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Wed, 22 Aug 2018 07:27:05 -0700 (PDT) Subject: Re: [PATCH] blk-wbt: Avoid lock contention and thundering herd issue in wbt_wait To: =?UTF-8?Q?Holger_Hoffst=c3=a4tte?= , Anchal Agarwal Cc: fllinden@amazon.com, sblbir@amazon.com, msw@amazon.com, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org References: <6bab69c9-b787-b12f-7738-72e05bf74444@kernel.dk> <72f90be2-0b63-d3a0-e953-da9232f44d5b@kernel.dk> <761bb0ab416649b8bf3bac1706124456@EX13D13UWB002.ant.amazon.com> <7f6c399d-bda1-0bbf-4ea1-07fc510ed1eb@kernel.dk> <3498fbfb-e9f3-7606-1fc3-904a0e61ff57@kernel.dk> <168d80ac73a44a6f9242c47c164778fc@EX13D13UWB002.ant.amazon.com> <20180820224241.GA72523@8c8590bceeee.ant.amazon.com> <70e2063a-53fa-2475-eed9-07db277c8c0d@kernel.dk> <20180822040126.GA18736@kaos-source-ops-60001.pdx1.amazon.com> <76ecb022-f167-67eb-8801-111fc209bbaa@kernel.dk> <834649ab-62d6-bc7f-ec60-6c1654ea3f26@applied-asynchrony.com> From: Jens Axboe Message-ID: Date: Wed, 22 Aug 2018 08:27:04 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.0 MIME-Version: 1.0 In-Reply-To: <834649ab-62d6-bc7f-ec60-6c1654ea3f26@applied-asynchrony.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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