linux-kernel - Re: [PATCH] Reduce stack used by lib/hexdump.c

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Date:	Thu, 6 Dec 2007 00:58:38 -0500
From:	Kyle Moffett <mrmacman_g4@....com>
To:	Joe Perches <joe@...ches.com>
Cc:	Randy Dunlap <randy.dunlap@...cle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	jengelh@...putergmbh.de, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Reduce stack used by lib/hexdump.c

On Dec 05, 2007, at 21:42:35, Joe Perches wrote:
> On Wed, 2007-12-05 at 18:18 -0800, Randy Dunlap wrote:
>> Joe Perches wrote:
>>> Maybe just eliminate the 16 or 32 byte width option and force it  
>>> to only 16 byte widths.
>> Have you checked users (callers)?  I'm pretty sure that one of the  
>> callers wanted 32 and that's why it's there.
>
> I did.  There is only 1 subsystem.  That's easy to change.
>
> drivers/mtd/ubi/debug.c:  print_hex_dump(KERN_DEBUG, "",  
> DUMP_PREFIX_OFFSET, 32, 1,
> drivers/mtd/ubi/io.c:     print_hex_dump(KERN_DEBUG, "",  
> DUMP_PREFIX_OFFSET, 32, 1,
>
> Long lines in the log file are not too easy to read anyway.  Using  
> 16 byte dumps per line instead of 32 isn't painful.
>
> It gets rid of the allocation, reduces the argument count and makes  
> the kernel smaller.  I think it's all good.
>
> Every current caller would have to change though.

Alternatively, since print_hex_dump is not a performance-critical  
path (and usually indicates an error/debug condition), you could  
probably just make a static "hexdump_lock" spinlock and  
spin_lock_irqsave()/spin_unlock_irqrestore().  It would always nest  
inside any other lock (except during crash, where we break locks  
already for printk()), and I doubt any of the callers would notice  
the serialization since they're already serialized on the printk buffer.

Cheers,
Kyle Moffett

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