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Date:   Fri, 12 Jun 2020 00:40:40 -0700
From:   Minchan Kim <minchan@kernel.org>
To:     Jaewon Kim <jaewon31.kim@samsung.com>
Cc:     mgorman@techsingularity.net, mgorman@suse.de, hannes@cmpxchg.org,
        akpm@linux-foundation.org, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, jaewon31.kim@gmail.com,
        ytk.lee@samsung.com, cmlaika.kim@samsung.com
Subject: Re: [PATCH] page_alloc: consider highatomic reserve in wmartermark
 fast
Message-ID: <20200612074040.GA98223@google.com>
References: <CGME20200609095139epcas1p17f9c213de6daf25fe848921bc70481c0@epcas1p1.samsung.com>
 <20200609095128.8112-1-jaewon31.kim@samsung.com>
 <20200610012112.GA239587@google.com>
 <5EE1F134.4090001@samsung.com>
 <20200612065523.GA92598@google.com>
 <5EE328CD.2060100@samsung.com>
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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@samsung.com>
> >>>> Reported-by: Yong-Taek Lee <ytk.lee@samsung.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.
Since I am not strong against of either way, up to you.

Thanks.