Re: [PATCH v4] mm: add replace_page_cache_page() function

[Daisuke Nishimura]

On Wed, 19 Jan 2011 10:23:48 +0900
KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> wrote:

> On Wed, 19 Jan 2011 10:11:12 +0900
> nishimura@xxxxxxxxxxxxxxxxx wrote:
> 
> > > On Wed, 19 Jan 2011 09:27:33 +0900
> > > Daisuke Nishimura <nishimura@xxxxxxxxxxxxxxxxx> wrote:
> > > 
> > >> On Tue, 18 Jan 2011 15:28:44 -0800
> > >> Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
> > >> 
> > >> > On Tue, 18 Jan 2011 12:18:11 +0100
> > >> > Miklos Szeredi <miklos@xxxxxxxxxx> 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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