linux-kernel - Re: [PATCH 2/6] change alloc function in pcpu_alloc

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Date:	Thu, 15 Apr 2010 19:21:22 +0900
From:	Minchan Kim <minchan.kim@...il.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	Mel Gorman <mel@....ul.ie>,
	Andrew Morton <akpm@...ux-foundation.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Bob Liu <lliubbo@...il.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, Christoph Lameter <cl@...ux-foundation.org>
Subject: Re: [PATCH 2/6] change alloc function in pcpu_alloc_pages

On Thu, Apr 15, 2010 at 7:08 PM, Tejun Heo <tj@...nel.org> wrote:
> Hello,
>
> On 04/15/2010 06:40 PM, Minchan Kim wrote:
>>> I'm not an expert on that part of the kernel but isn't
>>> alloc_pages_any_node() identical to alloc_pages_exact_node()?  All
>>
>> alloc_pages_any_node means user allows allocated pages in any
>> node(most likely current node) alloc_pages_exact_node means user
>> allows allocated pages in nid node if he doesn't use __GFP_THISNODE.
>
> Ooh, sorry, I meant alloc_pages().  What would be the difference
> between alloc_pages_any_node() and alloc_pages()?

It's no different. It's same. Just naming is more explicit. :)
I think it could be following as.

#define alloc_pages alloc_pages_any_node.
strucdt page * alloc_pages_node() {
   int nid = numa_node_id();
   ...
   return page;
}

>
>>> introducing new API just to weed out invalid usages seems like an
>>> overkill.
>>
>> It might be.
>>
>> It think it's almost same add_to_page_cache and add_to_page_cache_locked.
>> If user knows the page is already locked, he can use
>> add_to_page_cache_locked for performance gain and code readability
>> which we need to lock the page before calling it.
>
> Yeah, if both APIs are necessary at the end of the conversion, sure.
> I was just saying that introducing new APIs just to weed out invalid
> usages and then later killing the old API would be rather excessive.
>
> I was just wondering whether we could just clean up alloc_pages_node()
> users and kill alloc_pages_exact_node().

kill alloc_pages_exact_node?
Sorry but I can't understand your point.
I don't want to kill user of alloc_pages_exact_node.
That's opposite.
I want to kill user of alloc_pages_node and change it with
alloc_pages_any_node or alloc_pages_exact_node. :)

I think we can do it. That's because all of caller already can check nid == -1
before calling allocation function explicitly if he cares node locality.

-- 
Kind regards,
Minchan Kim
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