linux-kernel - Re: Unexpected slow block device write IO performance compared to uncached, unsynced direct IO using stock kernels

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Message-ID: <20150902141223.GA31906@altium.nl>
Date:	Wed, 2 Sep 2015 16:12:23 +0200
From:	Dick Streefland <dick.streefland@...ium.nl>
To:	Erik Cumps <erik.cumps@...turnus.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: Unexpected slow block device write IO performance compared to
 uncached, unsynced direct IO using stock kernels

On Tuesday 2015-09-01 11:15, Dick Streefland wrote:
| I'm seeing this as well here on a number of new Dell Optiplex 7020
| machines and one older Optiplex 780, all with 8GB RAM and running
| Ubuntu 14.04 in 32-bit mode.

It turned out that the dirty thresholds in /proc/vmstat became zero:

nr_dirty_threshold 0
nr_dirty_background_threshold 0

A workaround is:

# sysctl vm.highmem_is_dirtyable=1

-- 
Dick
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