linux-ext4 - Re: [PATCH] ext4: Set file system to read-only by I/O error threshold

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Message-ID: <BANLkTim-1FfCZAm449zp5PpApbq027HGwYhoZBF0soZpJon9tQ@mail.gmail.com>
Date:	Mon, 20 Jun 2011 09:32:56 +0800
From:	Wang Shaoyan <stufever@...il.com>
To:	Lukas Czerner <lczerner@...hat.com>
Cc:	linux-ext4@...r.kernel.org,
	Wang Shaoyan <wangshaoyan.pt@...bao.com>,
	Ted Tso <tytso@....edu>, Jan Kara <jack@...e.cz>
Subject: Re: [PATCH] ext4: Set file system to read-only by I/O error threshold

2011/6/18 Lukas Czerner <lczerner@...hat.com>:

> Hi,
>
> so you're saying that you encounter I/O error on access(2) only with
> Ext3/4 with journal. So given that you're checking the error count in
> ext4_handle_error() which is called when I/O error happens I fail to see
> how this helps your case. Am I missing something ?
>
Only when access(2) return "Read-only file system", hadoop will mark
the disk as offline. For Ext4 no-journal mode, there is no jdb2 to set
the file system as
read-only when I/O error happens, so we set an threshold, when io
error number reach this number, we change the filesystem to read-only.
I use ext4_abort(), maybe it is wrong?
> Also I do not understand how this is helpful at all ? Usually when we
> hit I/O error we want to have predictable behavior set by the error=
> mount option, but with this patch we have absolutely unpredictable
> behaviour on errors, which is bad! Also we can end up with read-only
> file system even when errors=continue has been set.
>
In ext4 without journal, when the disk drops, the fs can't be
readonly. But in ext3/4 with journal, jbd2 will abort the filesystem,
change fs to be read-only. So we don't care what kind of error happen,
we just want to change fs to be read-only when there are too many
errors

> You can use atomic_t and get rid of the spinlock maybe ?
>
Yes, thanks

> The name for this function should rather be inc_sb_error_count().
Thanks

> I am not sure, but given that it it a "threshold" should not we trigger
> it when we hit the threshold and not threshold+1 ?
Thanks, I should use ">="

> Could you use better error message ? This does not say nothing about why
> it happened. Something about IO errors count reached the threshold ?
Yes,  IO errors count reached the threshold, we need change fs to be readonly

> Maybe you can use atomic operations and get rid of the spin_lock.
spin_lock is just a "lazy approach"

-- 
Wang Shaoyan
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