linux-kernel - Re: [PATCH] xfs: reduce stack usage in xfs_bmap

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Date:	Sun, 27 Apr 2008 01:05:17 +0200
From:	Denys Vlasenko <vda.linux@...glemail.com>
To:	Eric Sandeen <sandeen@...deen.net>
Cc:	David Chinner <dgc@....com>, xfs@....sgi.com,
	Adrian Bunk <bunk@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] xfs: reduce stack usage in xfs_bmap_btalloc()

On Saturday 26 April 2008 20:54, Eric Sandeen wrote:
> > This patch reduces xfs_bmap_btalloc() stack usage by 50 bytes
> > by moving part of its body into a helper function.
> > 
> > This results in some variables not taking stack space in
> > xfs_bmap_btalloc() anymore.
> > 
> > The helper itself does not call anything stack-deep.
> > Stack-deep call to xfs_alloc_vextent() happen
> > in xfs_bmap_btalloc(), as before.
> > 
> > Compile tested only.
> > 
> > Signed-off-by: Denys Vlasenko <vda.linux@...glemail.com>
> 
> Looks like a very good approach, it pushes a lot of large local vars off
> into the helper.
> 
> There is one build-time problem if DEBUG is turned on:
> 
>         if (args.fsbno != NULLFSBLOCK) {
>                 ap->firstblock = ap->rval = args.fsbno;
>                 ASSERT(nullfb || fb_agno == args.agno ||
>                        (ap->low && fb_agno < args.agno));
> 
> in xfs_bmap_btalloc, which no longer has an fb_agno variable which the
> ASSERT macro uses.

Do you want me to rework and resend the patch?
--
vda
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