linux-kernel - Re: [PATCH] nilfs2: fix very long mount time issue

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Message-Id: <20130113.160723.135185368.konishi.ryusuke@lab.ntt.co.jp>
Date:	Sun, 13 Jan 2013 16:07:23 +0900 (JST)
From:	Ryusuke Konishi <konishi.ryusuke@....ntt.co.jp>
To:	slava@...eyko.com, akpm@...ux-foundation.org
Cc:	splavgm@...il.com, linux-nilfs@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] nilfs2: fix very long mount time issue

On Sat, 12 Jan 2013 19:34:48 +0400, Vyacheslav Dubeyko wrote:
> From: Vyacheslav Dubeyko <slava@...eyko.com>
> Subject: [PATCH] nilfs2: fix very long mount time issue
> 
> DESCRIPTION:
> It exists situation when GC can work in background alone without any other filesystem activity during significant time. The nilfs_clean_segments() method calls nilfs_segctor_construct() that updates superblocks in the case of NILFS_SC_SUPER_ROOT and THE_NILFS_DISCONTINUED flags are set. But when GC is working alone the nilfs_clean_segments() is called with unset THE_NILFS_DISCONTINUED flag. As a result, the update of superblocks doesn't occurred all this time and in the case of SPOR superblocks keep very old values of last super root placement.
> 
> SYMPTOMS:
> Trying to mount a NILFS2 volume after SPOR in such environment ends with very long mounting time (it can achieve about several hours in some cases).
> 
> REPRODUCING PATH:
> 1. It needs to use external USB HDD, disable automount and doesn't make any additional filesystem activity on the NILFS2 volume.
> 2. Generate temporary file with size about 100 - 500 GB (for example, dd if=/dev/zero of=<file_name> bs=1073741824 count=200). The size of file defines duration of GC working.
> 3. Then it needs to delete file.
> 4. Start GC manually by means of command "nilfs-clean -p 0". When you start GC by means of such way then, at the end, superblocks is updated by once. So, for simulation of SPOR, it needs to wait sometime (15 - 40 minutes) and simply switch off USB HDD manually.
> 5. Switch on USB HDD again and try to mount NILFS2 volume. As a result, NILFS2 volume will mount during very long time.
> 
> REPRODUCIBILITY: 100%
> 
> FIX:
> This patch adds checking that superblocks need to update and set THE_NILFS_DISCONTINUED flag before nilfs_clean_segments() call.
> 
> Reported-by: Sergey Alexandrov <splavgm@...il.com>
> Signed-off-by: Vyacheslav Dubeyko <slava@...eyko.com>
> Tested-by: Vyacheslav Dubeyko <slava@...eyko.com>

Acked-by: Ryusuke Konishi <konishi.ryusuke@....ntt.co.jp>

Thanks, Vyacheslav.  I confirmed the issue and could reproduce it.
Your patch fixed it.

Andrew, please apply.

Thanks,
Ryusuke Konishi

> ---
>  fs/nilfs2/ioctl.c |    5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/nilfs2/ioctl.c b/fs/nilfs2/ioctl.c
> index fdb1807..f385935 100644
> --- a/fs/nilfs2/ioctl.c
> +++ b/fs/nilfs2/ioctl.c
> @@ -664,8 +664,11 @@ static int nilfs_ioctl_clean_segments(struct inode *inode, struct file *filp,
>  	if (ret < 0)
>  		printk(KERN_ERR "NILFS: GC failed during preparation: "
>  			"cannot read source blocks: err=%d\n", ret);
> -	else
> +	else {
> +		if (nilfs_sb_need_update(nilfs))
> +			set_nilfs_discontinued(nilfs);
>  		ret = nilfs_clean_segments(inode->i_sb, argv, kbufs);
> +	}
>  
>  	nilfs_remove_all_gcinodes(nilfs);
>  	clear_nilfs_gc_running(nilfs);
> -- 
> 1.7.9.5
> 
> 
> 
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