linux-kernel - [PATCH 2/6] mm: hugetlb_vmemmap: optimize vmemmap_optimize

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Message-Id: <20220613063512.17540-3-songmuchun@bytedance.com>
Date:   Mon, 13 Jun 2022 14:35:08 +0800
From:   Muchun Song <songmuchun@...edance.com>
To:     mike.kravetz@...cle.com, david@...hat.com,
        akpm@...ux-foundation.org, corbet@....net
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, Muchun Song <songmuchun@...edance.com>
Subject: [PATCH 2/6] mm: hugetlb_vmemmap: optimize vmemmap_optimize_mode handling

We hold an another reference to hugetlb_optimize_vmemmap_key when
making vmemmap_optimize_mode on, because we use static_key to tell
memory_hotplug that memory_hotplug.memmap_on_memory should be
overridden.  However, this rule has gone when we have introduced
SECTION_CANNOT_OPTIMIZE_VMEMMAP.  Therefore, we could simplify
vmemmap_optimize_mode handling by not holding an another reference
to hugetlb_optimize_vmemmap_key.

Signed-off-by: Muchun Song <songmuchun@...edance.com>
---
 include/linux/page-flags.h |  6 ++---
 mm/hugetlb_vmemmap.c       | 65 +++++-----------------------------------------
 2 files changed, 9 insertions(+), 62 deletions(-)

diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index b8b992cb201c..da7ccc3b16ad 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -200,8 +200,7 @@ enum pageflags {
 #ifndef __GENERATING_BOUNDS_H
 
 #ifdef CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP
-DECLARE_STATIC_KEY_MAYBE(CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON,
-			 hugetlb_optimize_vmemmap_key);
+DECLARE_STATIC_KEY_FALSE(hugetlb_optimize_vmemmap_key);
 
 /*
  * If the feature of optimizing vmemmap pages associated with each HugeTLB
@@ -221,8 +220,7 @@ DECLARE_STATIC_KEY_MAYBE(CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON,
  */
 static __always_inline const struct page *page_fixed_fake_head(const struct page *page)
 {
-	if (!static_branch_maybe(CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON,
-				 &hugetlb_optimize_vmemmap_key))
+	if (!static_branch_unlikely(&hugetlb_optimize_vmemmap_key))
 		return page;
 
 	/*
diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
index e20a7082f2f8..132dc83f0130 100644
--- a/mm/hugetlb_vmemmap.c
+++ b/mm/hugetlb_vmemmap.c
@@ -23,42 +23,15 @@
 #define RESERVE_VMEMMAP_NR		1U
 #define RESERVE_VMEMMAP_SIZE		(RESERVE_VMEMMAP_NR << PAGE_SHIFT)
 
-enum vmemmap_optimize_mode {
-	VMEMMAP_OPTIMIZE_OFF,
-	VMEMMAP_OPTIMIZE_ON,
-};
-
-DEFINE_STATIC_KEY_MAYBE(CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON,
-			hugetlb_optimize_vmemmap_key);
+DEFINE_STATIC_KEY_FALSE(hugetlb_optimize_vmemmap_key);
 EXPORT_SYMBOL(hugetlb_optimize_vmemmap_key);
 
-static enum vmemmap_optimize_mode vmemmap_optimize_mode =
+static bool vmemmap_optimize_enabled =
 	IS_ENABLED(CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON);
 
-static void vmemmap_optimize_mode_switch(enum vmemmap_optimize_mode to)
-{
-	if (vmemmap_optimize_mode == to)
-		return;
-
-	if (to == VMEMMAP_OPTIMIZE_OFF)
-		static_branch_dec(&hugetlb_optimize_vmemmap_key);
-	else
-		static_branch_inc(&hugetlb_optimize_vmemmap_key);
-	WRITE_ONCE(vmemmap_optimize_mode, to);
-}
-
 static int __init hugetlb_vmemmap_early_param(char *buf)
 {
-	bool enable;
-	enum vmemmap_optimize_mode mode;
-
-	if (kstrtobool(buf, &enable))
-		return -EINVAL;
-
-	mode = enable ? VMEMMAP_OPTIMIZE_ON : VMEMMAP_OPTIMIZE_OFF;
-	vmemmap_optimize_mode_switch(mode);
-
-	return 0;
+	return kstrtobool(buf, &vmemmap_optimize_enabled);
 }
 early_param("hugetlb_free_vmemmap", hugetlb_vmemmap_early_param);
 
@@ -103,7 +76,7 @@ static unsigned int optimizable_vmemmap_pages(struct hstate *h,
 	unsigned long pfn = page_to_pfn(head);
 	unsigned long end = pfn + pages_per_huge_page(h);
 
-	if (READ_ONCE(vmemmap_optimize_mode) == VMEMMAP_OPTIMIZE_OFF)
+	if (!READ_ONCE(vmemmap_optimize_enabled))
 		return 0;
 
 	for (; pfn < end; pfn += PAGES_PER_SECTION) {
@@ -155,7 +128,6 @@ void __init hugetlb_vmemmap_init(struct hstate *h)
 
 	if (!is_power_of_2(sizeof(struct page))) {
 		pr_warn_once("cannot optimize vmemmap pages because \"struct page\" crosses page boundaries\n");
-		static_branch_disable(&hugetlb_optimize_vmemmap_key);
 		return;
 	}
 
@@ -176,36 +148,13 @@ void __init hugetlb_vmemmap_init(struct hstate *h)
 }
 
 #ifdef CONFIG_PROC_SYSCTL
-static int hugetlb_optimize_vmemmap_handler(struct ctl_table *table, int write,
-					    void *buffer, size_t *length,
-					    loff_t *ppos)
-{
-	int ret;
-	enum vmemmap_optimize_mode mode;
-	static DEFINE_MUTEX(sysctl_mutex);
-
-	if (write && !capable(CAP_SYS_ADMIN))
-		return -EPERM;
-
-	mutex_lock(&sysctl_mutex);
-	mode = vmemmap_optimize_mode;
-	table->data = &mode;
-	ret = proc_dointvec_minmax(table, write, buffer, length, ppos);
-	if (write && !ret)
-		vmemmap_optimize_mode_switch(mode);
-	mutex_unlock(&sysctl_mutex);
-
-	return ret;
-}
-
 static struct ctl_table hugetlb_vmemmap_sysctls[] = {
 	{
 		.procname	= "hugetlb_optimize_vmemmap",
-		.maxlen		= sizeof(enum vmemmap_optimize_mode),
+		.data		= &vmemmap_optimize_enabled,
+		.maxlen		= sizeof(int),
 		.mode		= 0644,
-		.proc_handler	= hugetlb_optimize_vmemmap_handler,
-		.extra1		= SYSCTL_ZERO,
-		.extra2		= SYSCTL_ONE,
+		.proc_handler	= proc_dobool,
 	},
 	{ }
 };
-- 
2.11.0