Message-ID: <52132243.8050803@profihost.ag>
Date: Tue, 20 Aug 2013 10:01:07 +0200
From: Stefan Priebe - Profihost AG <s.priebe@profihost.ag>
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To: Kent Overstreet <kmo@daterainc.com>
CC: Jens Axboe <axboe@kernel.dk>, linux-kernel@vger.kernel.org,
        linux-bcache@vger.kernel.org
Subject: Re: bcache: Fix a writeback performance regression
References: <20130814225904.GA6427@kmo-pixel> <520C788A.1060208@profihost.ag> <520DFAB4.1050402@profihost.ag> <52114614.4070509@profihost.ag> <20130819222718.GA32104@kmo-pixel>
In-Reply-To: <20130819222718.GA32104@kmo-pixel>
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Am 20.08.2013 00:27, schrieb Kent Overstreet:
> On Mon, Aug 19, 2013 at 12:09:24AM +0200, Stefan Priebe wrote:
>>
>> Vanilla 3.10.7 + bcache: Fix a writeback performance regression
>>
>> http://pastebin.com/raw.php?i=LXZk4cMH
> 
> Whoops, at first I thought this was the same bug as one I'd already been
> chasing down that had been a harmless bug - turns out I didn't look
> closely enough at the backtrace.
> 
> What happened is background writeback is deadlocking, because for some
> reason the workqueue it's running out of is a singlethreaded workqueue,
> so as soon as it decides to queue enough writeback bios that it has to
> sleep on that semaphore (which often won't happen due to the PD
> controller based ratelimiting) - boom, deadlock.
> 
> Here's the fixup patch I just tested and am applying:

thanks, this works fine. The only issue i still have, is that the
dirty_date value starts at 0 and goes to a negative value after reboot.

Greets,
Stefan
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