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Date: Tue, 15 Apr 2008 02:35:05 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Pavel Machek <pavel@ucw.cz>
Cc: kernel list <linux-kernel@vger.kernel.org>
Subject: Re: mm/page_alloc.c: remove hand-coded get_order()
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On Tue, 15 Apr 2008 11:23:27 +0200 Pavel Machek <pavel@ucw.cz> wrote:

> 
> __get_free_pages() is strange interface:
> 
> It has underscores, yet get_free_pages() does not exists.
> 
> It returns long when most people need pointer.

It is a bit odd.

> (And it takes order, when many people want to pass size).
> 
> What about creating void *get_free_pages(flags, order) version,

Sounds sensible.  It matches free_pages().

> then slowly converting users to it?

alas, poor me.

> 
> ---
> 
> Remove hand-coded get_order() from page_alloc.c.
> 
> Signed-off-by: Pavel Machek <pavel@suse.cz>
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 402a504..c48aa45 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -4339,9 +4339,7 @@ void *__init alloc_large_system_hash(con
>  		else if (hashdist)
>  			table = __vmalloc(size, GFP_ATOMIC, PAGE_KERNEL);
>  		else {
> -			unsigned long order;
> -			for (order = 0; ((1UL << order) << PAGE_SHIFT) < size; order++)
> -				;
> +			unsigned long order = get_order(size);
>  			table = (void*) __get_free_pages(GFP_ATOMIC, order);
>  			/*
>  			 * If bucketsize is not a power-of-two, we may free
> 

OK.  get_order() does round up, doesn't it?  We seem to have forgotten to
document that rather important detail.