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Re: [PATCH 04/31] mm, vmscan: begin reclaiming pages on a per-node basis

Started byJoonsoo Kim <iamjoonsoo.kim@lge.com>
First post2016-07-14 08:30 +0200
Last post2016-07-19 16:30 +0200
Articles 7 — 3 participants

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  Re: [PATCH 04/31] mm, vmscan: begin reclaiming pages on a per-node  basis Joonsoo Kim <iamjoonsoo.kim@lge.com> - 2016-07-14 08:30 +0200
    Re: [PATCH 04/31] mm, vmscan: begin reclaiming pages on a per-node  basis Vlastimil Babka <vbabka@suse.cz> - 2016-07-14 09:50 +0200
      Re: [PATCH 04/31] mm, vmscan: begin reclaiming pages on a per-node  basis Joonsoo Kim <iamjoonsoo.kim@lge.com> - 2016-07-18 06:50 +0200
    Re: [PATCH 04/31] mm, vmscan: begin reclaiming pages on a per-node  basis Mel Gorman <mgorman@techsingularity.net> - 2016-07-18 14:20 +0200
      Re: [PATCH 04/31] mm, vmscan: begin reclaiming pages on a per-node  basis Mel Gorman <mgorman@techsingularity.net> - 2016-07-18 16:30 +0200
        Re: [PATCH 04/31] mm, vmscan: begin reclaiming pages on a per-node  basis Joonsoo Kim <iamjoonsoo.kim@lge.com> - 2016-07-19 10:30 +0200
          Re: [PATCH 04/31] mm, vmscan: begin reclaiming pages on a per-node  basis Mel Gorman <mgorman@techsingularity.net> - 2016-07-19 16:30 +0200

#1443098 — Re: [PATCH 04/31] mm, vmscan: begin reclaiming pages on a per-node basis

FromJoonsoo Kim <iamjoonsoo.kim@lge.com>
Date2016-07-14 08:30 +0200
SubjectRe: [PATCH 04/31] mm, vmscan: begin reclaiming pages on a per-node basis
Message-ID<rUIjL-5Tv-1@gated-at.bofh.it>
On Fri, Jul 08, 2016 at 11:05:32AM +0100, Mel Gorman wrote:
> On Fri, Jul 08, 2016 at 11:28:52AM +0900, Joonsoo Kim wrote:
> > On Thu, Jul 07, 2016 at 10:48:08AM +0100, Mel Gorman wrote:
> > > On Thu, Jul 07, 2016 at 10:12:12AM +0900, Joonsoo Kim wrote:
> > > > > @@ -1402,6 +1406,11 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
> > > > >  
> > > > >  		VM_BUG_ON_PAGE(!PageLRU(page), page);
> > > > >  
> > > > > +		if (page_zonenum(page) > sc->reclaim_idx) {
> > > > > +			list_move(&page->lru, &pages_skipped);
> > > > > +			continue;
> > > > > +		}
> > > > > +
> > > > 
> > > > I think that we don't need to skip LRU pages in active list. What we'd
> > > > like to do is just skipping actual reclaim since it doesn't make
> > > > freepage that we need. It's unrelated to skip the page in active list.
> > > > 
> > > 
> > > Why?
> > > 
> > > The active aging is sometimes about simply aging the LRU list. Aging the
> > > active list based on the timing of when a zone-constrained allocation arrives
> > > potentially introduces the same zone-balancing problems we currently have
> > > and applying them to node-lru.
> > 
> > Could you explain more? I don't understand why aging the active list
> > based on the timing of when a zone-constrained allocation arrives
> > introduces the zone-balancing problem again.
> > 
> 
> I mispoke. Avoid rotation of the active list based on the timing of a
> zone-constrained allocation is what I think potentially introduces problems.
> If there are zone-constrained allocations aging the active list then I worry
> that pages would be artificially preserved on the active list.  No matter
> what we do, there is distortion of the aging for zone-constrained allocation
> because right now, it may deactivate high zone pages sooner than expected.
> 
> > I think that if above logic is applied to both the active/inactive
> > list, it could cause zone-balancing problem. LRU pages on lower zone
> > can be resident on memory with more chance.
> 
> If anything, with node-based LRU, it's high zone pages that can be resident
> on memory for longer but only if there are zone-constrained allocations.
> If we always reclaim based on age regardless of allocation requirements
> then there is a risk that high zones are reclaimed far earlier than expected.
> 
> Basically, whether we skip pages in the active list or not there are
> distortions with page aging and the impact is workload dependent. Right now,
> I see no clear advantage to special casing active aging.
> 
> If we suspect this is a problem in the future, it would be a simple matter
> of adding an additional bool parameter to isolate_lru_pages.

Okay. I agree that it would be a simple matter.

> 
> > > > And, I have a concern that if inactive LRU is full with higher zone's
> > > > LRU pages, reclaim with low reclaim_idx could be stuck.
> > > 
> > > That is an outside possibility but unlikely given that it would require
> > > that all outstanding allocation requests are zone-contrained. If it happens
> > 
> > I'm not sure that it is outside possibility. It can also happens if there
> > is zone-contrained allocation requestor and parallel memory hogger. In
> > this case, memory would be reclaimed by memory hogger but memory hogger would
> > consume them again so inactive LRU is continually full with higher
> > zone's LRU pages and zone-contrained allocation requestor cannot
> > progress.
> > 
> 
> The same memory hogger will also be reclaiming the highmem pages and
> reallocating highmem pages.
> 
> > > It would be preferred to have an actual test case for this so the
> > > altered ratio can be tested instead of introducing code that may be
> > > useless or dead.
> > 
> > Yes, actual test case would be preferred. I will try to implement
> > an artificial test case by myself but I'm not sure when I can do it.
> > 
> 
> That would be appreciated.

I make an artificial test case and test this series by using next tree
(next-20160713) and found a regression.

My test setup is:

memory: 2048 mb
movablecore: 1500 mb (imitates highmem system to test effect of skip logic)
swapoff
forever repeat: sequential read file (1500 mb) (using mmap) by 2 threads
3000 processes fork

lowmem is roughly 500 mb and it is enough to keep 3000 processes. I
test this artificial scenario with v4.7-rc5 and find no problem. But,
with next-20160713, OOM kill is triggered as below.


-------- oops -------

fork invoked oom-killer: gfp_mask=0x27000c0(GFP_KERNEL_ACCOUNT|__GFP_NOTRACK), order=2, oom_score_adj=0
fork cpuset=/ mems_allowed=0
CPU: 0 PID: 10478 Comm: fork Not tainted 4.7.0-rc7-next-20160713 #646
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.9.1-0-gb3ef39f-prebuilt.qemu-project.org 04/01/2014
 0000000000000000 ffff880014273b18 ffffffff8142b8c3 ffff880014273d20
 ffff88001c44a500 ffff880014273b90 ffffffff81240b6e ffffffff81e6f0e0
 ffff880014273b40 ffffffff810de08d ffff880014273b60 0000000000000206
Call Trace:
 [<ffffffff8142b8c3>] dump_stack+0x85/0xc2
 [<ffffffff81240b6e>] dump_header+0x5c/0x22e
 [<ffffffff810de08d>] ? trace_hardirqs_on+0xd/0x10
 [<ffffffff811b3381>] oom_kill_process+0x221/0x3f0
 [<ffffffff810901b7>] ? has_capability_noaudit+0x17/0x20
 [<ffffffff811b3acf>] out_of_memory+0x52f/0x560
 [<ffffffff811b377c>] ? out_of_memory+0x1dc/0x560
 [<ffffffff811ba004>] __alloc_pages_nodemask+0x1154/0x11b0
 [<ffffffff810813a1>] ? copy_process.part.30+0x121/0x1bf0
 [<ffffffff810813a1>] copy_process.part.30+0x121/0x1bf0
 [<ffffffff811ebb06>] ? handle_mm_fault+0xb36/0x13d0
 [<ffffffff810fb60d>] ? debug_lockdep_rcu_enabled+0x1d/0x20
 [<ffffffff81083066>] _do_fork+0xe6/0x6a0
 [<ffffffff810836c9>] SyS_clone+0x19/0x20
 [<ffffffff81003e13>] do_syscall_64+0x73/0x1e0
 [<ffffffff81858ec3>] entry_SYSCALL64_slow_path+0x25/0x25
Mem-Info:
active_anon:19756 inactive_anon:18 isolated_anon:0
 active_file:142480 inactive_file:266065 isolated_file:0
 unevictable:0 dirty:0 writeback:0 unstable:0
 slab_reclaimable:6777 slab_unreclaimable:19127
 mapped:389778 shmem:95 pagetables:17512 bounce:0
 free:9533 free_pcp:80 free_cma:0
Node 0 active_anon:79024kB inactive_anon:72kB active_file:569920kB inactive_file:1064260kB unevictable:0kB isolated(anon):0kB isolated(file):0kB mapped:1559112kB dirty:0kB writeback:0kB shmem:0kB shmem_thp
: 0kB shmem_pmdmapped: 0kB anon_thp: 380kB writeback_tmp:0kB unstable:0kB all_unreclaimable? yes
Node 0 DMA free:2172kB min:204kB low:252kB high:300kB present:15992kB managed:15908kB mlocked:0kB slab_reclaimable:0kB slab_unreclaimable:2272kB kernel_stack:1216kB pagetables:2436kB bounce:0kB free_pcp:0k
B local_pcp:0kB free_cma:0kB node_pages_scanned:15639736
lowmem_reserve[]: 0 493 493 1955
Node 0 DMA32 free:6372kB min:6492kB low:8112kB high:9732kB present:2080632kB managed:508600kB mlocked:0kB slab_reclaimable:27108kB slab_unreclaimable:74236kB kernel_stack:32752kB pagetables:67612kB bounce:
0kB free_pcp:112kB local_pcp:12kB free_cma:0kB node_pages_scanned:16302012
lowmem_reserve[]: 0 0 0 1462
Node 0 Normal free:0kB min:0kB low:0kB high:0kB present:18446744073708015752kB managed:0kB mlocked:0kB slab_reclaimable:0kB slab_unreclaimable:0kB kernel_stack:0kB pagetables:0kB bounce:0kB free_pcp:0kB lo
cal_pcp:0kB free_cma:0kB node_pages_scanned:17033632
lowmem_reserve[]: 0 0 0 11698
Node 0 Movable free:29588kB min:19256kB low:24068kB high:28880kB present:1535864kB managed:1500964kB mlocked:0kB slab_reclaimable:0kB slab_unreclaimable:0kB kernel_stack:0kB pagetables:0kB bounce:0kB free_
pcp:208kB local_pcp:112kB free_cma:0kB node_pages_scanned:17725436
lowmem_reserve[]: 0 0 0 0
Node 0 DMA: 1*4kB (M) 1*8kB (U) 1*16kB (M) 1*32kB (M) 1*64kB (M) 2*128kB (UM) 1*256kB (M) 1*512kB (U) 1*1024kB (U) 0*2048kB 0*4096kB = 2172kB
Node 0 DMA32: 60*4kB (ME) 45*8kB (UME) 24*16kB (ME) 13*32kB (UM) 12*64kB (UM) 6*128kB (UM) 6*256kB (M) 4*512kB (UM) 0*1024kB 0*2048kB 0*4096kB = 6520kB
Node 0 Normal: 0*4kB 0*8kB 0*16kB 0*32kB 0*64kB 0*128kB 0*256kB 0*512kB 0*1024kB 0*2048kB 0*4096kB = 0kB
Node 0 Movable: 1*4kB (M) 130*8kB (M) 68*16kB (M) 30*32kB (M) 13*64kB (M) 9*128kB (M) 4*256kB (M) 0*512kB 1*1024kB (M) 1*2048kB (M) 5*4096kB (M) = 29652kB
Node 0 hugepages_total=0 hugepages_free=0 hugepages_surp=0 hugepages_size=2048kB
408717 total pagecache pages
0 pages in swap cache
Swap cache stats: add 0, delete 0, find 0/0
Free swap  = 0kB
Total swap = 0kB
524156 pages RAM
0 pages HighMem/MovableOnly
17788 pages reserved
0 pages cma reserved
0 pages hwpoisoned



-------- another one -------

fork invoked oom-killer: gfp_mask=0x25080c0(GFP_KERNEL_ACCOUNT|__GFP_ZERO), order=0, oom_score_adj=0
fork cpuset=/ mems_allowed=0
CPU: 3 PID: 7538 Comm: fork Not tainted 4.7.0-rc7-next-20160713 #646
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.9.1-0-gb3ef39f-prebuilt.qemu-project.org 04/01/2014
 0000000000000000 ffff8800141eb960 ffffffff8142b8c3 ffff8800141ebb68
 ffff88001c46a500 ffff8800141eb9d8 ffffffff81240b6e ffffffff81e6f0e0
 ffff8800141eb988 ffffffff810de08d ffff8800141eb9a8 0000000000000206
Call Trace:
 [<ffffffff8142b8c3>] dump_stack+0x85/0xc2
 [<ffffffff81240b6e>] dump_header+0x5c/0x22e
 [<ffffffff810de08d>] ? trace_hardirqs_on+0xd/0x10
 [<ffffffff811b3381>] oom_kill_process+0x221/0x3f0
 [<ffffffff810901b7>] ? has_capability_noaudit+0x17/0x20
 [<ffffffff811b3acf>] out_of_memory+0x52f/0x560
 [<ffffffff811b377c>] ? out_of_memory+0x1dc/0x560
 [<ffffffff811ba004>] __alloc_pages_nodemask+0x1154/0x11b0
 [<ffffffff8120ed61>] ? alloc_pages_current+0xa1/0x1f0
 [<ffffffff8120ed61>] alloc_pages_current+0xa1/0x1f0
 [<ffffffff811eae37>] ? __pmd_alloc+0x37/0x1d0
 [<ffffffff811eae37>] __pmd_alloc+0x37/0x1d0
 [<ffffffff811ed627>] copy_page_range+0x947/0xa50
 [<ffffffff811f9386>] ? anon_vma_fork+0xd6/0x150
 [<ffffffff81432bd2>] ? __rb_insert_augmented+0x132/0x210
 [<ffffffff81082035>] copy_process.part.30+0xdb5/0x1bf0
 [<ffffffff81083066>] _do_fork+0xe6/0x6a0
 [<ffffffff810836c9>] SyS_clone+0x19/0x20
 [<ffffffff81003e13>] do_syscall_64+0x73/0x1e0
 [<ffffffff81858ec3>] entry_SYSCALL64_slow_path+0x25/0x25
Mem-Info:
active_anon:18779 inactive_anon:18 isolated_anon:0
 active_file:91577 inactive_file:320615 isolated_file:0
 unevictable:0 dirty:0 writeback:0 unstable:0
 slab_reclaimable:6741 slab_unreclaimable:18124
 mapped:389774 shmem:95 pagetables:18332 bounce:0
 free:8194 free_pcp:140 free_cma:0
Node 0 active_anon:75116kB inactive_anon:72kB active_file:366308kB inactive_file:1282460kB unevictable:0kB isolated(anon):0kB isolated(file):0kB mapped:1559096kB dirty:0kB writeback:0kB shmem:0kB shmem_thp: 0kB shmem_pmdmapped: 0kB anon_thp: 380kB writeback_tmp:0kB unstable:0kB all_unreclaimable? yes
Node 0 DMA free:2172kB min:204kB low:252kB high:300kB present:15992kB managed:15908kB mlocked:0kB slab_reclaimable:0kB slab_unreclaimable:2380kB kernel_stack:1632kB pagetables:3632kB bounce:0kB free_pcp:0kB local_pcp:0kB free_cma:0kB node_pages_scanned:13673372
lowmem_reserve[]: 0 493 493 1955
Node 0 DMA32 free:6444kB min:6492kB low:8112kB high:9732kB present:2080632kB managed:508600kB mlocked:0kB slab_reclaimable:26964kB slab_unreclaimable:70116kB kernel_stack:30496kB pagetables:69696kB bounce:0kB free_pcp:316kB local_pcp:100kB free_cma:0kB node_pages_scanned:13673372
lowmem_reserve[]: 0 0 0 1462
Node 0 Normal free:0kB min:0kB low:0kB high:0kB present:18446744073708015752kB managed:0kB mlocked:0kB slab_reclaimable:0kB slab_unreclaimable:0kB kernel_stack:0kB pagetables:0kB bounce:0kB free_pcp:0kB local_pcp:0kB free_cma:0kB node_pages_scanned:13673832
lowmem_reserve[]: 0 0 0 11698
Node 0 Movable free:24200kB min:19256kB low:24068kB high:28880kB present:1535864kB managed:1500964kB mlocked:0kB slab_reclaimable:0kB slab_unreclaimable:0kB kernel_stack:0kB pagetables:0kB bounce:0kB free_pcp:956kB local_pcp:100kB free_cma:0kB node_pages_scanned:1504
lowmem_reserve[]: 0 0 0 0
Node 0 DMA: 2*4kB (M) 0*8kB 1*16kB (M) 0*32kB 1*64kB (M) 0*128kB 2*256kB (UM) 1*512kB (M) 1*1024kB (U) 0*2048kB 0*4096kB = 2136kB
Node 0 DMA32: 58*4kB (ME) 40*8kB (UME) 27*16kB (UME) 15*32kB (ME) 8*64kB (UM) 5*128kB (M) 10*256kB (UM) 1*512kB (U) 1*1024kB (M) 0*2048kB 0*4096kB = 6712kB
Node 0 Normal: 0*4kB 0*8kB 0*16kB 0*32kB 0*64kB 0*128kB 0*256kB 0*512kB 0*1024kB 0*2048kB 0*4096kB = 0kB
Node 0 Movable: 40*4kB (M) 8*8kB (M) 3*16kB (M) 6*32kB (M) 7*64kB (M) 2*128kB (M) 1*256kB (M) 2*512kB (M) 2*1024kB (M) 1*2048kB (M) 5*4096kB (M) = 27024kB
Node 0 hugepages_total=0 hugepages_free=0 hugepages_surp=0 hugepages_size=2048kB
411446 total pagecache pages
0 pages in swap cache
Swap cache stats: add 0, delete 0, find 0/0
Free swap  = 0kB
Total swap = 0kB
524156 pages RAM
0 pages HighMem/MovableOnly
17788 pages reserved
0 pages cma reserved

Size of active/inactive_file is larger than size of movable zone so I guess
there is reclaimable pages on DMA32 and it would mean that there is some problems
related to skip logic. Could you help how to check it?

Thanks.

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#1443142

FromVlastimil Babka <vbabka@suse.cz>
Date2016-07-14 09:50 +0200
Message-ID<rUJzb-6C2-9@gated-at.bofh.it>
In reply to#1443098
On 07/14/2016 08:28 AM, Joonsoo Kim wrote:
> On Fri, Jul 08, 2016 at 11:05:32AM +0100, Mel Gorman wrote:
>> On Fri, Jul 08, 2016 at 11:28:52AM +0900, Joonsoo Kim wrote:
>>> On Thu, Jul 07, 2016 at 10:48:08AM +0100, Mel Gorman wrote:
>>>> On Thu, Jul 07, 2016 at 10:12:12AM +0900, Joonsoo Kim wrote:
>>>>>> @@ -1402,6 +1406,11 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
>>>>>>
>>>>>>  		VM_BUG_ON_PAGE(!PageLRU(page), page);
>>>>>>
>>>>>> +		if (page_zonenum(page) > sc->reclaim_idx) {
>>>>>> +			list_move(&page->lru, &pages_skipped);
>>>>>> +			continue;
>>>>>> +		}
>>>>>> +
>>>>>
>>>>> I think that we don't need to skip LRU pages in active list. What we'd
>>>>> like to do is just skipping actual reclaim since it doesn't make
>>>>> freepage that we need. It's unrelated to skip the page in active list.
>>>>>
>>>>
>>>> Why?
>>>>
>>>> The active aging is sometimes about simply aging the LRU list. Aging the
>>>> active list based on the timing of when a zone-constrained allocation arrives
>>>> potentially introduces the same zone-balancing problems we currently have
>>>> and applying them to node-lru.
>>>
>>> Could you explain more? I don't understand why aging the active list
>>> based on the timing of when a zone-constrained allocation arrives
>>> introduces the zone-balancing problem again.
>>>
>>
>> I mispoke. Avoid rotation of the active list based on the timing of a
>> zone-constrained allocation is what I think potentially introduces problems.
>> If there are zone-constrained allocations aging the active list then I worry
>> that pages would be artificially preserved on the active list.  No matter
>> what we do, there is distortion of the aging for zone-constrained allocation
>> because right now, it may deactivate high zone pages sooner than expected.
>>
>>> I think that if above logic is applied to both the active/inactive
>>> list, it could cause zone-balancing problem. LRU pages on lower zone
>>> can be resident on memory with more chance.
>>
>> If anything, with node-based LRU, it's high zone pages that can be resident
>> on memory for longer but only if there are zone-constrained allocations.
>> If we always reclaim based on age regardless of allocation requirements
>> then there is a risk that high zones are reclaimed far earlier than expected.
>>
>> Basically, whether we skip pages in the active list or not there are
>> distortions with page aging and the impact is workload dependent. Right now,
>> I see no clear advantage to special casing active aging.
>>
>> If we suspect this is a problem in the future, it would be a simple matter
>> of adding an additional bool parameter to isolate_lru_pages.
>
> Okay. I agree that it would be a simple matter.
>
>>
>>>>> And, I have a concern that if inactive LRU is full with higher zone's
>>>>> LRU pages, reclaim with low reclaim_idx could be stuck.
>>>>
>>>> That is an outside possibility but unlikely given that it would require
>>>> that all outstanding allocation requests are zone-contrained. If it happens
>>>
>>> I'm not sure that it is outside possibility. It can also happens if there
>>> is zone-contrained allocation requestor and parallel memory hogger. In
>>> this case, memory would be reclaimed by memory hogger but memory hogger would
>>> consume them again so inactive LRU is continually full with higher
>>> zone's LRU pages and zone-contrained allocation requestor cannot
>>> progress.
>>>
>>
>> The same memory hogger will also be reclaiming the highmem pages and
>> reallocating highmem pages.
>>
>>>> It would be preferred to have an actual test case for this so the
>>>> altered ratio can be tested instead of introducing code that may be
>>>> useless or dead.
>>>
>>> Yes, actual test case would be preferred. I will try to implement
>>> an artificial test case by myself but I'm not sure when I can do it.
>>>
>>
>> That would be appreciated.
>
> I make an artificial test case and test this series by using next tree
> (next-20160713) and found a regression.
>

[...]

> Mem-Info:
> active_anon:18779 inactive_anon:18 isolated_anon:0
>  active_file:91577 inactive_file:320615 isolated_file:0
>  unevictable:0 dirty:0 writeback:0 unstable:0
>  slab_reclaimable:6741 slab_unreclaimable:18124
>  mapped:389774 shmem:95 pagetables:18332 bounce:0
>  free:8194 free_pcp:140 free_cma:0
> Node 0 active_anon:75116kB inactive_anon:72kB active_file:366308kB inactive_file:1282460kB unevictable:0kB isolated(anon):0kB isolated(file):0kB mapped:1559096kB dirty:0kB writeback:0kB shmem:0kB shmem_thp: 0kB shmem_pmdmapped: 0kB anon_thp: 380kB writeback_tmp:0kB unstable:0kB all_unreclaimable? yes
> Node 0 DMA free:2172kB min:204kB low:252kB high:300kB present:15992kB managed:15908kB mlocked:0kB slab_reclaimable:0kB slab_unreclaimable:2380kB kernel_stack:1632kB pagetables:3632kB bounce:0kB free_pcp:0kB local_pcp:0kB free_cma:0kB node_pages_scanned:13673372
> lowmem_reserve[]: 0 493 493 1955
> Node 0 DMA32 free:6444kB min:6492kB low:8112kB high:9732kB present:2080632kB managed:508600kB mlocked:0kB slab_reclaimable:26964kB slab_unreclaimable:70116kB kernel_stack:30496kB pagetables:69696kB bounce:0kB free_pcp:316kB local_pcp:100kB free_cma:0kB node_pages_scanned:13673372
> lowmem_reserve[]: 0 0 0 1462
> Node 0 Normal free:0kB min:0kB low:0kB high:0kB present:18446744073708015752kB managed:0kB mlocked:0kB slab_reclaimable:0kB slab_unreclaimable:0kB kernel_stack:0kB pagetables:0kB bounce:0kB free_pcp:0kB local_pcp:0kB free_cma:0kB node_pages_scanned:13673832

present:18446744073708015752kB

Although unlikely related to your report, that itself doesn't look 
right. Any idea if that's due to your configuration and would be printed 
also in the mainline kernel in case of OOM (or if /proc/zoneinfo has 
similarly bogus value), or is something caused by a patch in mmotm?

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#1445200

FromJoonsoo Kim <iamjoonsoo.kim@lge.com>
Date2016-07-18 06:50 +0200
Message-ID<rW8Fb-1zz-3@gated-at.bofh.it>
In reply to#1443142
On Thu, Jul 14, 2016 at 09:48:41AM +0200, Vlastimil Babka wrote:
> On 07/14/2016 08:28 AM, Joonsoo Kim wrote:
> >On Fri, Jul 08, 2016 at 11:05:32AM +0100, Mel Gorman wrote:
> >>On Fri, Jul 08, 2016 at 11:28:52AM +0900, Joonsoo Kim wrote:
> >>>On Thu, Jul 07, 2016 at 10:48:08AM +0100, Mel Gorman wrote:
> >>>>On Thu, Jul 07, 2016 at 10:12:12AM +0900, Joonsoo Kim wrote:
> >>>>>>@@ -1402,6 +1406,11 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
> >>>>>>
> >>>>>> 		VM_BUG_ON_PAGE(!PageLRU(page), page);
> >>>>>>
> >>>>>>+		if (page_zonenum(page) > sc->reclaim_idx) {
> >>>>>>+			list_move(&page->lru, &pages_skipped);
> >>>>>>+			continue;
> >>>>>>+		}
> >>>>>>+
> >>>>>
> >>>>>I think that we don't need to skip LRU pages in active list. What we'd
> >>>>>like to do is just skipping actual reclaim since it doesn't make
> >>>>>freepage that we need. It's unrelated to skip the page in active list.
> >>>>>
> >>>>
> >>>>Why?
> >>>>
> >>>>The active aging is sometimes about simply aging the LRU list. Aging the
> >>>>active list based on the timing of when a zone-constrained allocation arrives
> >>>>potentially introduces the same zone-balancing problems we currently have
> >>>>and applying them to node-lru.
> >>>
> >>>Could you explain more? I don't understand why aging the active list
> >>>based on the timing of when a zone-constrained allocation arrives
> >>>introduces the zone-balancing problem again.
> >>>
> >>
> >>I mispoke. Avoid rotation of the active list based on the timing of a
> >>zone-constrained allocation is what I think potentially introduces problems.
> >>If there are zone-constrained allocations aging the active list then I worry
> >>that pages would be artificially preserved on the active list.  No matter
> >>what we do, there is distortion of the aging for zone-constrained allocation
> >>because right now, it may deactivate high zone pages sooner than expected.
> >>
> >>>I think that if above logic is applied to both the active/inactive
> >>>list, it could cause zone-balancing problem. LRU pages on lower zone
> >>>can be resident on memory with more chance.
> >>
> >>If anything, with node-based LRU, it's high zone pages that can be resident
> >>on memory for longer but only if there are zone-constrained allocations.
> >>If we always reclaim based on age regardless of allocation requirements
> >>then there is a risk that high zones are reclaimed far earlier than expected.
> >>
> >>Basically, whether we skip pages in the active list or not there are
> >>distortions with page aging and the impact is workload dependent. Right now,
> >>I see no clear advantage to special casing active aging.
> >>
> >>If we suspect this is a problem in the future, it would be a simple matter
> >>of adding an additional bool parameter to isolate_lru_pages.
> >
> >Okay. I agree that it would be a simple matter.
> >
> >>
> >>>>>And, I have a concern that if inactive LRU is full with higher zone's
> >>>>>LRU pages, reclaim with low reclaim_idx could be stuck.
> >>>>
> >>>>That is an outside possibility but unlikely given that it would require
> >>>>that all outstanding allocation requests are zone-contrained. If it happens
> >>>
> >>>I'm not sure that it is outside possibility. It can also happens if there
> >>>is zone-contrained allocation requestor and parallel memory hogger. In
> >>>this case, memory would be reclaimed by memory hogger but memory hogger would
> >>>consume them again so inactive LRU is continually full with higher
> >>>zone's LRU pages and zone-contrained allocation requestor cannot
> >>>progress.
> >>>
> >>
> >>The same memory hogger will also be reclaiming the highmem pages and
> >>reallocating highmem pages.
> >>
> >>>>It would be preferred to have an actual test case for this so the
> >>>>altered ratio can be tested instead of introducing code that may be
> >>>>useless or dead.
> >>>
> >>>Yes, actual test case would be preferred. I will try to implement
> >>>an artificial test case by myself but I'm not sure when I can do it.
> >>>
> >>
> >>That would be appreciated.
> >
> >I make an artificial test case and test this series by using next tree
> >(next-20160713) and found a regression.
> >
> 
> [...]
> 
> >Mem-Info:
> >active_anon:18779 inactive_anon:18 isolated_anon:0
> > active_file:91577 inactive_file:320615 isolated_file:0
> > unevictable:0 dirty:0 writeback:0 unstable:0
> > slab_reclaimable:6741 slab_unreclaimable:18124
> > mapped:389774 shmem:95 pagetables:18332 bounce:0
> > free:8194 free_pcp:140 free_cma:0
> >Node 0 active_anon:75116kB inactive_anon:72kB active_file:366308kB inactive_file:1282460kB unevictable:0kB isolated(anon):0kB isolated(file):0kB mapped:1559096kB dirty:0kB writeback:0kB shmem:0kB shmem_thp: 0kB shmem_pmdmapped: 0kB anon_thp: 380kB writeback_tmp:0kB unstable:0kB all_unreclaimable? yes
> >Node 0 DMA free:2172kB min:204kB low:252kB high:300kB present:15992kB managed:15908kB mlocked:0kB slab_reclaimable:0kB slab_unreclaimable:2380kB kernel_stack:1632kB pagetables:3632kB bounce:0kB free_pcp:0kB local_pcp:0kB free_cma:0kB node_pages_scanned:13673372
> >lowmem_reserve[]: 0 493 493 1955
> >Node 0 DMA32 free:6444kB min:6492kB low:8112kB high:9732kB present:2080632kB managed:508600kB mlocked:0kB slab_reclaimable:26964kB slab_unreclaimable:70116kB kernel_stack:30496kB pagetables:69696kB bounce:0kB free_pcp:316kB local_pcp:100kB free_cma:0kB node_pages_scanned:13673372
> >lowmem_reserve[]: 0 0 0 1462
> >Node 0 Normal free:0kB min:0kB low:0kB high:0kB present:18446744073708015752kB managed:0kB mlocked:0kB slab_reclaimable:0kB slab_unreclaimable:0kB kernel_stack:0kB pagetables:0kB bounce:0kB free_pcp:0kB local_pcp:0kB free_cma:0kB node_pages_scanned:13673832
> 
> present:18446744073708015752kB
> 
> Although unlikely related to your report, that itself doesn't look
> right. Any idea if that's due to your configuration and would be
> printed also in the mainline kernel in case of OOM (or if
> /proc/zoneinfo has similarly bogus value), or is something caused by
> a patch in mmotm?

Wrong present count is due to a bug when enabling MOVABLE_ZONE.
v4.7-rc5 also has the same problems.

I testes above tests with work-around of this present count bug and
find that result is the same. v4.7-rc5 is okay but next-20160713 isn't okay.

As I said before, this setup just imitate highmem system and problem
would also exist on highmem system.

In addition, on above setup, I measured hackbench performance while
there is a concurrent file reader and found that hackbench slow down
roughly 10% with nodelru.

Thanks.

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#1445424

FromMel Gorman <mgorman@techsingularity.net>
Date2016-07-18 14:20 +0200
Message-ID<rWfGF-62e-7@gated-at.bofh.it>
In reply to#1443098
On Thu, Jul 14, 2016 at 03:28:37PM +0900, Joonsoo Kim wrote:
> > That would be appreciated.
> 
> I make an artificial test case and test this series by using next tree
> (next-20160713) and found a regression.
> 
> My test setup is:
> 
> memory: 2048 mb
> movablecore: 1500 mb (imitates highmem system to test effect of skip logic)

This is not an equivalent test to highmem. Movable cannot store page table
pages and the highmem:lowmem ratio with this configuration is higher than
it should be. The OOM is still odd but the differences are worth
highlighting.

> fork invoked oom-killer: gfp_mask=0x27000c0(GFP_KERNEL_ACCOUNT|__GFP_NOTRACK), order=2, oom_score_adj=0
> fork cpuset=/ mems_allowed=0

Ok, high-order allocation failure for an allocation request that can
enter direct reclaim.

> Node 0 active_anon:79024kB inactive_anon:72kB active_file:569920kB inactive_file:1064260kB unevictable:0kB isolated(anon):0kB isolated(file):0kB mapped:1559112kB dirty:0kB writeback:0kB shmem:0kB shmem_thp
> : 0kB shmem_pmdmapped: 0kB anon_thp: 380kB writeback_tmp:0kB unstable:0kB all_unreclaimable? yes
> Node 0 DMA free:2172kB min:204kB low:252kB high:300kB present:15992kB managed:15908kB mlocked:0kB slab_reclaimable:0kB slab_unreclaimable:2272kB kernel_stack:1216kB pagetables:2436kB bounce:0kB free_pcp:0k
> B local_pcp:0kB free_cma:0kB node_pages_scanned:15639736
> lowmem_reserve[]: 0 493 493 1955
> Node 0 DMA32 free:6372kB min:6492kB low:8112kB high:9732kB present:2080632kB managed:508600kB mlocked:0kB slab_reclaimable:27108kB slab_unreclaimable:74236kB kernel_stack:32752kB pagetables:67612kB bounce:
> 0kB free_pcp:112kB local_pcp:12kB free_cma:0kB node_pages_scanned:16302012
> lowmem_reserve[]: 0 0 0 1462
> Node 0 Normal free:0kB min:0kB low:0kB high:0kB present:18446744073708015752kB managed:0kB mlocked:0kB slab_reclaimable:0kB slab_unreclaimable:0kB kernel_stack:0kB pagetables:0kB bounce:0kB free_pcp:0kB lo
> cal_pcp:0kB free_cma:0kB node_pages_scanned:17033632
> lowmem_reserve[]: 0 0 0 11698
> Node 0 Movable free:29588kB min:19256kB low:24068kB high:28880kB present:1535864kB managed:1500964kB mlocked:0kB slab_reclaimable:0kB slab_unreclaimable:0kB kernel_stack:0kB pagetables:0kB bounce:0kB free_
> pcp:208kB local_pcp:112kB free_cma:0kB node_pages_scanned:17725436

Present is corrupt but it's also interesting to note that
all_unreclaimable is true.

> lowmem_reserve[]: 0 0 0 0
> Node 0 DMA: 1*4kB (M) 1*8kB (U) 1*16kB (M) 1*32kB (M) 1*64kB (M) 2*128kB (UM) 1*256kB (M) 1*512kB (U) 1*1024kB (U) 0*2048kB 0*4096kB = 2172kB
> Node 0 DMA32: 60*4kB (ME) 45*8kB (UME) 24*16kB (ME) 13*32kB (UM) 12*64kB (UM) 6*128kB (UM) 6*256kB (M) 4*512kB (UM) 0*1024kB 0*2048kB 0*4096kB = 6520kB
> Node 0 Normal: 0*4kB 0*8kB 0*16kB 0*32kB 0*64kB 0*128kB 0*256kB 0*512kB 0*1024kB 0*2048kB 0*4096kB = 0kB
> Node 0 Movable: 1*4kB (M) 130*8kB (M) 68*16kB (M) 30*32kB (M) 13*64kB (M) 9*128kB (M) 4*256kB (M) 0*512kB 1*1024kB (M) 1*2048kB (M) 5*4096kB (M) = 29652kB
> Node 0 hugepages_total=0 hugepages_free=0 hugepages_surp=0 hugepages_size=2048kB

And it's true even though enough free pages are actually free so it's
not even trying to do the allocation.

The all_unreclaimable logic is related to the number of pages scanned
but currently pages skipped contributes to pages scanned. That is one
possibility. The other is that if all pages scanned are skipped then the
OOM killer can believe there is zero progress.

Try this to start with;

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 3f06a7a0d135..c3e509c693bf 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1408,7 +1408,7 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
 		isolate_mode_t mode, enum lru_list lru)
 {
 	struct list_head *src = &lruvec->lists[lru];
-	unsigned long nr_taken = 0;
+	unsigned long nr_taken = 0, total_skipped = 0;
 	unsigned long nr_zone_taken[MAX_NR_ZONES] = { 0 };
 	unsigned long nr_skipped[MAX_NR_ZONES] = { 0, };
 	unsigned long scan, nr_pages;
@@ -1462,10 +1462,11 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
 			if (!nr_skipped[zid])
 				continue;
 
+			total_skipped += nr_skipped[zid];
 			__count_zid_vm_events(PGSCAN_SKIP, zid, nr_skipped[zid]);
 		}
 	}
-	*nr_scanned = scan;
+	*nr_scanned = scan - total_skipped;
 	trace_mm_vmscan_lru_isolate(sc->reclaim_idx, sc->order, nr_to_scan, scan,
 				    nr_taken, mode, is_file_lru(lru));
 	update_lru_sizes(lruvec, lru, nr_zone_taken, nr_taken);

-- 
Mel Gorman
SUSE Labs

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#1445538

FromMel Gorman <mgorman@techsingularity.net>
Date2016-07-18 16:30 +0200
Message-ID<rWhIw-7l8-47@gated-at.bofh.it>
In reply to#1445424
On Mon, Jul 18, 2016 at 01:11:22PM +0100, Mel Gorman wrote:
> The all_unreclaimable logic is related to the number of pages scanned
> but currently pages skipped contributes to pages scanned. That is one
> possibility. The other is that if all pages scanned are skipped then the
> OOM killer can believe there is zero progress.
> 
> Try this to start with;
> 

And if that fails, try this heavier handed version that will scan the full
LRU potentially to isolate at least a single page if it's available for
zone-constrained allocations. It's compile-tested only

diff --git a/mm/vmscan.c b/mm/vmscan.c
index a6f31617a08c..6a35691c8b94 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1408,14 +1408,14 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
 		isolate_mode_t mode, enum lru_list lru)
 {
 	struct list_head *src = &lruvec->lists[lru];
-	unsigned long nr_taken = 0;
+	unsigned long nr_taken = 0, total_skipped = 0;
 	unsigned long nr_zone_taken[MAX_NR_ZONES] = { 0 };
 	unsigned long nr_skipped[MAX_NR_ZONES] = { 0, };
 	unsigned long scan, nr_pages;
 	LIST_HEAD(pages_skipped);
 
 	for (scan = 0; scan < nr_to_scan && nr_taken < nr_to_scan &&
-					!list_empty(src); scan++) {
+			!list_empty(src) && scan == total_skipped; scan++) {
 		struct page *page;
 
 		page = lru_to_page(src);
@@ -1426,6 +1426,7 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
 		if (page_zonenum(page) > sc->reclaim_idx) {
 			list_move(&page->lru, &pages_skipped);
 			nr_skipped[page_zonenum(page)]++;
+			total_skipped++;
 			continue;
 		}
 
@@ -1465,7 +1466,7 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
 			__count_zid_vm_events(PGSCAN_SKIP, zid, nr_skipped[zid]);
 		}
 	}
-	*nr_scanned = scan;
+	*nr_scanned = scan - total_skipped;
 	trace_mm_vmscan_lru_isolate(sc->reclaim_idx, sc->order, nr_to_scan, scan,
 				    nr_taken, mode, is_file_lru(lru));
 	update_lru_sizes(lruvec, lru, nr_zone_taken, nr_taken);

-- 
Mel Gorman
SUSE Labs

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#1446234

FromJoonsoo Kim <iamjoonsoo.kim@lge.com>
Date2016-07-19 10:30 +0200
Message-ID<rWyzE-1G2-5@gated-at.bofh.it>
In reply to#1445538
On Mon, Jul 18, 2016 at 03:27:14PM +0100, Mel Gorman wrote:
> On Mon, Jul 18, 2016 at 01:11:22PM +0100, Mel Gorman wrote:
> > The all_unreclaimable logic is related to the number of pages scanned
> > but currently pages skipped contributes to pages scanned. That is one
> > possibility. The other is that if all pages scanned are skipped then the
> > OOM killer can believe there is zero progress.
> > 
> > Try this to start with;
> > 
> 
> And if that fails, try this heavier handed version that will scan the full
> LRU potentially to isolate at least a single page if it's available for
> zone-constrained allocations. It's compile-tested only

I tested both patches but they don't work for me. Notable difference
is that all_unreclaimable is now "no".

Just attach the oops log from heavier version.

Thanks.

fork invoked oom-killer: gfp_mask=0x27000c0(GFP_KERNEL_ACCOUNT|__GFP_NOTRACK), order=2, oom_score_adj=0
fork cpuset=/ mems_allowed=0
CPU: 1 PID: 7484 Comm: fork Not tainted 4.7.0-rc7-next-20160713+ #657
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.9.1-0-gb3ef39f-prebuilt.qemu-project.org 04/01/2014
 0000000000000000 ffff880019f6bb18 ffffffff8142b8d3 ffff880019f6bd20
 ffff88001c2c2500 ffff880019f6bb90 ffffffff81240b7e ffffffff81e6f0e0
 ffff880019f6bb40 ffffffff810de08d ffff880019f6bb60 0000000000000206
Call Trace:
 [<ffffffff8142b8d3>] dump_stack+0x85/0xc2
 [<ffffffff81240b7e>] dump_header+0x5c/0x22e
 [<ffffffff810de08d>] ? trace_hardirqs_on+0xd/0x10
 [<ffffffff811b3381>] oom_kill_process+0x221/0x3f0
 [<ffffffff810901b7>] ? has_capability_noaudit+0x17/0x20
 [<ffffffff811b3acf>] out_of_memory+0x52f/0x560
 [<ffffffff811b377c>] ? out_of_memory+0x1dc/0x560
 [<ffffffff811ba004>] __alloc_pages_nodemask+0x1154/0x11b0
 [<ffffffff810813a1>] ? copy_process.part.30+0x121/0x1bf0
 [<ffffffff810813a1>] copy_process.part.30+0x121/0x1bf0
 [<ffffffff811ebb16>] ? handle_mm_fault+0xb36/0x13d0
 [<ffffffff810fb60d>] ? debug_lockdep_rcu_enabled+0x1d/0x20
 [<ffffffff81083066>] _do_fork+0xe6/0x6a0
 [<ffffffff810836c9>] SyS_clone+0x19/0x20
 [<ffffffff81003e13>] do_syscall_64+0x73/0x1e0
 [<ffffffff81858ec3>] entry_SYSCALL64_slow_path+0x25/0x25
Mem-Info:
active_anon:23909 inactive_anon:18 isolated_anon:0
 active_file:289985 inactive_file:101445 isolated_file:0
 unevictable:0 dirty:0 writeback:0 unstable:0
 slab_reclaimable:6696 slab_unreclaimable:22083
 mapped:381662 shmem:95 pagetables:21600 bounce:0
 free:8378 free_pcp:227 free_cma:0
Node 0 active_anon:95676kB inactive_anon:72kB active_file:1160056kB inactive_file:405792kB unevictable:0kB isolated(anon):0kB isolated(file):0kB mapped:1526812kB dirty:4kB writeback:0kB shmem:0kB shmem_thp
: 0kB shmem_pmdmapped: 0kB anon_thp: 380kB writeback_tmp:0kB unstable:0kB all_unreclaimable? no
Node 0 DMA free:2176kB min:204kB low:252kB high:300kB present:15992kB managed:15908kB mlocked:0kB slab_reclaimable:0kB slab_unreclaimable:2328kB kernel_stack:1472kB pagetables:2940kB bounce:0kB free_pcp:0k
B local_pcp:0kB free_cma:0kB node_pages_scanned:1668
lowmem_reserve[]: 0 493 493 1955
Node 0 DMA32 free:8188kB min:6492kB low:8112kB high:9732kB present:2080632kB managed:508600kB mlocked:0kB slab_reclaimable:26784kB slab_unreclaimable:86004kB kernel_stack:40704kB pagetables:83460kB bounce:
0kB free_pcp:208kB local_pcp:0kB free_cma:0kB node_pages_scanned:12000
lowmem_reserve[]: 0 0 0 1462
Node 0 Movable free:23648kB min:19256kB low:24068kB high:28880kB present:1535864kB managed:1500964kB mlocked:0kB slab_reclaimable:0kB slab_unreclaimable:0kB kernel_stack:0kB pagetables:0kB bounce:0kB free_
pcp:748kB local_pcp:0kB free_cma:0kB node_pages_scanned:12000
lowmem_reserve[]: 0 0 0 0
Node 0 DMA: 2*4kB (M) 0*8kB 2*16kB (UM) 2*32kB (UM) 0*64kB 2*128kB (UM) 1*256kB (U) 1*512kB (M) 1*1024kB (M) 0*2048kB 0*4096kB = 2152kB
Node 0 DMA32: 21*4kB (EH) 14*8kB (UMEH) 14*16kB (UMEH) 17*32kB (UM) 11*64kB (ME) 13*128kB (UME) 14*256kB (UME) 1*512kB (U) 1*1024kB (M) 0*2048kB 0*4096kB = 8452kB
Node 0 Movable: 87*4kB (M) 106*8kB (M) 82*16kB (M) 39*32kB (M) 11*64kB (M) 4*128kB (M) 0*256kB 1*512kB (M) 0*1024kB 1*2048kB (M) 4*4096kB (M) = 23916kB
Node 0 hugepages_total=0 hugepages_free=0 hugepages_surp=0 hugepages_size=2048kB
391491 total pagecache pages
0 pages in swap cache
Swap cache stats: add 0, delete 0, find 0/0
Free swap  = 0kB
Total swap = 0kB
908122 pages RAM
0 pages HighMem/MovableOnly
401754 pages reserved
0 pages cma reserved
0 pages hwpoisoned

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#1446515

FromMel Gorman <mgorman@techsingularity.net>
Date2016-07-19 16:30 +0200
Message-ID<rWEc2-57V-7@gated-at.bofh.it>
In reply to#1446234
On Tue, Jul 19, 2016 at 05:30:31PM +0900, Joonsoo Kim wrote:
> On Mon, Jul 18, 2016 at 03:27:14PM +0100, Mel Gorman wrote:
> > On Mon, Jul 18, 2016 at 01:11:22PM +0100, Mel Gorman wrote:
> > > The all_unreclaimable logic is related to the number of pages scanned
> > > but currently pages skipped contributes to pages scanned. That is one
> > > possibility. The other is that if all pages scanned are skipped then the
> > > OOM killer can believe there is zero progress.
> > > 
> > > Try this to start with;
> > > 
> > 
> > And if that fails, try this heavier handed version that will scan the full
> > LRU potentially to isolate at least a single page if it's available for
> > zone-constrained allocations. It's compile-tested only
> 
> I tested both patches but they don't work for me. Notable difference
> is that all_unreclaimable is now "no".
> 

Ok, that's good to know at least. It at least indicates that skips
accounted as scans are a contributory factor.

> Just attach the oops log from heavier version.
> 

Apparently, isolating at least one page is not enough. Please try the
following. If it fails, please post the test script you're using. I can
simulate what you describe (mapped reads combined with lots of forks)
but no guarantee I'll get it exactly right. I think it's ok to not
account skips as scans because the skips are already accounted for.

diff --git a/mm/vmscan.c b/mm/vmscan.c
index a6f31617a08c..0dc443b52228 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1415,7 +1415,7 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
 	LIST_HEAD(pages_skipped);
 
 	for (scan = 0; scan < nr_to_scan && nr_taken < nr_to_scan &&
-					!list_empty(src); scan++) {
+					!list_empty(src);) {
 		struct page *page;
 
 		page = lru_to_page(src);
@@ -1428,6 +1428,9 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
 			nr_skipped[page_zonenum(page)]++;
 			continue;
 		}
+`
+		/* Pages skipped do not contribute to scan */
+		scan++;
 
 		switch (__isolate_lru_page(page, mode)) {
 		case 0:
-- 
Mel Gorman
SUSE Labs

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