From mboxrd@z Thu Jan  1 00:00:00 1970
From: Andreas Dilger <adilger@sun.com>
Subject: Re: [RFC] quota: 64-bit limits with vfs
Date: Sat, 15 Mar 2008 12:23:16 +0800
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Cc: Jan Kara <jack@suse.cz>, linux-fsdevel@vger.kernel.org,
	Johann Lombardi <Johann.Lombardi@sun.com>,
	Zhiyong Landen tian <Zhiyong.Tian@sun.com>,
	Alex Lyashkov <Alexey.Lyashkov@sun.com>
To: Andrew Perepechko <Andrew.Perepechko@sun.com>
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On Mar 14, 2008  16:08 +0300, Andrew Perepechko wrote:
> @@ -395,7 +463,10 @@ static int v2_write_dquot(struct dquot *
>  {
>  	int type = dquot->dq_type;
>  	ssize_t ret;
> -	struct v2_disk_dqblk ddquot, empty;
> +	union v2_disk_dqblk ddquot, empty;
> +	struct super_block *sb = dquot->dq_sb;
> +	uint rev = sb_dqopt(sb)->info[type].u.v2_i.dqi_revision;
> +	uint dqblksz = v2_dqblksz(rev);

In a few places you add new on-stack variables like "sb", but they aren't
used more than 1 or 2 times.  While it makes the code a tiny bit clearer
(though not largely so for "sb" because it is only dquot->dq_sb) it does
increase the stack usage, and that is never a good idea.

> +		union v2_disk_dqblk fakedquot;
>  
> +		memset(&fakedquot, 0, dqblksz);
> +		for (i = 0; i < dqstrinblk; i++)
> +			if (!DQF_GET(ddquot+i, rev, dqb_id) &&
> +			    memcmp(&fakedquot, ddquot+i, dqblksz))

Hmm, allocating "fakedquot" on the stack just to compare it to zero
doesn't seem like a good use of space.  What about doing the memcmp()
against page_address(ZERO_PAGE(0))?  It might be nice to have a permanent
mapping of ZERO_PAGE(0) like void *zero_buffer that can be used for this.

Cheers, Andreas
--
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.