linux-kernel - Re: boot warnings due to swap: make each swap partition have one address

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Date:	Sun, 27 Jan 2013 22:12:53 +0800
From:	Shaohua Li <shli@...nel.org>
To:	Hugh Dickins <hughd@...gle.com>
Cc:	Sasha Levin <sasha.levin@...cle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Shaohua Li <shli@...ionio.com>, Rik van Riel <riel@...hat.com>,
	Minchan Kim <minchan@...nel.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: boot warnings due to swap: make each swap partition have one
 address_space

On Sat, Jan 26, 2013 at 06:16:05PM -0800, Hugh Dickins wrote:
> On Fri, 25 Jan 2013, Shaohua Li wrote:
> > On Thu, Jan 24, 2013 at 10:45:57PM -0500, Sasha Levin wrote:
> > > Hi folks,
> > > 
> > > Commit "swap: make each swap partition have one address_space" is triggering
> > > a series of warnings on boot:
> > > 
> > > [    3.446071] ------------[ cut here ]------------
> > > [    3.446664] WARNING: at lib/debugobjects.c:261 debug_print_object+0x8e/0xb0()
> > > [    3.447715] ODEBUG: init active (active state 0) object type: percpu_counter hint:           (null)
> > > [    3.450360] Modules linked in:
> > > [    3.451593] Pid: 1, comm: swapper/0 Tainted: G        W    3.8.0-rc4-next-20130124-sasha-00004-g838a1b4 #266
> > > [    3.454508] Call Trace:
> > > [    3.455248]  [<ffffffff8110d1bc>] warn_slowpath_common+0x8c/0xc0
> > > [    3.455248]  [<ffffffff8110d291>] warn_slowpath_fmt+0x41/0x50
> > > [    3.455248]  [<ffffffff81a2bb5e>] debug_print_object+0x8e/0xb0
> > > [    3.455248]  [<ffffffff81a2c26b>] __debug_object_init+0x20b/0x290
> > > [    3.455248]  [<ffffffff81a2c305>] debug_object_init+0x15/0x20
> > > [    3.455248]  [<ffffffff81a3fbed>] __percpu_counter_init+0x6d/0xe0
> > > [    3.455248]  [<ffffffff81231bdc>] bdi_init+0x1ac/0x270
> > > [    3.455248]  [<ffffffff8618f20b>] swap_setup+0x3b/0x87
> > > [    3.455248]  [<ffffffff8618f257>] ? swap_setup+0x87/0x87
> > > [    3.455248]  [<ffffffff8618f268>] kswapd_init+0x11/0x7c
> > > [    3.455248]  [<ffffffff810020ca>] do_one_initcall+0x8a/0x180
> > > [    3.455248]  [<ffffffff86168cfd>] do_basic_setup+0x96/0xb4
> > > [    3.455248]  [<ffffffff861685ae>] ? loglevel+0x31/0x31
> > > [    3.455248]  [<ffffffff861885cd>] ? sched_init_smp+0x150/0x157
> > > [    3.455248]  [<ffffffff86168ded>] kernel_init_freeable+0xd2/0x14c
> > > [    3.455248]  [<ffffffff83cade10>] ? rest_init+0x140/0x140
> > > [    3.455248]  [<ffffffff83cade19>] kernel_init+0x9/0xf0
> > > [    3.455248]  [<ffffffff83d5727c>] ret_from_fork+0x7c/0xb0
> > > [    3.455248]  [<ffffffff83cade10>] ? rest_init+0x140/0x140
> > > [    3.455248] ---[ end trace 0b176d5c0f21bffb ]---
> > > 
> > > I haven't looked deeper into it yet, and will do so tomorrow, unless this
> > > spew is obvious to anyone.
> > 
> > Does this one help?
> > 
> > Subject: give-each-swapper-space-separate-backing_dev_info
> > 
> > The backing_dev_info can't be shared by all swapper address space.
> 
> Whyever not?  It's perfectly normal for different inodes/address_spaces
> to share a single backing_dev!  Sasha's trace says that it's wrong to
> initialize it MAX_SWAPFILES times: fair enough.  But why should I now
> want to spend 32kB (not even counting their __percpu counters) on all
> these pseudo-backing_devs?

That's correct, silly me. Updated it.
> 
> p.s. a grand little change would be to move page_cluster and swap_setup()
> from mm/swap.c to mm/swap_state.c: they have nothing to do with the other
> contents of swap.c, and everything to do with the contents of swap_state.c.
> Why swap.c is called swap.c is rather a mystery.

Tried, but looks page_cluster is used in sysctl, moving to swap_state.c will
make it optional. don't want to add another #ifdef, so give up.


Subject: init-swap-space-backing-dev-info-once


Sasha reported:
Commit "swap: make each swap partition have one address_space" is triggering
a series of warnings on boot:

[    3.446071] ------------[ cut here ]------------
[    3.446664] WARNING: at lib/debugobjects.c:261 debug_print_object+0x8e/0xb0()
[    3.447715] ODEBUG: init active (active state 0) object type: percpu_counter hint:           (null)
[    3.450360] Modules linked in:
[    3.451593] Pid: 1, comm: swapper/0 Tainted: G        W    3.8.0-rc4-next-20130124-sasha-00004-g838a1b4 #266
[    3.454508] Call Trace:
[    3.455248]  [<ffffffff8110d1bc>] warn_slowpath_common+0x8c/0xc0
[    3.455248]  [<ffffffff8110d291>] warn_slowpath_fmt+0x41/0x50
[    3.455248]  [<ffffffff81a2bb5e>] debug_print_object+0x8e/0xb0
[    3.455248]  [<ffffffff81a2c26b>] __debug_object_init+0x20b/0x290
[    3.455248]  [<ffffffff81a2c305>] debug_object_init+0x15/0x20
[    3.455248]  [<ffffffff81a3fbed>] __percpu_counter_init+0x6d/0xe0
[    3.455248]  [<ffffffff81231bdc>] bdi_init+0x1ac/0x270
[    3.455248]  [<ffffffff8618f20b>] swap_setup+0x3b/0x87
[    3.455248]  [<ffffffff8618f257>] ? swap_setup+0x87/0x87
[    3.455248]  [<ffffffff8618f268>] kswapd_init+0x11/0x7c
[    3.455248]  [<ffffffff810020ca>] do_one_initcall+0x8a/0x180
[    3.455248]  [<ffffffff86168cfd>] do_basic_setup+0x96/0xb4
[    3.455248]  [<ffffffff861685ae>] ? loglevel+0x31/0x31
[    3.455248]  [<ffffffff861885cd>] ? sched_init_smp+0x150/0x157
[    3.455248]  [<ffffffff86168ded>] kernel_init_freeable+0xd2/0x14c
[    3.455248]  [<ffffffff83cade10>] ? rest_init+0x140/0x140
[    3.455248]  [<ffffffff83cade19>] kernel_init+0x9/0xf0
[    3.455248]  [<ffffffff83d5727c>] ret_from_fork+0x7c/0xb0
[    3.455248]  [<ffffffff83cade10>] ? rest_init+0x140/0x140
[    3.455248] ---[ end trace 0b176d5c0f21bffb ]---

Initialize swap space backing_dev_info once to avoid the warning.

Reported-by: Sasha Levin <sasha.levin@...cle.com>
Signed-off-by: Shaohua Li <shli@...ionio.com>
---
 mm/swap.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Index: linux/mm/swap.c
===================================================================
--- linux.orig/mm/swap.c	2013-01-27 21:26:21.942696713 +0800
+++ linux/mm/swap.c	2013-01-27 21:27:29.233865394 +0800
@@ -858,8 +858,8 @@ void __init swap_setup(void)
 #ifdef CONFIG_SWAP
 	int i;
 
+	bdi_init(swapper_spaces[0].backing_dev_info);
 	for (i = 0; i < MAX_SWAPFILES; i++) {
-		bdi_init(swapper_spaces[i].backing_dev_info);
 		spin_lock_init(&swapper_spaces[i].tree_lock);
 		INIT_LIST_HEAD(&swapper_spaces[i].i_mmap_nonlinear);
 	}
--
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