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Date:   Fri, 12 Jun 2020 16:55:07 +0900
From:   Jaewon Kim <jaewon31.kim@...sung.com>
To:     Minchan Kim <minchan@...nel.org>
Cc:     mgorman@...hsingularity.net, mgorman@...e.de, hannes@...xchg.org,
        akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, jaewon31.kim@...il.com,
        ytk.lee@...sung.com, cmlaika.kim@...sung.com
Subject: Re: [PATCH] page_alloc: consider highatomic reserve in wmartermark
 fast



On 2020년 06월 12일 16:40, Minchan Kim wrote:
> On Fri, Jun 12, 2020 at 04:03:41PM +0900, Jaewon Kim wrote:
>>
>> On 2020년 06월 12일 15:55, Minchan Kim wrote:
>>> On Thu, Jun 11, 2020 at 05:54:12PM +0900, Jaewon Kim wrote:
>>>> On 2020년 06월 10일 10:21, Minchan Kim wrote:
>>>>> Hi Jaewon,
>>>>>
>>>>> On Tue, Jun 09, 2020 at 06:51:28PM +0900, Jaewon Kim wrote:
>>>>>> zone_watermark_fast was introduced by commit 48ee5f3696f6 ("mm,
>>>>>> page_alloc: shortcut watermark checks for order-0 pages"). The commit
>>>>>> simply checks if free pages is bigger than watermark without additional
>>>>>> calculation such like reducing watermark.
>>>>>>
>>>>>> It considered free cma pages but it did not consider highatomic
>>>>>> reserved. This may incur exhaustion of free pages except high order
>>>>>> atomic free pages.
>>>>>>
>>>>>> Assume that reserved_highatomic pageblock is bigger than watermark min,
>>>>>> and there are only few free pages except high order atomic free. Because
>>>>>> zone_watermark_fast passes the allocation without considering high order
>>>>>> atomic free, normal reclaimable allocation like GFP_HIGHUSER will
>>>>>> consume all the free pages. Then finally order-0 atomic allocation may
>>>>>> fail on allocation.
>>>>>>
>>>>>> This means watermark min is not protected against non-atomic allocation.
>>>>>> The order-0 atomic allocation with ALLOC_HARDER unwantedly can be
>>>>>> failed. Additionally the __GFP_MEMALLOC allocation with
>>>>>> ALLOC_NO_WATERMARKS also can be failed.
>>>>>>
>>>>>> To avoid the problem, zone_watermark_fast should consider highatomic
>>>>>> reserve. If the actual size of high atomic free is counted accurately
>>>>>> like cma free, we may use it. On this patch just use
>>>>>> nr_reserved_highatomic.
>>>>>>
>>>>>> This is trace log which shows GFP_HIGHUSER consumes free pages right
>>>>>> before ALLOC_NO_WATERMARKS.
>>>>>>
>>>>>>   <...>-22275 [006] ....   889.213383: mm_page_alloc: page=00000000d2be5665 pfn=970744 order=0 migratetype=0 nr_free=3650 gfp_flags=GFP_HIGHUSER|__GFP_ZERO
>>>>>>   <...>-22275 [006] ....   889.213385: mm_page_alloc: page=000000004b2335c2 pfn=970745 order=0 migratetype=0 nr_free=3650 gfp_flags=GFP_HIGHUSER|__GFP_ZERO
>>>>>>   <...>-22275 [006] ....   889.213387: mm_page_alloc: page=00000000017272e1 pfn=970278 order=0 migratetype=0 nr_free=3650 gfp_flags=GFP_HIGHUSER|__GFP_ZERO
>>>>>>   <...>-22275 [006] ....   889.213389: mm_page_alloc: page=00000000c4be79fb pfn=970279 order=0 migratetype=0 nr_free=3650 gfp_flags=GFP_HIGHUSER|__GFP_ZERO
>>>>>>   <...>-22275 [006] ....   889.213391: mm_page_alloc: page=00000000f8a51d4f pfn=970260 order=0 migratetype=0 nr_free=3650 gfp_flags=GFP_HIGHUSER|__GFP_ZERO
>>>>>>   <...>-22275 [006] ....   889.213393: mm_page_alloc: page=000000006ba8f5ac pfn=970261 order=0 migratetype=0 nr_free=3650 gfp_flags=GFP_HIGHUSER|__GFP_ZERO
>>>>>>   <...>-22275 [006] ....   889.213395: mm_page_alloc: page=00000000819f1cd3 pfn=970196 order=0 migratetype=0 nr_free=3650 gfp_flags=GFP_HIGHUSER|__GFP_ZERO
>>>>>>   <...>-22275 [006] ....   889.213396: mm_page_alloc: page=00000000f6b72a64 pfn=970197 order=0 migratetype=0 nr_free=3650 gfp_flags=GFP_HIGHUSER|__GFP_ZERO
>>>>>> kswapd0-1207  [005] ...1   889.213398: mm_page_alloc: page= (null) pfn=0 order=0 migratetype=1 nr_free=3650 gfp_flags=GFP_NOWAIT|__GFP_HIGHMEM|__GFP_NOWARN|__GFP_MOVABLE
>>>>>>
>>>>>> This is an example of ALLOC_HARDER allocation failure.
>>>>>>
>>>>>> <4>[ 6207.637280]  [3:  Binder:9343_3:22875] Binder:9343_3: page allocation failure: order:0, mode:0x480020(GFP_ATOMIC), nodemask=(null)
>>>>>> <4>[ 6207.637311]  [3:  Binder:9343_3:22875] Call trace:
>>>>>> <4>[ 6207.637346]  [3:  Binder:9343_3:22875] [<ffffff8008f40f8c>] dump_stack+0xb8/0xf0
>>>>>> <4>[ 6207.637356]  [3:  Binder:9343_3:22875] [<ffffff8008223320>] warn_alloc+0xd8/0x12c
>>>>>> <4>[ 6207.637365]  [3:  Binder:9343_3:22875] [<ffffff80082245e4>] __alloc_pages_nodemask+0x120c/0x1250
>>>>>> <4>[ 6207.637374]  [3:  Binder:9343_3:22875] [<ffffff800827f6e8>] new_slab+0x128/0x604
>>>>>> <4>[ 6207.637381]  [3:  Binder:9343_3:22875] [<ffffff800827b0cc>] ___slab_alloc+0x508/0x670
>>>>>> <4>[ 6207.637387]  [3:  Binder:9343_3:22875] [<ffffff800827ba00>] __kmalloc+0x2f8/0x310
>>>>>> <4>[ 6207.637396]  [3:  Binder:9343_3:22875] [<ffffff80084ac3e0>] context_struct_to_string+0x104/0x1cc
>>>>>> <4>[ 6207.637404]  [3:  Binder:9343_3:22875] [<ffffff80084ad8fc>] security_sid_to_context_core+0x74/0x144
>>>>>> <4>[ 6207.637412]  [3:  Binder:9343_3:22875] [<ffffff80084ad880>] security_sid_to_context+0x10/0x18
>>>>>> <4>[ 6207.637421]  [3:  Binder:9343_3:22875] [<ffffff800849bd80>] selinux_secid_to_secctx+0x20/0x28
>>>>>> <4>[ 6207.637430]  [3:  Binder:9343_3:22875] [<ffffff800849109c>] security_secid_to_secctx+0x3c/0x70
>>>>>> <4>[ 6207.637442]  [3:  Binder:9343_3:22875] [<ffffff8008bfe118>] binder_transaction+0xe68/0x454c
>>>>>> <4>[ 6207.637569]  [3:  Binder:9343_3:22875] Mem-Info:
>>>>>> <4>[ 6207.637595]  [3:  Binder:9343_3:22875] active_anon:102061 inactive_anon:81551 isolated_anon:0
>>>>>> <4>[ 6207.637595]  [3:  Binder:9343_3:22875]  active_file:59102 inactive_file:68924 isolated_file:64
>>>>>> <4>[ 6207.637595]  [3:  Binder:9343_3:22875]  unevictable:611 dirty:63 writeback:0 unstable:0
>>>>>> <4>[ 6207.637595]  [3:  Binder:9343_3:22875]  slab_reclaimable:13324 slab_unreclaimable:44354
>>>>>> <4>[ 6207.637595]  [3:  Binder:9343_3:22875]  mapped:83015 shmem:4858 pagetables:26316 bounce:0
>>>>>> <4>[ 6207.637595]  [3:  Binder:9343_3:22875]  free:2727 free_pcp:1035 free_cma:178
>>>>>> <4>[ 6207.637616]  [3:  Binder:9343_3:22875] Node 0 active_anon:408244kB inactive_anon:326204kB active_file:236408kB inactive_file:275696kB unevictable:2444kB isolated(anon):0kB isolated(file):256kB mapped:332060kB dirty:252kB writeback:0kB shmem:19432kB writeback_tmp:0kB unstable:0kB all_unreclaimable? no
>>>>>> <4>[ 6207.637627]  [3:  Binder:9343_3:22875] Normal free:10908kB min:6192kB low:44388kB high:47060kB active_anon:409160kB inactive_anon:325924kB active_file:235820kB inactive_file:276628kB unevictable:2444kB writepending:252kB present:3076096kB managed:2673676kB mlocked:2444kB kernel_stack:62512kB pagetables:105264kB bounce:0kB free_pcp:4140kB local_pcp:40kB free_cma:712kB
>>>>>> <4>[ 6207.637632]  [3:  Binder:9343_3:22875] lowmem_reserve[]: 0 0
>>>>>> <4>[ 6207.637637]  [3:  Binder:9343_3:22875] Normal: 505*4kB (H) 357*8kB (H) 201*16kB (H) 65*32kB (H) 1*64kB (H) 0*128kB 0*256kB 0*512kB 0*1024kB 0*2048kB 0*4096kB = 10236kB
>>>>>> <4>[ 6207.637655]  [3:  Binder:9343_3:22875] 138826 total pagecache pages
>>>>>> <4>[ 6207.637663]  [3:  Binder:9343_3:22875] 5460 pages in swap cache
>>>>>> <4>[ 6207.637668]  [3:  Binder:9343_3:22875] Swap cache stats: add 8273090, delete 8267506, find 1004381/4060142
>>>>>>
>>>>>> This is an example of ALLOC_NO_WATERMARKS allocation failure.
>>>>>>
>>>>>> <6>[  156.701551]  [4:        kswapd0: 1209] kswapd0 cpuset=/ mems_allowed=0
>>>>>> <4>[  156.701563]  [4:        kswapd0: 1209] CPU: 4 PID: 1209 Comm: kswapd0 Tainted: G        W       4.14.113-18113966 #1
>>>>>> <4>[  156.701572]  [4:        kswapd0: 1209] Call trace:
>>>>>> <4>[  156.701605]  [4:        kswapd0: 1209] [<0000000000000000>] dump_stack+0x68/0x90
>>>>>> <4>[  156.701612]  [4:        kswapd0: 1209] [<0000000000000000>] warn_alloc+0x104/0x198
>>>>>> <4>[  156.701617]  [4:        kswapd0: 1209] [<0000000000000000>] __alloc_pages_nodemask+0xdc0/0xdf0
>>>>>> <4>[  156.701623]  [4:        kswapd0: 1209] [<0000000000000000>] zs_malloc+0x148/0x3d0
>>>>>> <4>[  156.701630]  [4:        kswapd0: 1209] [<0000000000000000>] zram_bvec_rw+0x250/0x568
>>>>>> <4>[  156.701634]  [4:        kswapd0: 1209] [<0000000000000000>] zram_rw_page+0x8c/0xe0
>>>>>> <4>[  156.701640]  [4:        kswapd0: 1209] [<0000000000000000>] bdev_write_page+0x70/0xbc
>>>>>> <4>[  156.701645]  [4:        kswapd0: 1209] [<0000000000000000>] __swap_writepage+0x58/0x37c
>>>>>> <4>[  156.701649]  [4:        kswapd0: 1209] [<0000000000000000>] swap_writepage+0x40/0x4c
>>>>>> <4>[  156.701654]  [4:        kswapd0: 1209] [<0000000000000000>] shrink_page_list+0xc3c/0xf54
>>>>>> <4>[  156.701659]  [4:        kswapd0: 1209] [<0000000000000000>] shrink_inactive_list+0x2b0/0x61c
>>>>>> <4>[  156.701664]  [4:        kswapd0: 1209] [<0000000000000000>] shrink_node_memcg+0x23c/0x618
>>>>>> <4>[  156.701668]  [4:        kswapd0: 1209] [<0000000000000000>] shrink_node+0x1c8/0x304
>>>>>> <4>[  156.701673]  [4:        kswapd0: 1209] [<0000000000000000>] kswapd+0x680/0x7c4
>>>>>> <4>[  156.701679]  [4:        kswapd0: 1209] [<0000000000000000>] kthread+0x110/0x120
>>>>>> <4>[  156.701684]  [4:        kswapd0: 1209] [<0000000000000000>] ret_from_fork+0x10/0x18
>>>>>> <4>[  156.701689]  [4:        kswapd0: 1209] Mem-Info:
>>>>>> <4>[  156.701712]  [4:        kswapd0: 1209] active_anon:88690 inactive_anon:88630 isolated_anon:0
>>>>>> <4>[  156.701712]  [4:        kswapd0: 1209]  active_file:99173 inactive_file:169305 isolated_file:32
>>>>>> <4>[  156.701712]  [4:        kswapd0: 1209]  unevictable:48292 dirty:538 writeback:38 unstable:0
>>>>>> <4>[  156.701712]  [4:        kswapd0: 1209]  slab_reclaimable:15131 slab_unreclaimable:47762
>>>>>> <4>[  156.701712]  [4:        kswapd0: 1209]  mapped:274654 shmem:2824 pagetables:25088 bounce:0
>>>>>> <4>[  156.701712]  [4:        kswapd0: 1209]  free:2489 free_pcp:444 free_cma:3
>>>>>> <4>[  156.701728]  [4:        kswapd0: 1209] Node 0 active_anon:354760kB inactive_anon:354520kB active_file:396692kB inactive_file:677220kB unevictable:193168kB isolated(anon):0kB isolated(file):128kB mapped:1098616kB dirty:2152kB writeback:152kB shmem:11296kB writeback_tmp:0kB unstable:0kB all_unreclaimable? no
>>>>>> <4>[  156.701738]  [4:        kswapd0: 1209] Normal free:9956kB min:7428kB low:93440kB high:97032kB active_anon:355176kB inactive_anon:354580kB active_file:396196kB inactive_file:677284kB unevictable:193168kB writepending:2304kB present:4081664kB managed:3593324kB mlocked:193168kB kernel_stack:55008kB pagetables:100352kB bounce:0kB free_pcp:1776kB local_pcp:656kB free_cma:12kB
>>>>>> <4>[  156.701741]  [4:        kswapd0: 1209] lowmem_reserve[]: 0 0
>>>>>> <4>[  156.701747]  [4:        kswapd0: 1209] Normal: 196*4kB (H) 141*8kB (H) 109*16kB (H) 63*32kB (H) 20*64kB (H) 8*128kB (H) 2*256kB (H) 1*512kB (H) 0*1024kB 0*2048kB 0*4096kB = 9000kB
>>>>>>
>>>>>> Signed-off-by: Jaewon Kim <jaewon31.kim@...sung.com>
>>>>>> Reported-by: Yong-Taek Lee <ytk.lee@...sung.com>
>>>>>> ---
>>>>>>  mm/page_alloc.c | 13 +++++++++++--
>>>>>>  1 file changed, 11 insertions(+), 2 deletions(-)
>>>>>>
>>>>>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>>>>>> index 13cc653122b7..00869378d387 100644
>>>>>> --- a/mm/page_alloc.c
>>>>>> +++ b/mm/page_alloc.c
>>>>>> @@ -3553,6 +3553,11 @@ static inline bool zone_watermark_fast(struct zone *z, unsigned int order,
>>>>>>  {
>>>>>>  	long free_pages = zone_page_state(z, NR_FREE_PAGES);
>>>>>>  	long cma_pages = 0;
>>>>>> +	long highatomic = 0;
>>>>>> +	const bool alloc_harder = (alloc_flags & (ALLOC_HARDER|ALLOC_OOM));
>>>>>> +
>>>>>> +	if (likely(!alloc_harder))
>>>>>> +		highatomic = z->nr_reserved_highatomic;
>>>>>>  
>>>>>>  #ifdef CONFIG_CMA
>>>>>>  	/* If allocation can't use CMA areas don't use free CMA pages */
>>>>>> @@ -3567,8 +3572,12 @@ static inline bool zone_watermark_fast(struct zone *z, unsigned int order,
>>>>>>  	 * the caller is !atomic then it'll uselessly search the free
>>>>>>  	 * list. That corner case is then slower but it is harmless.
>>>>>>  	 */
>>>>>> -	if (!order && (free_pages - cma_pages) > mark + z->lowmem_reserve[classzone_idx])
>>>>>> -		return true;
>>>>>> +	if (!order) {
>>>>>> +		long fast_free = free_pages - cma_pages - highatomic;
>>>>> With your change, it seems we share most code for getting free_pages 
>>>>> between zone_watermark_fast and __zone_watermark_ok. Only difference
>>>>> between them is min calculation. If so, can we share most code between
>>>>> them via introducing like __zone_watermark_free static inline function?
>>>>> So, we didn't miss one place in future if we change something.
>>>>>
>>>> Hello thank you for your comment.
>>>>
>>>> I tried to share some code.
>>>> Because __zone_watermark_ok gets free pages as argument,
>>>> I just could make a function calculating unusable free.
>>>>
>>>> static inline long __zone_watermark_unusable_free(struct zone *z,
>>>>                                                     unsigned int alloc_flags)
>>>>
>>>> on zone_watermark_fast
>>>> free_pages -= __zone_watermark_unusable_free(z, alloc_flags);
>>>>
>>>> on __zone_watermark_ok
>>>> free_pages -= __zone_watermark_unusable_free(z, alloc_flags);
>>> Don't you need order argument?
>> Yes I actually I also took a consideration for it.
>>
>> If I keep existing logic of zone_watermark_fast,
>> following code in __zone_watermark_ok is not needed for __zone_watermark_unusable_free
>>   free_pages -= (1 << order) - 1;
>>
>> But if __zone_watermark_unusable_free should return
>> all unusable free, the order size should be included.
>>
>> Seems not critical but I want to hear opensource opinion.
> I don't think it could make measurable regression and if we want to
> factor it out, it would be better to be self-contained. To me, it
> looks weird if we need one more logic to consider *order* after
> __zone_watermark_unusable_free. IMHO, if we couldn't make it neat,
> the open-code like as-is would be better.8idfdff
> Since I am not strong against of either way, up to you.
Than you for your opinion. I actually agree on you with that.
Let me include the order and share v2 patch.

Thank you
Jaewon Kim
>
> Thanks.
>
>

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