Re: [RFC] can we use vmalloc to alloc thread stack if compaction failed

[Xishi Qiu]

On 2016/7/28 15:20, Michal Hocko wrote:

> On Thu 28-07-16 15:08:26, Xishi Qiu wrote:
>> Usually THREAD_SIZE_ORDER is 2, it means we need to alloc 16kb continuous
>> physical memory during fork a new process.
>>
>> If the system's memory is very small, especially the smart phone, maybe there
>> is only 1G memory. So the free memory is very small and compaction is not
>> always success in slowpath(__alloc_pages_slowpath), then alloc thread stack
>> may be failed for memory fragment.
> 
> Well, with the current implementation of the page allocator those
> requests will not fail in most cases. The oom killer would be invoked in
> order to free up some memory.
> 

Hi Michal,

Yes, it success in most cases, but I did have seen this problem in some
stress-test.

DMA free:470628kB, but alloc 2 order block failed during fork a new process.
There are so many memory fragments and the large block may be soon taken by
others after compact because of stress-test.

--- dmesg messages ---
07-13 08:41:51.341 <4>[309805.658142s][pid:1361,cpu5,sManagerService]sManagerService: page allocation failure: order:2, mode:0x2000d1
07-13 08:41:51.346 <4>[309805.658142s][pid:1361,cpu5,sManagerService]CPU: 5 PID: 1361 Comm: sManagerService Tainted: G        W       4.1.18-g09f547b #1
07-13 08:41:51.347 <4>[309805.658142s][pid:1361,cpu5,sManagerService]TGID: 981 Comm: system_server
07-13 08:41:51.347 <4>[309805.658172s][pid:1361,cpu5,sManagerService]Hardware name: hi3650 (DT)
07-13 08:41:51.347 <0>[309805.658172s][pid:1361,cpu5,sManagerService]Call trace:
07-13 08:41:51.347 <4>[309805.658203s][pid:1361,cpu5,sManagerService][<ffffffc00008a0a4>] dump_backtrace+0x0/0x150
07-13 08:41:51.347 <4>[309805.658203s][pid:1361,cpu5,sManagerService][<ffffffc00008a214>] show_stack+0x20/0x28
07-13 08:41:51.347 <4>[309805.658203s][pid:1361,cpu5,sManagerService][<ffffffc000fc4034>] dump_stack+0x84/0xa8
07-13 08:41:51.347 <4>[309805.658203s][pid:1361,cpu5,sManagerService][<ffffffc00018af54>] warn_alloc_failed+0x10c/0x164
07-13 08:41:51.347 <4>[309805.658233s][pid:1361,cpu5,sManagerService][<ffffffc00018e778>] __alloc_pages_nodemask+0x5b4/0x888
07-13 08:41:51.347 <4>[309805.658233s][pid:1361,cpu5,sManagerService][<ffffffc00018eb84>] alloc_kmem_pages_node+0x44/0x50
07-13 08:41:51.347 <4>[309805.658233s][pid:1361,cpu5,sManagerService][<ffffffc00009fa78>] copy_process.part.46+0x140/0x15ac
07-13 08:41:51.347 <4>[309805.658233s][pid:1361,cpu5,sManagerService][<ffffffc0000a10a0>] do_fork+0xe8/0x444
07-13 08:41:51.347 <4>[309805.658264s][pid:1361,cpu5,sManagerService][<ffffffc0000a14e8>] SyS_clone+0x3c/0x48
07-13 08:41:51.347 <4>[309805.658264s][pid:1361,cpu5,sManagerService]Mem-Info:
07-13 08:41:51.347 <4>[309805.658264s][pid:1361,cpu5,sManagerService]active_anon:491074 inactive_anon:118072 isolated_anon:0
07-13 08:41:51.347 <4>[309805.658264s] active_file:19087 inactive_file:9843 isolated_file:0
07-13 08:41:51.347 <4>[309805.658264s] unevictable:322 dirty:20 writeback:0 unstable:0
07-13 08:41:51.347 <4>[309805.658264s] slab_reclaimable:11788 slab_unreclaimable:28068
07-13 08:41:51.347 <4>[309805.658264s] mapped:20633 shmem:4038 pagetables:10865 bounce:72
07-13 08:41:51.347 <4>[309805.658264s] free:118678 free_pcp:58 free_cma:0
07-13 08:41:51.347 <4>[309805.658294s][pid:1361,cpu5,sManagerService]DMA free:470628kB min:6800kB low:29116kB high:30816kB active_anon:1868540kB inactive_anon:376100kB active_file:292kB inactive_file:240kB unevictable:1080kB isolated(anon):0kB isolated(file):0kB present:3446780kB managed:3307056kB mlocked:1080kB dirty:80kB writeback:0kB mapped:7604kB shmem:14380kB slab_reclaimable:47152kB slab_unreclaimable:112268kB kernel_stack:28224kB pagetables:43460kB unstable:0kB bounce:288kB free_pcp:204kB local_pcp:0kB free_cma:0kB writeback_tmp:0kB pages_scanned:0 all_unreclaimable? no
07-13 08:41:51.347 <4>[309805.658294s][pid:1361,cpu5,sManagerService]lowmem_reserve[]: 0 415 415
07-13 08:41:51.347 <4>[309805.658294s][pid:1361,cpu5,sManagerService]Normal free:4084kB min:872kB low:3740kB high:3960kB active_anon:95756kB inactive_anon:96188kB active_file:76056kB inactive_file:39132kB unevictable:208kB isolated(anon):0kB isolated(file):0kB present:524288kB managed:425480kB mlocked:208kB dirty:0kB writeback:0kB mapped:74928kB shmem:1772kB slab_reclaimable:0kB slab_unreclaimable:4kB kernel_stack:0kB pagetables:0kB unstable:0kB bounce:0kB free_pcp:28kB local_pcp:0kB free_cma:0kB writeback_tmp:0kB pages_scanned:0 all_unreclaimable? no
07-13 08:41:51.347 <4>[309805.658294s][pid:1361,cpu5,sManagerService]lowmem_reserve[]: 0 0 0
07-13 08:41:51.347 <4>[309805.658325s][pid:1361,cpu5,sManagerService]DMA: 68324*4kB (UEM) 24706*8kB (UER) 2*16kB (U) 0*32kB 0*64kB 0*128kB 0*256kB 0*512kB 0*1024kB 0*2048kB 0*4096kB = 470976kB
07-13 08:41:51.347 <4>[309805.658355s][pid:1361,cpu5,sManagerService]Normal: 270*4kB (UMR) 82*8kB (UMR) 48*16kB (MR) 25*32kB (R) 12*64kB (R) 2*128kB (R) 1*256kB (R) 0*512kB 0*1024kB 0*2048kB 0*4096kB = 4584kB
07-13 08:41:51.347 <4>[309805.658386s][pid:1361,cpu5,sManagerService]38319 total pagecache pages
07-13 08:41:51.347 <4>[309805.658386s][pid:1361,cpu5,sManagerService]5384 pages in swap cache
07-13 08:41:51.347 <4>[309805.658386s][pid:1361,cpu5,sManagerService]Swap cache stats: add 628084, delete 622700, find 2187699/2264909
07-13 08:41:51.347 <4>[309805.658386s][pid:1361,cpu5,sManagerService]Free swap  = 0kB
07-13 08:41:51.348 <4>[309805.658416s][pid:1361,cpu5,sManagerService]Total swap = 524284kB
07-13 08:41:51.348 <4>[309805.658416s][pid:1361,cpu5,sManagerService]992767 pages RAM
07-13 08:41:51.348 <4>[309805.658416s][pid:1361,cpu5,sManagerService]0 pages HighMem/MovableOnly
07-13 08:41:51.348 <4>[309805.658416s][pid:1361,cpu5,sManagerService]51441 pages reserved
07-13 08:41:51.348 <4>[309805.658416s][pid:1361,cpu5,sManagerService]8192 pages cma reserved
07-13 08:41:51.767 <6>[309806.068298s][pid:2247,cpu6,notification-sq][I/sensorhub] shb_release ok

>> Can we use vmalloc to alloc thread stack if compaction failed in slowpath?
> 
> Not yet but Andy is working on this.
> 
>> e.g. Use vmalloc as a fallback if alloc_page/kamlloc failed.
>>
>> I think the performance may be a little regression, and any other problems?
>>
>> Thanks,
>> Xishi Qiu
>