructure-pool-allocations.patch
hugetlb-perform-vmemmap-optimization-on-a-list-of-pages.patch
hugetlb-perform-vmemmap-restoration-on-a-list-of-pages.patch
hugetlb-batch-freeing-of-vmemmap-pages.patch
hugetlb-batch-tlb-flushes-when-restoring-vmemmap.patch