linux-kernel - Re: [PATCH] reduce stack usage of node_read

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Date:	Fri,  9 Jul 2010 09:14:31 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	kosaki.motohiro@...fujitsu.com,
	LKML <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>
Subject: Re: [PATCH] reduce stack usage of node_read_meminfo()

> On Thu,  8 Jul 2010 18:20:14 +0900 (JST)
> KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com> wrote:
> 
> > 
> > Now, cmpilation node_read_meminfo() output following warning. Because
> > it has very large sprintf() argument.
> > 
> > 	drivers/base/node.c: In function 'node_read_meminfo':
> > 	drivers/base/node.c:139: warning: the frame size of 848 bytes is
> > 	larger than 512 bytes
> 
> hm, I'm surprised it's that much.

me too.

> 
> > --- a/drivers/base/node.c
> > +++ b/drivers/base/node.c
> > @@ -66,8 +66,7 @@ static ssize_t node_read_meminfo(struct sys_device * dev,
> >  	struct sysinfo i;
> >  
> >  	si_meminfo_node(&i, nid);
> > -
> > -	n = sprintf(buf, "\n"
> > +	n = sprintf(buf,
> >  		       "Node %d MemTotal:       %8lu kB\n"
> >  		       "Node %d MemFree:        %8lu kB\n"
> >  		       "Node %d MemUsed:        %8lu kB\n"
> > @@ -78,13 +77,33 @@ static ssize_t node_read_meminfo(struct sys_device * dev,
> >  		       "Node %d Active(file):   %8lu kB\n"
> >  		       "Node %d Inactive(file): %8lu kB\n"
> >  		       "Node %d Unevictable:    %8lu kB\n"
> > -		       "Node %d Mlocked:        %8lu kB\n"
> > +		       "Node %d Mlocked:        %8lu kB\n",
> > +		       nid, K(i.totalram),
> > +		       nid, K(i.freeram),
> > +		       nid, K(i.totalram - i.freeram),
> > +		       nid, K(node_page_state(nid, NR_ACTIVE_ANON) +
> > +				node_page_state(nid, NR_ACTIVE_FILE)),
> 
> Why the heck did we decide to print the same node-id 10000 times?

dunno. but I don't want to make behavior change for only stack reducing.


> 
> > +	n += sprintf(buf,
> 
> You just got caught sending untested patches.
> 
> --- a/drivers/base/node.c~drivers-base-nodec-reduce-stack-usage-of-node_read_meminfo-fix
> +++ a/drivers/base/node.c
> @@ -93,7 +93,7 @@ static ssize_t node_read_meminfo(struct 
>  		       nid, K(node_page_state(nid, NR_MLOCK)));
>  
>  #ifdef CONFIG_HIGHMEM
> -	n += sprintf(buf,
> +	n += sprintf(buf + n,
>  		       "Node %d HighTotal:      %8lu kB\n"
>  		       "Node %d HighFree:       %8lu kB\n"
>  		       "Node %d LowTotal:       %8lu kB\n"
> @@ -103,7 +103,7 @@ static ssize_t node_read_meminfo(struct 
>  		       nid, K(i.totalram - i.totalhigh),
>  		       nid, K(i.freeram - i.freehigh));
>  #endif
> -	n += sprintf(buf,
> +	n += sprintf(buf + n,
>  		       "Node %d Dirty:          %8lu kB\n"
>  		       "Node %d Writeback:      %8lu kB\n"
>  		       "Node %d FilePages:      %8lu kB\n"
> _
> 
> 
> Please, run the code and check that we didn't muck up the output.

100% my fault. I ran it, but I forgot to merge two patches ;)




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