# Re: \[PATCH v4 2/3\] mm/mempolicy: add set\_mempolicy\_home\_node syscall

- From: Aneesh Kumar K.V \<hidden\>
- Date: 2021-11-10 15:56:16 
- List: linux-api
- Page: https://ratatoskr.run/linux-api/2021/11/6512338
- Thread: https://ratatoskr.run/linux-mm/2021/11/6511882/t.md

```text
On 11/10/21 20:48, Jonathan Corbet wrote:
> "Aneesh Kumar K.V" [ref] writes:
>
>> This syscall can be used to set a home node for the MPOL_BIND
>> and MPOL_PREFERRED_MANY memory policy. Users should use this
>> syscall after setting up a memory policy for the specified range
>> as shown below.
>
> So I noticed one little thing as I was looking at this...
>
> [...]
>
>> +SYSCALL_DEFINE4(set_mempolicy_home_node, unsigned long, start, unsigned long, len,
>> +		unsigned long, home_node, unsigned long, flags)
>> +{
>> +	struct mm_struct *mm = current->mm;
>> +	struct vm_area_struct *vma;
>> +	struct mempolicy *new;
>> +	unsigned long vmstart;
>> +	unsigned long vmend;
>> +	unsigned long end;
>> +	int err = -ENOENT;
>> +
>> +	if (start & ~PAGE_MASK)
>> +		return -EINVAL;
>> +
>> +	len = (len + PAGE_SIZE - 1) & PAGE_MASK;
>> +	end = start + len;
>> +
>> +	if (end < start)
>> +		return -EINVAL;
>> +	if (end == start)
>> +		return 0;
>> +	mmap_write_lock(mm);
>> +	vma = find_vma(mm, start);
>> +	for (; vma && vma->vm_start < end;  vma = vma->vm_next) {
>> +
>> +		vmstart = max(start, vma->vm_start);
>> +		vmend   = min(end, vma->vm_end);
>> +		new = mpol_dup(vma_policy(vma));
>> +		if (IS_ERR(new)) {
>> +			err = PTR_ERR(new);
>> +			break;
>> +		}
>> +		/*
>> +		 * Only update home node if there is an existing vma policy
>> +		 */
>> +		if (!new)
>> +			continue;
>> +		new->home_node = home_node;
>> +		err = mbind_range(mm, vmstart, vmend, new);
>> +		if (err)
>> +			break;
>> +	}
>> +	mmap_write_unlock(mm);
>> +	return err;
>> +}
>
> You never do anything with flags; I believe you want to check and ensure
> that it's zero if there are no defined flags at this point?
>
>

Will update that in v5. I guess EINVAL is the right error for flags != 0?

-aneesh
```