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

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Message-ID: <515F4ECB.9050105@gmail.com>
Date:	Fri, 05 Apr 2013 18:23:07 -0400
From:	KOSAKI Motohiro <kosaki.motohiro@...il.com>
To:	Michal Hocko <mhocko@...e.cz>
CC:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>, linux-mm@...ck.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mel@....ul.ie>, Hugh Dickins <hughd@...gle.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Andi Kleen <andi@...stfloor.org>,
	Hillf Danton <dhillf@...il.com>, linux-kernel@...r.kernel.org,
	kosaki.motohiro@...il.com
Subject: Re: [PATCH 07/10] mbind: add hugepage migration code to mbind()

>> -	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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