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Subject: Re: [PATCH] blk-wbt: Avoid lock contention and thundering herd issue
 in wbt_wait
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From:   Jens Axboe <axboe@kernel.dk>
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Date:   Wed, 22 Aug 2018 08:27:04 -0600
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On 8/22/18 6:54 AM, Holger Hoffstätte wrote:
> On 08/22/18 06:10, Jens Axboe wrote:
>> [...]
>> If you have time, please look at the 3 patches I posted earlier today.
>> Those are for mainline, so should be OK :-)
> 
> I'm just playing along at home but with those 3 I get repeatable
> hangs & writeback not starting at all, but curiously *only* on my btrfs
> device; for inexplicable reasons some other devices with ext4/xfs flush
> properly. Yes, that surprised me too, but it's repeatable.
> Now this may or may not have something to do with some of my in-testing
> patches for btrfs itself, but if I remove those 3 wbt fixes, everything
> is golden again. Not eager to repeat since it hangs sync & requires a
> hard reboot.. :(
> Just thought you'd like to know.

Thanks, that's very useful info! I'll see if I can reproduce that.

-- 
Jens Axboe