linux-kernel - Re: [PATCH 2/2] f2fs: don't discard next free dnode page for an umount checkpoint

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Date:	Mon, 2 Feb 2015 15:37:34 -0800
From:	Jaegeuk Kim <jaegeuk@...nel.org>
To:	Chao Yu <chao2.yu@...sung.com>
Cc:	Changman Lee <cm224.lee@...sung.com>,
	linux-f2fs-devel@...ts.sourceforge.net,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] f2fs: don't discard next free dnode page for an
 umount checkpoint

Hi Chao,

On Sat, Jan 31, 2015 at 05:06:59PM +0800, Chao Yu wrote:
> Previously, discard_next_dnode is added before a checkpoint to prevent that we
> may meet a garbage dnode page readed from next free blkaddr in recover flow.
> 
> Since f2fs will skip recovery flow for a clean umount image, this condition will
> never happen.
> 
> So it's safe for us to leave next free dnode as it is in an umount checkpoint.
> 
> Signed-off-by: Chao Yu <chao2.yu@...sung.com>
> ---
>  fs/f2fs/checkpoint.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
> index f7cdcad..991fd0a 100644
> --- a/fs/f2fs/checkpoint.c
> +++ b/fs/f2fs/checkpoint.c
> @@ -905,8 +905,12 @@ static void do_checkpoint(struct f2fs_sb_info *sbi, struct cp_control *cpc)
>  	/*
>  	 * This avoids to conduct wrong roll-forward operations and uses
>  	 * metapages, so should be called prior to sync_meta_pages below.
> +	 * But if we are in an umount checkpoint, we'd better skip this
> +	 * because we will not enter recovery flow to use the next free
> +	 * blkaddr when mounting it.
>  	 */
> -	discard_next_dnode(sbi, NEXT_FREE_BLKADDR(sbi, curseg));
> +	if (cpc->reason != CP_UMOUNT)
> +		discard_next_dnode(sbi, NEXT_FREE_BLKADDR(sbi, curseg));

The reason for discard_next_dnode is to avoid wrong execution due to old
mkfs.f2fs which remains gabage data.
It needs to do all the time.

Thanks,

>  
>  	/* Flush all the NAT/SIT pages */
>  	while (get_pages(sbi, F2FS_DIRTY_META)) {
> -- 
> 2.2.1
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