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Date: Sun, 18 Sep 2011 22:17:05 +0800
From: Wu Fengguang <fengguang.wu@...el.com>
To: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc: "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Jan Kara <jack@...e.cz>, Christoph Hellwig <hch@....de>,
Dave Chinner <david@...morbit.com>,
Greg Thelen <gthelen@...gle.com>,
Minchan Kim <minchan.kim@...il.com>,
Vivek Goyal <vgoyal@...hat.com>,
Andrea Righi <arighi@...eler.com>,
linux-mm <linux-mm@...ck.org>,
LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 10/18] writeback: dirty position control - bdi reserve
area
On Mon, Sep 12, 2011 at 06:19:38PM +0800, Peter Zijlstra wrote:
> On Wed, 2011-09-07 at 20:31 +0800, Wu Fengguang wrote:
> > > > + x_intercept = min(write_bw, freerun);
> > > > + if (bdi_dirty < x_intercept) {
> > >
> > > So the point of the freerun point is that we never throttle before it,
> > > so basically all the below shouldn't be needed at all, right?
> >
> > Yes!
> >
> > > > + if (bdi_dirty > x_intercept / 8) {
> > > > + pos_ratio *= x_intercept;
> > > > + do_div(pos_ratio, bdi_dirty);
> > > > + } else
> > > > + pos_ratio *= 8;
> > > > + }
> > > > +
> > > > return pos_ratio;
> > > > }
>
> Does that mean we can remove this whole block?
Right, if the bdi freerun concept is proved to work fine.
Unfortunately I find it mostly yields lower performance than bdi
reserve area. Patch is attached. If you would like me try other
patches, I can easily kick off new tests and redo the comparison.
Here is the nr_written numbers over various JBOD test cases,
the larger, the better:
bdi-reserve bdi-freerun diff case
---------------------------------------------------------------------------------------
38375271 31553807 -17.8% JBOD-10HDD-6G/xfs-100dd-1M-16p-5895M-20
30478879 28631491 -6.1% JBOD-10HDD-6G/xfs-10dd-1M-16p-5895M-20
29735407 28871956 -2.9% JBOD-10HDD-6G/xfs-1dd-1M-16p-5895M-20
30850350 28344165 -8.1% JBOD-10HDD-6G/xfs-2dd-1M-16p-5895M-20
17706200 16174684 -8.6% JBOD-10HDD-thresh=100M/xfs-100dd-1M-16p-5895M-100M
23374918 14376942 -38.5% JBOD-10HDD-thresh=100M/xfs-10dd-1M-16p-5895M-100M
20659278 19640375 -4.9% JBOD-10HDD-thresh=100M/xfs-1dd-1M-16p-5895M-100M
22517497 14552321 -35.4% JBOD-10HDD-thresh=100M/xfs-2dd-1M-16p-5895M-100M
68287850 61078553 -10.6% JBOD-10HDD-thresh=2G/xfs-100dd-1M-16p-5895M-2048M
33835247 32018425 -5.4% JBOD-10HDD-thresh=2G/xfs-10dd-1M-16p-5895M-2048M
30187817 29942083 -0.8% JBOD-10HDD-thresh=2G/xfs-1dd-1M-16p-5895M-2048M
30563144 30204022 -1.2% JBOD-10HDD-thresh=2G/xfs-2dd-1M-16p-5895M-2048M
34476862 34645398 +0.5% JBOD-10HDD-thresh=4G/xfs-10dd-1M-16p-5895M-4096M
30326479 30097263 -0.8% JBOD-10HDD-thresh=4G/xfs-1dd-1M-16p-5895M-4096M
30446767 30339683 -0.4% JBOD-10HDD-thresh=4G/xfs-2dd-1M-16p-5895M-4096M
40793956 45936678 +12.6% JBOD-10HDD-thresh=800M/xfs-100dd-1M-16p-5895M-800M
27481305 24867282 -9.5% JBOD-10HDD-thresh=800M/xfs-10dd-1M-16p-5895M-800M
25651257 22507406 -12.3% JBOD-10HDD-thresh=800M/xfs-1dd-1M-16p-5895M-800M
19849350 21298787 +7.3% JBOD-10HDD-thresh=800M/xfs-2dd-1M-16p-5895M-800M
raw data by "grep":
JBOD-10HDD-6G/xfs-100dd-1M-16p-5895M-20:10-3.1.0-rc4+/vmstat-end:nr_written 38375271
JBOD-10HDD-6G/xfs-10dd-1M-16p-5895M-20:10-3.1.0-rc4+/vmstat-end:nr_written 30478879
JBOD-10HDD-6G/xfs-1dd-1M-16p-5895M-20:10-3.1.0-rc4+/vmstat-end:nr_written 29735407
JBOD-10HDD-6G/xfs-2dd-1M-16p-5895M-20:10-3.1.0-rc4+/vmstat-end:nr_written 30850350
JBOD-10HDD-thresh=100M/xfs-100dd-1M-16p-5895M-100M:10-3.1.0-rc4+/vmstat-end:nr_written 17706200
JBOD-10HDD-thresh=100M/xfs-10dd-1M-16p-5895M-100M:10-3.1.0-rc4+/vmstat-end:nr_written 23374918
JBOD-10HDD-thresh=100M/xfs-1dd-1M-16p-5895M-100M:10-3.1.0-rc4+/vmstat-end:nr_written 20659278
JBOD-10HDD-thresh=100M/xfs-2dd-1M-16p-5895M-100M:10-3.1.0-rc4+/vmstat-end:nr_written 22517497
JBOD-10HDD-thresh=2G/xfs-100dd-1M-16p-5895M-2048M:10-3.1.0-rc4+/vmstat-end:nr_written 68287850
JBOD-10HDD-thresh=2G/xfs-10dd-1M-16p-5895M-2048M:10-3.1.0-rc4+/vmstat-end:nr_written 33835247
JBOD-10HDD-thresh=2G/xfs-1dd-1M-16p-5895M-2048M:10-3.1.0-rc4+/vmstat-end:nr_written 30187817
JBOD-10HDD-thresh=2G/xfs-2dd-1M-16p-5895M-2048M:10-3.1.0-rc4+/vmstat-end:nr_written 30563144
JBOD-10HDD-thresh=4G/xfs-10dd-1M-16p-5895M-4096M:10-3.1.0-rc4+/vmstat-end:nr_written 34476862
JBOD-10HDD-thresh=4G/xfs-1dd-1M-16p-5895M-4096M:10-3.1.0-rc4+/vmstat-end:nr_written 30326479
JBOD-10HDD-thresh=4G/xfs-2dd-1M-16p-5895M-4096M:10-3.1.0-rc4+/vmstat-end:nr_written 30446767
JBOD-10HDD-thresh=800M/xfs-100dd-1M-16p-5895M-800M:10-3.1.0-rc4+/vmstat-end:nr_written 40793956
JBOD-10HDD-thresh=800M/xfs-10dd-1M-16p-5895M-800M:10-3.1.0-rc4+/vmstat-end:nr_written 27481305
JBOD-10HDD-thresh=800M/xfs-1dd-1M-16p-5895M-800M:10-3.1.0-rc4+/vmstat-end:nr_written 25651257
JBOD-10HDD-thresh=800M/xfs-2dd-1M-16p-5895M-800M:10-3.1.0-rc4+/vmstat-end:nr_written 19849350
JBOD-10HDD-6G/xfs-100dd-1M-16p-5895M-20:10-3.1.0-rc4-bdi-freerun+/vmstat-end:nr_written 31553807
JBOD-10HDD-6G/xfs-10dd-1M-16p-5895M-20:10-3.1.0-rc4-bdi-freerun+/vmstat-end:nr_written 28631491
JBOD-10HDD-6G/xfs-1dd-1M-16p-5895M-20:10-3.1.0-rc4-bdi-freerun+/vmstat-end:nr_written 28871956
JBOD-10HDD-6G/xfs-2dd-1M-16p-5895M-20:10-3.1.0-rc4-bdi-freerun+/vmstat-end:nr_written 28344165
JBOD-10HDD-thresh=100M/xfs-100dd-1M-16p-5895M-100M:10-3.1.0-rc4-bdi-freerun+/vmstat-end:nr_written 16174684
JBOD-10HDD-thresh=100M/xfs-10dd-1M-16p-5895M-100M:10-3.1.0-rc4-bdi-freerun+/vmstat-end:nr_written 14376942
JBOD-10HDD-thresh=100M/xfs-1dd-1M-16p-5895M-100M:10-3.1.0-rc4-bdi-freerun+/vmstat-end:nr_written 19640375
JBOD-10HDD-thresh=100M/xfs-2dd-1M-16p-5895M-100M:10-3.1.0-rc4-bdi-freerun+/vmstat-end:nr_written 14552321
JBOD-10HDD-thresh=2G/xfs-100dd-1M-16p-5895M-2048M:10-3.1.0-rc4-bdi-freerun+/vmstat-end:nr_written 61078553
JBOD-10HDD-thresh=2G/xfs-10dd-1M-16p-5895M-2048M:10-3.1.0-rc4-bdi-freerun+/vmstat-end:nr_written 32018425
JBOD-10HDD-thresh=2G/xfs-1dd-1M-16p-5895M-2048M:10-3.1.0-rc4-bdi-freerun+/vmstat-end:nr_written 29942083
JBOD-10HDD-thresh=2G/xfs-2dd-1M-16p-5895M-2048M:10-3.1.0-rc4-bdi-freerun+/vmstat-end:nr_written 30204022
JBOD-10HDD-thresh=4G/xfs-10dd-1M-16p-5895M-4096M:10-3.1.0-rc4-bdi-freerun+/vmstat-end:nr_written 34645398
JBOD-10HDD-thresh=4G/xfs-1dd-1M-16p-5895M-4096M:10-3.1.0-rc4-bdi-freerun+/vmstat-end:nr_written 30097263
JBOD-10HDD-thresh=4G/xfs-2dd-1M-16p-5895M-4096M:10-3.1.0-rc4-bdi-freerun+/vmstat-end:nr_written 30339683
JBOD-10HDD-thresh=800M/xfs-100dd-1M-16p-5895M-800M:10-3.1.0-rc4-bdi-freerun+/vmstat-end:nr_written 45936678
JBOD-10HDD-thresh=800M/xfs-10dd-1M-16p-5895M-800M:10-3.1.0-rc4-bdi-freerun+/vmstat-end:nr_written 24867282
JBOD-10HDD-thresh=800M/xfs-1dd-1M-16p-5895M-800M:10-3.1.0-rc4-bdi-freerun+/vmstat-end:nr_written 22507406
JBOD-10HDD-thresh=800M/xfs-2dd-1M-16p-5895M-800M:10-3.1.0-rc4-bdi-freerun+/vmstat-end:nr_written 21298787
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