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Message-ID: <20250731122305.2669090-1-zhangqilong3@huawei.com>
Date: Thu, 31 Jul 2025 20:23:05 +0800
From: Zhang Qilong <zhangqilong3@...wei.com>
To: <arnd@...db.de>, <gregkh@...uxfoundation.org>, <akpm@...ux-foundation.org>
CC: <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
<lorenzo.stoakes@...cle.com>, <wangkefeng.wang@...wei.com>,
<sunnanyong@...wei.com>, Zhang Qilong <zhangqilong3@...wei.com>, David
Hildenbrand <david@...hat.com>
Subject: [PATCH v4] /dev/zero: try to align PMD_SIZE for private mapping
Attempt to map aligned to huge page size for private mapping which
could achieve performance gains, the mprot_tw4m in libMicro average
execution time on arm64:
- Test case: mprot_tw4m
- Before the patch: 22 us
- After the patch: 17 us
If THP config is not set, we fall back to system page size mappings.
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Tested-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Acked-by: David Hildenbrand <david@...hat.com>
Signed-off-by: Zhang Qilong <zhangqilong3@...wei.com>
---
v4:
- collect Tested-by and Reviewed-by
- add comment for CONFIG_MMU #endif
v3:
- collect Acked-by
- factor out the #ifdef CONFIG_MMU in get_unmapped_area_zero(), per Lorenzo
- explicitly use #ifdef CONFIG_TRANSPARENT_HUGEPAGE, per Lorenzo and Matthew
v2:
- add comments on code suggested by Lorenzo
- use IS_ENABLED to check THP config
drivers/char/mem.c | 21 +++++++++++++++++----
1 file changed, 17 insertions(+), 4 deletions(-)
diff --git a/drivers/char/mem.c b/drivers/char/mem.c
index 48839958b0b1..34b815901b20 100644
--- a/drivers/char/mem.c
+++ b/drivers/char/mem.c
@@ -510,31 +510,44 @@ static int mmap_zero(struct file *file, struct vm_area_struct *vma)
return shmem_zero_setup(vma);
vma_set_anonymous(vma);
return 0;
}
+#ifndef CONFIG_MMU
+static unsigned long get_unmapped_area_zero(struct file *file,
+ unsigned long addr, unsigned long len,
+ unsigned long pgoff, unsigned long flags)
+{
+ return -ENOSYS;
+}
+#else
static unsigned long get_unmapped_area_zero(struct file *file,
unsigned long addr, unsigned long len,
unsigned long pgoff, unsigned long flags)
{
-#ifdef CONFIG_MMU
if (flags & MAP_SHARED) {
/*
* mmap_zero() will call shmem_zero_setup() to create a file,
* so use shmem's get_unmapped_area in case it can be huge;
* and pass NULL for file as in mmap.c's get_unmapped_area(),
* so as not to confuse shmem with our handle on "/dev/zero".
*/
return shmem_get_unmapped_area(NULL, addr, len, pgoff, flags);
}
- /* Otherwise flags & MAP_PRIVATE: with no shmem object beneath it */
- return mm_get_unmapped_area(current->mm, file, addr, len, pgoff, flags);
+ /*
+ * Otherwise flags & MAP_PRIVATE: with no shmem object beneath it,
+ * attempt to map aligned to huge page size if possible, otherwise we
+ * fall back to system page size mappings.
+ */
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+ return thp_get_unmapped_area(file, addr, len, pgoff, flags);
#else
- return -ENOSYS;
+ return mm_get_unmapped_area(current->mm, file, addr, len, pgoff, flags);
#endif
}
+#endif /* CONFIG_MMU */
static ssize_t write_full(struct file *file, const char __user *buf,
size_t count, loff_t *ppos)
{
return -ENOSPC;
--
2.43.0
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