Re: boot warnings due to swap: make each swap partition have one address_space

Hugh Dickins
2013-01-27T02:16:12Z

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?

Hugh

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.

>
> Reported-by: Sasha Levin <sasha.levin@oracle.com>
> Signed-off-by: Shaohua Li <shli@fusionio.com>
> ---
> mm/swap.c | 1 +
> mm/swap_state.c | 11 +++++++----
> 2 files changed, 8 insertions(+), 4 deletions(-)
>
> Index: linux/mm/swap.c
> ===================================================================
> --- linux.orig/mm/swap.c 2013-01-22 10:11:58.310933234 +0800
> +++ linux/mm/swap.c 2013-01-25 12:14:49.524863610 +0800
> @@ -859,6 +859,7 @@ void __init swap_setup(void)
> int i;
>
> for (i = 0; i < MAX_SWAPFILES; i++) {
> + swapper_spaces[i].backing_dev_info += 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);
> Index: linux/mm/swap_state.c
> ===================================================================
> --- linux.orig/mm/swap_state.c 2013-01-24 18:08:05.149390977 +0800
> +++ linux/mm/swap_state.c 2013-01-25 12:14:12.849323671 +0800
> @@ -31,16 +31,19 @@ static const struct address_space_operat
> .migratepage = migrate_page,
> };
>
> -static struct backing_dev_info swap_backing_dev_info = {
> - .name = "swap",
> - .capabilities = BDI_CAP_NO_ACCT_AND_WRITEBACK | BDI_CAP_SWAP_BACKED,
> +static struct backing_dev_info swap_backing_dev_info[MAX_SWAPFILES] = {
> + [0 ... MAX_SWAPFILES - 1] = {
> + .name = "swap",
> + .capabilities = BDI_CAP_NO_ACCT_AND_WRITEBACK |
> + BDI_CAP_SWAP_BACKED,
> + }
> };
>
> struct address_space swapper_spaces[MAX_SWAPFILES] = {
> [0 ... MAX_SWAPFILES - 1] = {
> .page_tree = RADIX_TREE_INIT(GFP_ATOMIC|__GFP_NOWARN),
> .a_ops = &swap_aops,
> - .backing_dev_info = &swap_backing_dev_info,
> + .backing_dev_info = &swap_backing_dev_info[0],
> }
> };
>
>