linux-ext4 - Re: [RFC PATCH] fstests: Check if a fs can survive random (emulated) power loss

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Date:   Mon, 26 Feb 2018 16:50:20 +0800
From:   Qu Wenruo <quwenruo.btrfs@....com>
To:     Amir Goldstein <amir73il@...il.com>
Cc:     Qu Wenruo <wqu@...e.com>, fstests <fstests@...r.kernel.org>,
        Linux Btrfs <linux-btrfs@...r.kernel.org>,
        linux-xfs <linux-xfs@...r.kernel.org>,
        Ext4 <linux-ext4@...r.kernel.org>,
        Josef Bacik <josef@...icpanda.com>
Subject: Re: [RFC PATCH] fstests: Check if a fs can survive random (emulated)
 power loss



On 2018年02月26日 16:45, Amir Goldstein wrote:
> On Mon, Feb 26, 2018 at 10:41 AM, Qu Wenruo <quwenruo.btrfs@....com> wrote:
>>
>>
>> On 2018年02月26日 16:33, Amir Goldstein wrote:
>>> On Mon, Feb 26, 2018 at 10:20 AM, Qu Wenruo <quwenruo.btrfs@....com> wrote:
>>>>
>>>>
>>>> On 2018年02月26日 16:15, Amir Goldstein wrote:
>>>>> On Mon, Feb 26, 2018 at 9:31 AM, Qu Wenruo <wqu@...e.com> wrote:
>>>>>> This test case is originally designed to expose unexpected corruption
>>>>>> for btrfs, where there are several reports about btrfs serious metadata
>>>>>> corruption after power loss.
>>>>>>
>>>>>> The test case itself will trigger heavy fsstress for the fs, and use
>>>>>> dm-flakey to emulate power loss by dropping all later writes.
>>>>>>
>>>>>
>>>>> Come on... dm-flakey is so 2016
>>>>> You should take Josef's fsstress+log-writes test and bring it to fstests:
>>>>> https://github.com/josefbacik/log-writes
>>>>>
>>>>> By doing that you will gain two very important features from the test:
>>>>>
>>>>> 1. Problems will be discovered much faster, because the test can run fsck
>>>>>     after every single block write has been replayed instead of just at random
>>>>>     times like in your test
>>>>
>>>> That's what exactly I want!!!
>>>>
>>>> Great thanks for this one! I would definitely look into this.
>>>> (Although the initial commit is even older than 2016)
>>>>
>>>
>>> Please note that Josef's replay-individual-faster.sh script runs fsck
>>> every 1000 writes (i.e. --check 1000), so you can play with this argument
>>> in your test. Can also run --fsck every --check fua or --check flush, which
>>> may be more indicative of real world problems. not sure.
>>>
>>>>
>>>> But the test itself could already expose something on EXT4, it still
>>>> makes some sense for ext4 developers as a verification test case.
>>>>
>>>
>>> Please take a look at generic/456
>>> When generic/455 found a reproduciable problem in ext4,
>>> I created a specific test without any randomness to pin point the
>>> problem found (using dm-flakey).
>>> If the problem you found is reproduciable, then it will be easy for you
>>> to create a similar "bisected" test.
>>
>> Yep, it's definitely needed for a pin-point test case, but I'm also
>> wondering if a random, stress test could also help.
>>
>> Test case with plain fsstress is already super helpful to expose some
>> bugs, such stress test won't hurt.
>>
> 
> 
> Yes, but the same stress test with dm-log-writes instead of dm-flakey
> will be as useful and much more, so no reason to merge the less useful
> stress test.

OK, I'll try to use dm-log to enhance the test case.

Thanks,
Qu

> 
> Thanks,
> Amir.
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