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

On Wed, 19 Jan 2011 10:11:12 +0900
nishimura@mxp.nes.nec.co.jp wrote:

quoted

On Wed, 19 Jan 2011 09:27:33 +0900
Daisuke Nishimura [off-list ref] wrote:

quoted

On Tue, 18 Jan 2011 15:28:44 -0800
Andrew Morton [off-list ref] wrote:

quoted

On Tue, 18 Jan 2011 12:18:11 +0100
Miklos Szeredi [off-list ref] wrote:

quoted

+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..

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.)



Thanks,
-Kame


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