Re: [PATCH 07/10] mbind: add hugepage migration code to mbind()

[KOSAKI Motohiro]

>> -	if (!new_hpage)
>> +	/*
>> +	 * Getting a new hugepage with alloc_huge_page() (which can happen
>> +	 * when migration is caused by mbind()) can return ERR_PTR value,
>> +	 * so we need take care of the case here.
>> +	 */
>> +	if (!new_hpage || IS_ERR_VALUE(new_hpage))
>>  		return -ENOMEM;
> 
> Please no. get_new_page returns NULL or a page. You are hooking a wrong
> callback here. The error value doesn't make any sense here. IMO you
> should just wrap alloc_huge_page by something that returns NULL or page.

I suggest just opposite way. new_vma_page() always return ENOMEM, ENOSPC etc instad 
of NULL. and caller propegate it to userland.
I guess userland want to distingush why mbind was failed.

Anyway, If new_vma_page() have a change to return both NULL and -ENOMEM. That's a bug.

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