linux-ext4 - Re: [PATCH v2 3/3] fstests: generic: Check the fs after each FUA writes

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Date:   Wed, 28 Mar 2018 14:55:22 +0800
From:   Qu Wenruo <quwenruo.btrfs@....com>
To:     Eryu Guan <guaneryu@...il.com>
Cc:     Amir Goldstein <amir73il@...il.com>, Qu Wenruo <wqu@...e.com>,
        Linux Btrfs <linux-btrfs@...r.kernel.org>,
        fstests <fstests@...r.kernel.org>,
        linux-xfs <linux-xfs@...r.kernel.org>,
        Ext4 <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH v2 3/3] fstests: generic: Check the fs after each FUA
 writes



On 2018年03月28日 14:19, Eryu Guan wrote:
> On Wed, Mar 28, 2018 at 01:51:44PM +0800, Qu Wenruo wrote:
>>
>>
>> On 2018年03月28日 13:04, Amir Goldstein wrote:
>>> On Wed, Mar 28, 2018 at 7:40 AM, Qu Wenruo <wqu@...e.com> wrote:
>>>> Basic test case which triggers fsstress with dm-log-writes, and then
>>>> check the fs after each FUA writes.
>>>> With needed infrastructure and special handlers for journal based fs.
>>>>
>>>> Signed-off-by: Qu Wenruo <wqu@...e.com>
>>>> ---
>>>> changelog:
>>>> v2:
>>>>   Use proper "SUSE Linux Products GmbH" instead of "SuSE"
>>>>   Get rid of dm-snapshot which is pretty slow if we're creating and
>>>>   deleting snapshots repeatedly.
>>>>   (Maybe LVM thin provision would be much better, but current replay
>>>>    solution is good so far, and no slower than dm-snapshot)
>>>>   Add back run_check so that we can get the seed.
>>>> ---
>>>> Unfortunately, neither xfs nor ext4 survies this test for even single
>>>> success, while btrfs survives.
>>>> (Although not what I want, I'm just trying my luck
>>>> to reproduce a serious btrfs corruption situation)
>>>>
>>>> Although btrfs may be the fastest fs for the test, since it has fixed
>>>> small amount of write in mkfs and almost nothing to replay, it still
>>>> takes about 240s~300s to finish (the same level using snapshot).
>>>>
>>>> It would take longer time for ext4 for its large amount of write during
>>>> mkfs, if it can survive the test in the first space.
>>>
>>> Hmm, how much time would the total test would take if you don't fail
>>> it on fsck? I am asking because it may be possible to improve this with
>>> only a single snapshot after mkfs.
>>
>> The only fs which can pass the test right now is btrfs, so other
>> estimation is mostly based on guess.
>>
>>>
>>> Anyway, if total test run time is expected to be under 10min I wouldn't
>>> bother with this optimization, at least not right now. IMO it is more
>>> important to get the test out there to get the corruption bugs floating.
>>
>> I'd say from current status, if XFS doesn't fail, it would definitely
>> finish in 10min.
>> For EXT4 I'm not pretty sure.
>                                                                                                                                                                                                
> 10min might be a bit long, 5min would be good enough. I may need to
> adjust the fsstress "-n" param based on test results when I got some
> time, hopefully this week..
> 
> And I noticed that fsstress "-p" is based on nr_cpus, I'd like to cap it
> with a max allowed number, so test won't run for too long on hosts with
> hundreds of cpus. It could always be scaled with _scale_fsstress_args.
> 
> +nr_cpus=$("$here/src/feature" -o)
> +fsstress_args=$(_scale_fsstress_args -w -d $SCRATCH_MNT -n 512 -p $nr_cpus \
> +               $FSSTRESS_AVOID)

This makes sense.

(I used to think 4 cores was enough and now mainstream desktop is push 8
cores)

Thanks,
Qu

> 
>>
>> I'd like to  keep current test case as simple as possible right now, and
>> for later enhancement, I have several different ideas:
> 
> Please make new tests then :)
> 
>>
>> 1) Reflink fs + loopback
>>    Yep, use btrfs/xfs as base filesystem and create copy using reflink,
>>    then use such files as loopback device.
>>    The good thing is, AFAIK btrfs/xfs reflink is really fast.
>>    Much much faster than dm-snapshot or even LVM thin.
>>
>>    The much much smaller block size (4K default) makes CoW overhead
>>    (LVM thin is 64K, not sure about dm-snapshot though).
>>
>>    The problem is, such setup needs extra mount point and can be a
>>    little hard to setup, and we're introducing another layer of fs,
>>    if the fs itself has some hidden bug, it would screw up the test
>>    case.
>>
>> 2) LVM thin provision
>>    LVM thin provision looks much like btrfs/xfs for block level, and
>>    smaller default block size (64K vs original 2M) makes CoW overhead
>>    smaller.
>>
>>    I'm currently testing this method, the good thing is it's a little
>>    easier to setup and we can use single mount point.
>>
>> Anyway, with proper and efficient snapshot ability implemented, I will
>> definitely convert this test case, and add Flush test case.
>>
>> Thanks for your review too,
>> Qu
>>
>>>
>>> Thanks for working on this!
>>> You can add
>>> Reviewed-by: Amir Goldstein <amir73il@...il.com>
> 
> Thank you both!
> 
> Eryu
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