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Message-Id: <20110121145222.82694908.nishimura@mxp.nes.nec.co.jp>
Date: Fri, 21 Jan 2011 14:52:22 +0900
From: Daisuke Nishimura <nishimura@....nes.nec.co.jp>
To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Miklos Szeredi <miklos@...redi.hu>, minchan.kim@...il.com,
linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
linux-kernel@...r.kernel.org,
Daisuke Nishimura <nishimura@....nes.nec.co.jp>
Subject: Re: [PATCH v4] mm: add replace_page_cache_page() function
On Wed, 19 Jan 2011 10:23:48 +0900
KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> wrote:
> On Wed, 19 Jan 2011 10:11:12 +0900
> nishimura@....nes.nec.co.jp wrote:
>
> > > On Wed, 19 Jan 2011 09:27:33 +0900
> > > Daisuke Nishimura <nishimura@....nes.nec.co.jp> wrote:
> > >
> > >> On Tue, 18 Jan 2011 15:28:44 -0800
> > >> Andrew Morton <akpm@...ux-foundation.org> wrote:
> > >>
> > >> > On Tue, 18 Jan 2011 12:18:11 +0100
> > >> > Miklos Szeredi <miklos@...redi.hu> wrote:
> > >> >
> > >> > > +int replace_page_cache_page(struct page *old, struct page *new, gfp_t gfp_mask)
> > >> > > +{
> > >> > > + int error;
> > >> > > + struct mem_cgroup *memcg = NULL;
> > >> >
> > >> > I'm suspecting that the unneeded initialisation was added to suppress a
> > >> > warning?
> > >> >
> > >> No.
> > >> It's necessary for mem_cgroup_{prepare|end}_migration().
> > >> mem_cgroup_prepare_migration() will return without doing anything in
> > >> "if (mem_cgroup_disabled()" case(iow, "memcg" is not overwritten),
> > >> but mem_cgroup_end_migration() depends on the value of "memcg" to decide
> > >> whether prepare_migration has succeeded or not.
> > >> This may not be a good implementation, but IMHO I'd like to to initialize
> > >> valuable before using it in general.
> > >>
> > >
> > > I think it can be initlized in mem_cgroup_prepare_migration().
> > > I'll send patch later.
> > >
> > I see, thanks.
> >
> > I think you know it, but just a note:
> > mem_cgroup_{try_charge|commit_charge}_swapin()
> > use the same logic, so try_charge_swapin() should also be changed
> > for consistency.
> >
>
> Thank you for caution. But I think THP+memcg bugs should be fixed before
> style fixes..
>
I do agree.
> After my patch (yesterday), accounting information seems works well but
> I saw very huge latency when we hit limits.
> ==
> Jan 18 10:27:22 rhel6-test kernel: [56177.770922] sh used greatest stack depth: 3592 bytes l
> eft
> Jan 18 10:28:29 rhel6-test kernel: [56245.286007] INFO: rcu_sched_state detected stall on CP
> U 0 (t=60000 jiffies)
> Jan 18 10:28:29 rhel6-test kernel: [56245.286007] sending NMI to all CPUs:
> ...
> Jan 18 10:28:29 rhel6-test kernel: [56245.286007] NMI backtrace for cpu 0
> Jan 18 10:28:29 rhel6-test kernel: [56245.286007] CPU 0
> Jan 18 10:28:29 rhel6-test kernel: [56245.286007] Modules linked in: autofs4 sunrpc ip6t_REJECT nf_conntrack_ipv6 nf_defrag_ipv6 ip6table_filter ip6_tables ipv6 virtio_balloon virtio_net virtio_blk virtio_pci virtio_ring virtio [last unloaded: scsi_wait_scan]
> Jan 18 10:28:29 rhel6-test kernel: [56245.286007]
> ...
> Jan 18 10:28:29 rhel6-test kernel: [56245.286007] <IRQ>
> Jan 18 10:28:29 rhel6-test kernel: [56245.286007] [<ffffffff8102a04e>] arch_trigger_all_cpu_backtrace+0x5e/0xa0
> Jan 18 10:28:29 rhel6-test kernel: [56245.286007] [<ffffffff810bca09>] __rcu_pending+0x169/0x3b0
> Jan 18 10:28:29 rhel6-test kernel: [56245.286007] [<ffffffff8108a250>] ? tick_sched_timer+0x0/0xc0
> Jan 18 10:28:29 rhel6-test kernel: [56245.286007] [<ffffffff810bccbc>] rcu_check_callbacks+0x6c/0x120
> Jan 18 10:28:29 rhel6-test kernel: [56245.286007] [<ffffffff810689a8>] update_process_times+0x48/0x90
> Jan 18 10:28:29 rhel6-test kernel: [56245.286007] [<ffffffff8108a2b6>] tick_sched_timer+0x66/0xc0
> Jan 18 10:28:29 rhel6-test kernel: [56245.286007] [<ffffffff8107ede0>] __run_hrtimer+0x90/0x1e0
> Jan 18 10:28:29 rhel6-test kernel: [56245.286007] [<ffffffff81032db9>] ? kvm_clock_get_cycles+0x9/0x10
> Jan 18 10:28:29 rhel6-test kernel: [56245.286007] [<ffffffff8107f1be>] hrtimer_interrupt+0xde/0x240
> Jan 18 10:28:29 rhel6-test kernel: [56245.286007] [<ffffffff8155268b>] smp_apic_timer_interrupt+0x6b/0x9b
> Jan 18 10:28:29 rhel6-test kernel: [56245.286007] [<ffffffff8100c9d3>] apic_timer_interrupt+0x13/0x20
> Jan 18 10:28:29 rhel6-test kernel: [56245.286007] <EOI>
> Jan 18 10:28:29 rhel6-test kernel: [56245.286007] [<ffffffff810a726a>] ? res_counter_charge+0xda/0x100
> Jan 18 10:28:29 rhel6-test kernel: [56245.286007] [<ffffffff81145459>] __mem_cgroup_try_charge+0x199/0x5d0
> Jan 18 10:28:29 rhel6-test kernel: [56245.286007] [<ffffffff811461c6>] mem_cgroup_charge_common+0x96/0x110
> Jan 18 10:28:29 rhel6-test kernel: [56245.286007] [<ffffffff811463b5>] mem_cgroup_newpage_charge+0x45/0x50
> Jan 18 10:28:29 rhel6-test kernel: [56245.286007] [<ffffffff8113dbd4>] khugepaged+0x924/0x1430
> ==
>
> I guess we need to relax retry logic when page_size > PAGE_SIZE.
> I need to stop test application with Ctrl-C.
> (Test was make -j 16 under 200M limit.)
>
I think this is caused by a following scenario.
1. mem_cgroup_charge_common() try to charge a huge page(i.e. page_size != PAGE_SIZE).
2. mem_cgroup_do_charge() fails to charge, and return CHARGE_RETRY, because
"csize > PAGE_SIZE".
3. When mem_cgroup_do_charge() returns CHARGE_RETRY, mem_cgroup_charge_common()
changes 'csize' to 'page_size', which is bigger than PAGE_SIZE.
I think you're stuck inside a loop between 2 and 3.
Thanks,
Daisuke Nishimura.
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