Commit 849d5cff authored by Zhang Qilong's avatar Zhang Qilong Committed by Andrew Morton
Browse files

/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.

Link: https://lkml.kernel.org/r/20250731122305.2669090-1-zhangqilong3@huawei.com


Signed-off-by: default avatarZhang Qilong <zhangqilong3@huawei.com>
Reviewed-by: default avatarLorenzo Stoakes <lorenzo.stoakes@oracle.com>
Tested-by: default avatarLorenzo Stoakes <lorenzo.stoakes@oracle.com>
Acked-by: default avatarDavid Hildenbrand <david@redhat.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Nanyong Sun <sunnanyong@huawei.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 337135e6

drivers/char/mem.c

+17 −4
Original line number Diff line number Diff line
@@ -512,11 +512,18 @@ static int mmap_zero(struct file *file, struct vm_area_struct *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,
@@ -527,12 +534,18 @@ static unsigned long get_unmapped_area_zero(struct file *file, 
		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)