linux-kernel - Re: [PATCH] fs: use kmalloc() to allocate fdmem if possible

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Message-ID: <4BDE9753.1080106@redhat.com>
Date:	Mon, 03 May 2010 12:28:51 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Jiri Slaby <jslaby@...e.cz>
CC:	Changli Gao <xiaosuo@...il.com>,
	Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
	akpm@...ux-foundation.org, paulmck@...ux.vnet.ibm.com,
	adobriyan@...il.com, mingo@...e.hu, peterz@...radead.org,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] fs: use kmalloc() to allocate fdmem if possible

On 05/03/2010 12:22 PM, Jiri Slaby wrote:
> On 05/03/2010 11:18 AM, Avi Kivity wrote:
>    
>> On 05/03/2010 12:03 PM, Jiri Slaby wrote:
>>      
>>>>> Because vmalloc is used to allocate virtually contiguous memory. v in
>>>>> vmalloc means virtually.
>>>>>
>>>>>
>>>>>
>>>>>            
>>>> A kmalloc()ed page is virtually contiguous, satisfying your requirement.
>>>>
>>>>          
>>> But it won't work well for vmalloc_to_{page,pfn} and similar.
>>>        
>> Modify vmalloc_to_{page,pfn} accordingly.
>>      
> When you get a slub in the middle of page, how?
>    

Er, right.  So a separate API is needed for users who are interested in 
memory, not pages.

>>> Some code
>>> may expect vmalloc result to be in the vmalloc area and page-aligned
>>> (both in position and size).
>>>
>>>        
>> Both would be a bug IMO.  vmalloc() follows kmalloc() and malloc() which
>> only guarantee natural alignment.
>>      
> Nope, from what I understand, vmalloc aligns (uses page allocator). Even
> for purposes of vmalloc_to_*.
>    

Correct, my mistake.

-- 
error compiling committee.c: too many arguments to function

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