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

From	Dick Streefland <dick.streefland@altium.nl>
Newsgroups	linux.kernel
Subject	Re: Unexpected slow block device write IO performance compared to uncached, unsynced direct IO using stock kernels
Date	2015-09-02 16:20 +0200
Message-ID	<q4h3j-7tc-11@gated-at.bofh.it> (permalink)
References	<pBZzc-4ci-3@gated-at.bofh.it> <pBZzc-4ci-3@gated-at.bofh.it> <pCCAy-1Mb-21@gated-at.bofh.it> <q3Qmu-2NS-11@gated-at.bofh.it>
Organization	Altium BV, Amersfoort, The Netherlands

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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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Re: Unexpected slow block device write IO performance compared to  uncached, unsynced direct IO using stock kernels Dick Streefland <dick.streefland@altium.nl> - 2015-09-01 11:50 +0200
  Re: Unexpected slow block device write IO performance compared to  uncached, unsynced direct IO using stock kernels Dick Streefland <dick.streefland@altium.nl> - 2015-09-02 16:20 +0200

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