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

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Message-Id: <201301142338.AA04488@capsicum.lab.ntt.co.jp>
Date:	Tue, 15 Jan 2013 08:38:09 +0900
From:	Ryusuke Konishi <konishi.ryusuke@....ntt.co.jp>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	slava@...eyko.com, 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 Sun, 13 Jan 2013 16:07:23 +0900 (JST)
>Ryusuke Konishi <konishi.ryusuke@....ntt.co.jp> wrote:
>
>> 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.
>
>I added a Cc:stable so the fix will be backported into earlier kernels.
>40 minutes mount time is pretty bad!

Yup, I agree.

Thanks.

Ryusuke Konishi

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