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

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Message-ID: <4BDE95F2.1020506@suse.cz>
Date:	Mon, 03 May 2010 11:22:58 +0200
From:	Jiri Slaby <jslaby@...e.cz>
To:	Avi Kivity <avi@...hat.com>
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 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?

>> 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_*.

regards,
-- 
js
suse labs
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