linux-kernel - Re: [PATCH 00/17] [RFC] soft and dynamic dirty throttling limits

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Date:	Wed, 13 Oct 2010 14:07:33 +1100
From:	Dave Chinner <david@...morbit.com>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Wu Fengguang <fengguang.wu@...el.com>,
	linux-mm <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Theodore Ts'o <tytso@....edu>, Jan Kara <jack@...e.cz>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Mel Gorman <mel@....ul.ie>, Rik van Riel <riel@...hat.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Chris Mason <chris.mason@...cle.com>,
	Christoph Hellwig <hch@....de>,
	Li Shaohua <shaohua.li@...el.com>
Subject: Re: [PATCH 00/17] [RFC] soft and dynamic dirty throttling limits

On Tue, Oct 12, 2010 at 10:17:16AM -0400, Christoph Hellwig wrote:
> Wu, what's the state of this series?  It looks like we'll need it
> rather sooner than later - try to get at least the preparations in
> ASAP would be really helpful.

Not ready in it's current form. This load (creating millions of 1
byte files in parallel):

$ /usr/bin/time ./fs_mark -D 10000 -S0 -n 100000 -s 1 -L 63 \
> -d /mnt/scratch/0 -d /mnt/scratch/1 \
> -d /mnt/scratch/2 -d /mnt/scratch/3 \
> -d /mnt/scratch/4 -d /mnt/scratch/5 \
> -d /mnt/scratch/6 -d /mnt/scratch/7

Locks up all the fs_mark processes spinning in traces like the
following and no further progress is made when the inode cache
fills memory.

[ 2601.452017] fs_mark       R  running task        0  2303   2235 0x00000008
[ 2601.452017]  ffff8801188f7878 ffffffff8103e2c9 ffff8801188f78a8 0000000000000000
[ 2601.452017]  0000000000000002 ffff8801129e21c0 ffff880002fd44c0 0000000000000000
[ 2601.452017]  ffff8801188f78b8 ffffffff810a9a08 ffff8801188f78e8 ffffffff810a98e5
[ 2601.452017] Call Trace:
[ 2601.452017]  [<ffffffff81060edc>] ? kvm_clock_read+0x1c/0x20
[ 2601.452017]  [<ffffffff8103e2c9>] ? sched_clock+0x9/0x10
[ 2601.452017]  [<ffffffff810a98e5>] ? sched_clock_local+0x25/0x90
[ 2601.452017]  [<ffffffff810b9e00>] ? __lock_acquire+0x330/0x14d0
[ 2601.452017]  [<ffffffff810a9a94>] ? local_clock+0x34/0x80
[ 2601.452017]  [<ffffffff81061cc8>] ? pvclock_clocksource_read+0x58/0xd0
[ 2601.452017]  [<ffffffff81061cc8>] ? pvclock_clocksource_read+0x58/0xd0
[ 2601.452017]  [<ffffffff81060edc>] ? kvm_clock_read+0x1c/0x20
[ 2601.452017]  [<ffffffff8103e2c9>] ? sched_clock+0x9/0x10
[ 2601.452017]  [<ffffffff810bb054>] ? lock_acquire+0xb4/0x140
[ 2601.452017]  [<ffffffff8103e2c9>] ? sched_clock+0x9/0x10
[ 2601.452017]  [<ffffffff810a98e5>] ? sched_clock_local+0x25/0x90
[ 2601.452017]  [<ffffffff81698ea2>] ? prop_get_global+0x32/0x50
[ 2601.452017]  [<ffffffff81699230>] ? prop_fraction_percpu+0x30/0xa0
[ 2601.452017]  [<ffffffff8111af3b>] ? bdi_dirty_limit+0x9b/0xe0
[ 2601.452017]  [<ffffffff8111bbd8>] ? balance_dirty_pages_ratelimited_nr+0x178/0x580
[ 2601.452017]  [<ffffffff81ad440b>] ? _raw_spin_unlock+0x2b/0x40
[ 2601.452017]  [<ffffffff8117ccd5>] ? __mark_inode_dirty+0xc5/0x230
[ 2601.452017]  [<ffffffff811114d5>] ? iov_iter_copy_from_user_atomic+0x95/0x170
[ 2601.452017]  [<ffffffff811118fc>] ? generic_file_buffered_write+0x1cc/0x270
[ 2601.452017]  [<ffffffff81492f2f>] ? xfs_file_aio_write+0x79f/0xaf0
[ 2601.452017]  [<ffffffff81060edc>] ? kvm_clock_read+0x1c/0x20
[ 2601.452017]  [<ffffffff81060edc>] ? kvm_clock_read+0x1c/0x20
[ 2601.452017]  [<ffffffff8103e2c9>] ? sched_clock+0x9/0x10
[ 2601.452017]  [<ffffffff810a98e5>] ? sched_clock_local+0x25/0x90
[ 2601.452017]  [<ffffffff81157cca>] ? do_sync_write+0xda/0x120
[ 2601.452017]  [<ffffffff8112e20c>] ? might_fault+0x5c/0xb0
[ 2601.452017]  [<ffffffff81669f7f>] ? security_file_permission+0x1f/0x80
[ 2601.452017]  [<ffffffff81157fb8>] ? vfs_write+0xc8/0x180
[ 2601.452017]  [<ffffffff81158904>] ? sys_write+0x54/0x90
[ 2601.452017]  [<ffffffff81037072>] ? system_call_fastpath+0x16/0x1b

This is on an 8p/4GB RAM VM.

FWIW, this one test now has a proven record of exposing writeback,
VM and filesystem regressions, so I'd suggest that anyone doing any
sort of work that affects writeback adds it to their test matrix....

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com
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