From: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
In some cases cache avoiding clearing huge page may slow down workload.
Let's provide an sysctl handle to disable it.
We use static_key here to avoid extra work on fast path.
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
---
Documentation/sysctl/vm.txt | 13 ++++++++++++
include/linux/mm.h | 5 ++++
kernel/sysctl.c | 12 +++++++++++
mm/memory.c | 44 +++++++++++++++++++++++++++++++++++++-----
4 files changed, 68 insertions(+), 6 deletions(-)
diff --git a/Documentation/sysctl/vm.txt b/Documentation/sysctl/vm.txt
index 078701f..9559a97 100644
--- a/Documentation/sysctl/vm.txt
+++ b/Documentation/sysctl/vm.txt
@@ -19,6 +19,7 @@ files can be found in mm/swap.c.
Currently, these files are in /proc/sys/vm:
- block_dump
+- clear_huge_page_nocache
- compact_memory
- dirty_background_bytes
- dirty_background_ratio
@@ -74,6 +75,18 @@ huge pages although processes will also directly compact memory as required.
==============================================================
+clear_huge_page_nocache
+
+Available only when the architecture provides ARCH_HAS_USER_NOCACHE and
+CONFIG_TRANSPARENT_HUGEPAGE or CONFIG_HUGETLBFS is set.
+
+When set to 1 (default) kernel will use cache avoiding clear routine for
+clearing huge pages. This minimize cache pollution.
+When set to 0 kernel will clear huge pages through cache. This may speed
+up some workloads. Also it's useful for benchmarking propose.
+
+==============================================================
+
dirty_background_bytes
Contains the amount of dirty memory at which the background kernel
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 2858723..9b48f43 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1643,6 +1643,11 @@ extern void clear_huge_page(struct page *page,
extern void copy_user_huge_page(struct page *dst, struct page *src,
unsigned long addr, struct vm_area_struct *vma,
unsigned int pages_per_huge_page);
+#ifdef ARCH_HAS_USER_NOCACHE
+extern int sysctl_clear_huge_page_nocache;
+extern int clear_huge_page_nocache_handler(struct ctl_table *table, int write,
+ void __user *buffer, size_t *length, loff_t *ppos);
+#endif
#endif /* CONFIG_TRANSPARENT_HUGEPAGE || CONFIG_HUGETLBFS */
#ifdef CONFIG_DEBUG_PAGEALLOC
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 87174ef..80ccc67 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -1366,6 +1366,18 @@ static struct ctl_table vm_table[] = {
.extra2 = &one,
},
#endif
+#if defined(ARCH_HAS_USER_NOCACHE) && \
+ (defined(CONFIG_TRANSPARENT_HUGEPAGE) || defined(CONFIG_HUGETLBFS))
+ {
+ .procname = "clear_huge_page_nocache",
+ .data = &sysctl_clear_huge_page_nocache,
+ .maxlen = sizeof(sysctl_clear_huge_page_nocache),
+ .mode = 0644,
+ .proc_handler = clear_huge_page_nocache_handler,
+ .extra1 = &zero,
+ .extra2 = &one,
+ },
+#endif
{ }
};
diff --git a/mm/memory.c b/mm/memory.c
index 625ca33..395d574 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -57,6 +57,7 @@
#include <linux/swapops.h>
#include <linux/elf.h>
#include <linux/gfp.h>
+#include <linux/static_key.h>
#include <asm/io.h>
#include <asm/pgalloc.h>
@@ -3970,12 +3971,43 @@ EXPORT_SYMBOL(might_fault);
#if defined(CONFIG_TRANSPARENT_HUGEPAGE) || defined(CONFIG_HUGETLBFS)
-#ifndef ARCH_HAS_USER_NOCACHE
-#define ARCH_HAS_USER_NOCACHE 0
-#endif
+#ifdef ARCH_HAS_USER_NOCACHE
+int sysctl_clear_huge_page_nocache = 1;
+static DEFINE_MUTEX(sysctl_clear_huge_page_nocache_lock);
+static struct static_key clear_huge_page_nocache __read_mostly =
+ STATIC_KEY_INIT_TRUE;
-#if ARCH_HAS_USER_NOCACHE == 0
+static inline int is_nocache_enabled(void)
+{
+ return static_key_true(&clear_huge_page_nocache);
+}
+
+int clear_huge_page_nocache_handler(struct ctl_table *table, int write,
+ void __user *buffer, size_t *length, loff_t *ppos)
+{
+ int orig_value = sysctl_clear_huge_page_nocache;
+ int ret;
+
+ mutex_lock(&sysctl_clear_huge_page_nocache_lock);
+ orig_value = sysctl_clear_huge_page_nocache;
+ ret = proc_dointvec_minmax(table, write, buffer, length, ppos);
+ if (!ret && write && sysctl_clear_huge_page_nocache != orig_value) {
+ if (sysctl_clear_huge_page_nocache)
+ static_key_slow_inc(&clear_huge_page_nocache);
+ else
+ static_key_slow_dec(&clear_huge_page_nocache);
+ }
+ mutex_unlock(&sysctl_clear_huge_page_nocache_lock);
+
+ return ret;
+}
+#else
#define clear_user_highpage_nocache clear_user_highpage
+
+static inline int is_nocache_enabled(void)
+{
+ return 0;
+}
#endif
static void clear_gigantic_page(struct page *page,
@@ -3991,7 +4023,7 @@ static void clear_gigantic_page(struct page *page,
for (i = 0, vaddr = haddr; i < pages_per_huge_page;
i++, p = mem_map_next(p, page, i), vaddr += PAGE_SIZE) {
cond_resched();
- if (!ARCH_HAS_USER_NOCACHE || i == target)
+ if (!is_nocache_enabled() || i == target)
clear_user_highpage(p, vaddr);
else
clear_user_highpage_nocache(p, vaddr);
@@ -4015,7 +4047,7 @@ void clear_huge_page(struct page *page,
for (i = 0, vaddr = haddr; i < pages_per_huge_page;
i++, page++, vaddr += PAGE_SIZE) {
cond_resched();
- if (!ARCH_HAS_USER_NOCACHE || i == target)
+ if (!is_nocache_enabled() || i == target)
clear_user_highpage(page, vaddr);
else
clear_user_highpage_nocache(page, vaddr);
--
1.7.7.6
--
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