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/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: Zhang Qilong <zhangqilong3@huawei.com>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Tested-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Acked-by: David 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: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Zhang Qilong 2025-07-31 20:23:05 +08:00 committed by Andrew Morton
parent 337135e612
commit 849d5cff4d
1 changed files with 17 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

21
drivers/char/mem.c
View File

@ -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)