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To: "linux-btrfs@vger.kernel.org" <linux-btrfs@vger.kernel.org>
From: Stefan Priebe - Profihost AG <s.priebe@profihost.ag>
Subject: deadlock with btrfs heavy i/o and kswapd
Message-ID: <281582c9-1307-612e-77e6-9d768337ea3e@profihost.ag>
Date: Thu, 22 Sep 2016 08:41:52 +0200
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Hi,

i always encounter btrfs deadlocks / hung tasks, when i have a lot of
cached mem and i'm doing heavy rsync --inplace operations in my system
from btrfs zlib compressed disk A to btrfs zlib compressed disk B.

The last output i see in this case is kswapd0 running for a long time at
100% cpu. Then the whole system get's stuck. I cannot connect to ssh
anymore but the kernel still prints hung tasks every few minutes.

May be relevant the system has NO swap.

vm.vfs_cache_pressure = 100
vm.swappiness = 50

Greets,
Stefan