linux-kernel - Re: [PATCH] staging: exfat: add exfat filesystem code to staging

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Date:   Fri, 30 Aug 2019 20:04:20 +0800
From:   Gao Xiang <hsiangkao@....com>
To:     Dan Carpenter <dan.carpenter@...cle.com>
Cc:     Gao Xiang <gaoxiang25@...wei.com>, devel@...verdev.osuosl.org,
        Christoph Hellwig <hch@...radead.org>,
        Valdis Klētnieks <valdis.kletnieks@...edu>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org,
        Sasha Levin <alexander.levin@...rosoft.com>,
        linux-fsdevel@...r.kernel.org,
        OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
Subject: Re: [PATCH] staging: exfat: add exfat filesystem code to staging

Hi Dan,

On Fri, Aug 30, 2019 at 02:26:12PM +0300, Dan Carpenter wrote:
> On Fri, Aug 30, 2019 at 04:43:33PM +0800, Gao Xiang wrote:
> > Hi Dan,
> > 
> > On Fri, Aug 30, 2019 at 11:34:45AM +0300, Dan Carpenter wrote:
> > > On Fri, Aug 30, 2019 at 12:04:41AM +0800, Gao Xiang wrote:
> > > > Anyway, I'm fine to delete them all if you like, but I think majority of these
> > > > are meaningful.
> > > > 
> > > > data.c-		/* page is already locked */
> > > > data.c-		DBG_BUGON(PageUptodate(page));
> > > > data.c-
> > > > data.c:		if (unlikely(err))
> > > > data.c-			SetPageError(page);
> > > > data.c-		else
> > > > data.c-			SetPageUptodate(page);
> > > 
> > > If we cared about speed here then we would delete the DBG_BUGON() check
> > > because that's going to be expensive.  The likely/unlikely annotations
> > > should be used in places a reasonable person thinks it will make a
> > > difference to benchmarks.
> > 
> > DBG_BUGON will be a no-op ((void)x) in non-debugging mode,
> 
> It expands to:
> 
> 	((void)PageUptodate(page));
> 
> Calling PageUptodate() doesn't do anything, but it isn't free.  The
> time it takes to do that function call completely negates any speed up
> from using likely/unlikely.
> 
> I'm really not trying to be a jerk...

You are right, I recalled that PageUptodate is not as simple as it implys.
Yes, those are all removed now... I am ok with that,
thanks for your suggestion :)

Thanks,
Gao Xiang

> 
> regards,
> dan carpenter
>