linux-kernel - Re: [PATCH] blk-wbt: Avoid lock contention and thundering herd issue in wbt

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Message-ID: <834649ab-62d6-bc7f-ec60-6c1654ea3f26@applied-asynchrony.com>
Date:   Wed, 22 Aug 2018 14:54:15 +0200
From:   Holger Hoffstätte <holger@...lied-asynchrony.com>
To:     Jens Axboe <axboe@...nel.dk>, Anchal Agarwal <anchalag@...zon.com>
Cc:     fllinden@...zon.com, sblbir@...zon.com, msw@...zon.com,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] blk-wbt: Avoid lock contention and thundering herd issue
 in wbt_wait

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.

-h