From: Roman Mamedov <rm@romanrm.net>
To: Robert Kierski <rkierski@cray.com>
Cc: Adam Goryachev <adam@websitemanagers.com.au>,
"linux-raid@vger.kernel.org" <linux-raid@vger.kernel.org>
Subject: Re: stripe_cache_active always 0
Date: Thu, 7 Jan 2016 22:52:43 +0500 [thread overview]
Message-ID: <20160107225243.74f5549b@natsu> (raw)
In-Reply-To: <F7761B9B1D11B64BBB666019E9378117FE848B@CFWEX01.americas.cray.com>
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On Thu, 7 Jan 2016 16:34:36 +0000
Robert Kierski <rkierski@cray.com> wrote:
> As far as adjusting stripe_cache_size... The stripe cache is dynamically allocated. It won't save any RAM by decreasing stripe_cache_size.
Since when?
# echo 512 > /sys/devices/virtual/block/md0/md/stripe_cache_size
# free
total used free shared buffers cached
Mem: 16159912 15672696 487216 12588 52 14484708
-/+ buffers/cache: 1187936 14971976
Swap: 0 0 0
# echo 32768 > /sys/devices/virtual/block/md0/md/stripe_cache_size
# free
total used free shared buffers cached
Mem: 16159912 15957880 202032 12588 52 14214952
-/+ buffers/cache: 1742876 14417036
Swap: 0 0 0
You can see that's not the case (on kernel 4.3.3 with four-member RAID5);
And it's quite easy to rapidly hit OOM issues on high-member-count arrays by
setting stripe_cache_size to larger values (not realizing that this is *in
pages* not kilobytes or sectors, and *per disk*).
As for the original question, try checking stripe_cache_active e.g. once
per second during heavy write load to the filesystem.
--
With respect,
Roman
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next prev parent reply other threads:[~2016-01-07 17:52 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-01-07 3:09 stripe_cache_active always 0 Adam Goryachev
2016-01-07 16:34 ` Robert Kierski
2016-01-07 17:52 ` Roman Mamedov [this message]
2016-01-07 17:53 ` {Possible Spam} " Benjamin ESTRABAUD
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