To: Yum Rayan <yum.rayan@gmail.com>
Cc: linux-kernel@vger.kernel.org, mvw@planets.elm.net
Subject: Re: [PATCH] Reduce stack usage in acct.c
References: <df35dfeb05033023394170d6cc@mail.gmail.com>
From: Olaf Dietsche <olaf+list.linux-kernel@olafdietsche.de>
Date: Sun, 03 Apr 2005 13:35:19 +0200
In-Reply-To: <df35dfeb05033023394170d6cc@mail.gmail.com> (Yum Rayan's
 message of "Wed, 30 Mar 2005 23:39:40 -0800")
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Yum Rayan <yum.rayan@gmail.com> writes:

> Attempt to reduce stack usage in acct.c (linux-2.6.12-rc1-mm3). Stack
> usage was noted using checkstack.pl. Specifically:
>
> Before patch
> ------------
> check_free_space - 128
>
> After patch
> -----------
> check_free_space - 36
>
> Signed-off-by: Yum Rayan <yum.rayan@gmail.com>
>
> --- a/kernel/acct.c	2005-03-25 22:11:06.000000000 -0800
> +++ b/kernel/acct.c	2005-03-30 15:33:05.000000000 -0800
> @@ -103,30 +103,32 @@
>   */
>  static int check_free_space(struct file *file)
>  {
> -	struct kstatfs sbuf;
> -	int res;
> -	int act;
> -	sector_t resume;
> -	sector_t suspend;
> +	struct kstatfs *sbuf = NULL;
> +	int res, act;
> +	sector_t resume, suspend;

I can't see how you expect to save 128-36=92 bytes here. You replace
sizeof(struct kstatfs)=64 with sizeof(struct kstatfs*)=4, which would
be a saving of 60 bytes. But the call to kmalloc()/kfree() reduces
your stack saving further, not to mention the runtime penalty,
introduced by allocating dynamic memory.

Regards, Olaf.
-
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