From mboxrd@z Thu Jan 1 00:00:00 1970 From: Emmanuel Florac Subject: bcache and load average Date: Fri, 15 May 2015 18:50:32 +0200 Message-ID: <20150515185032.6b129595@harpe.intellique.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Return-path: Received: from smtpfb1-g21.free.fr ([212.27.42.9]:46744 "EHLO smtpfb1-g21.free.fr" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753443AbbEOQud (ORCPT ); Fri, 15 May 2015 12:50:33 -0400 Received: from smtp5-g21.free.fr (smtp5-g21.free.fr [212.27.42.5]) by smtpfb1-g21.free.fr (Postfix) with ESMTP id 8F6D17943CB for ; Fri, 15 May 2015 18:50:29 +0200 (CEST) Received: from harpe.intellique.com (unknown [82.225.196.72]) by smtp5-g21.free.fr (Postfix) with ESMTP id F2047D480CD for ; Fri, 15 May 2015 18:46:35 +0200 (CEST) Sender: linux-bcache-owner@vger.kernel.org List-Id: linux-bcache@vger.kernel.org To: linux-bcache@vger.kernel.org Hi everyone, Going through various forum messages and bug reports (for Debian: https://lists.debian.org/debian-kernel/2015/03/msg00060.html for Arch: https://bugs.archlinux.org/task/38843 for some other distro: https://groups.google.com/forum/#!msg/esos-users/NXp8tG7sVE8/QXZyPdZ2saIJ ) it looks like the bcache_writeback kernel thread, being in uninterruptible sleep, keeps the load average at 1.0 (or maybe more) always. Could you please confirm this ? - this behaviour should be described in the bcache documentation because it feels to me (and many other) like a true gotcha. It's apparently completely undocumented. A "CAVEATS" section at the bottom of bcache.txt in the kernel Documentation explaining this would be nice, what do you think? - Is there any way around this? Some people seem to grow uneasy (maybe irrationnally) having a constant load on an otherwise unused system (I know that a sleeping thread actually does nothing, but many system administrators can't wrap their head around this idea). I've tried some advice I've found on the web, like switching to writethrough and "echo 0 > /sys/block/bcache0/bcache/writeback_running" but to absolutely no effect. Any advice and idea is welcome :) -- ------------------------------------------------------------------------ Emmanuel Florac | Direction technique | Intellique | | +33 1 78 94 84 02 ------------------------------------------------------------------------