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

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Date:	Tue, 11 Nov 2008 23:06:26 +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

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.

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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