linux-kernel - Re: [PATCH] Allocate module.ref array dynamically

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Date:	Tue, 11 Nov 2008 23:15:50 +0100
From:	Eric Dumazet <dada1@...mosbay.com>
To:	Takashi Iwai <tiwai@...e.de>
CC:	Rusty Russell <rusty@...tcorp.com.au>,
	Andreas Gruenbacher <agruen@...e.de>,
	Jan Blunck <jblunck@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Mike Travis <travis@....com>
Subject: Re: [PATCH] Allocate module.ref array dynamically

Eric Dumazet a écrit :
> Takashi Iwai a écrit :
>> Hi,
>>
>> we found that the kernel module sizes and memory footprints
>> grow drastically when NR_CPUS is high.  For example, with
>> NR_CPUS=4096, SUSE kernel packages weigh over 500MB (even w/o debug
>> info).
>>
>> A part of the reason is the fixed size array in struct module.
>> The patch below fixes the problem by allocating it dynamically.
>> With the patch, the size can go down to 20MB.
>>
>>
>> Any comments/suggestions appreciated.
>>
> 
> Many attempts were done on this area on the past.

Forgot to include a link to previous attempt : http://lkml.org/lkml/2008/5/15/402

> 
> Your patch has the drawback of using kcalloc(), while previously, 
> module_ref
> space was allocated with vmalloc().
> 
> After a while, a machine could have a lot of vmalloc() space available, 
> but not enough
> physically contiguous space to fullfill a kmalloc(large_area) call.
> 
> So a module load could fail, while previous code could load module.
> 
> I believe Mike Travis has a better patch for this problem, partly using 
> new percpu allocator.
> 


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