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Subject: Re: [PATCH v3] page_alloc: consider highatomic reserve in wmartermark
 fast
To:     Jaewon Kim <jaewon31.kim@samsung.com>, bhe@redhat.com,
        mgorman@techsingularity.net, minchan@kernel.org, mgorman@suse.de,
        hannes@cmpxchg.org, akpm@linux-foundation.org
Cc:     linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        jaewon31.kim@gmail.com, ytk.lee@samsung.com,
        cmlaika.kim@samsung.com
References: <CGME20200616080413epcas1p4c8ff98e9a79c59fd9a43db6a9d507417@epcas1p4.samsung.com>
 <20200617020550.23159-1-jaewon31.kim@samsung.com>
From:   Vlastimil Babka <vbabka@suse.cz>
Message-ID: <8f809f31-47bb-9f48-1b7d-e0a3ae14e6b9@suse.cz>
Date:   Tue, 16 Jun 2020 12:21:54 +0200
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On 6/17/20 4:05 AM, Jaewon Kim wrote:

Please fix typo "wmartermark" in subject.

> 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. Additionally introduce
> __zone_watermark_unusable_free to factor out common parts between
> zone_watermark_fast and __zone_watermark_ok.
> 
> This is an example of ALLOC_HARDER allocation failure using v4.19 based
> kernel.
> 
> <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

These are better to read after removing the timestamp and process info part,
i.e. "<4>[ 6207.637668]  [3:  Binder:9343_3:22875]" (also in the other examples
below).

> This is an example of ALLOC_NO_WATERMARKS allocation failure using v4.14
> based kernel.
> 
> [ 4738.329298] kswapd0: page allocation failure: order:0, mode:0x140000a(GFP_NOIO|__GFP_HIGHMEM|__GFP_MOVABLE), nodemask=(null)
> [ 4738.329325] kswapd0 cpuset=/ mems_allowed=0
> [ 4738.329339] CPU: 4 PID: 1221 Comm: kswapd0 Not tainted 4.14.113-18770262-userdebug #1
> [ 4738.329350] Call trace:
> [ 4738.329366] [<0000000000000000>] dump_backtrace+0x0/0x248
> [ 4738.329377] [<0000000000000000>] show_stack+0x18/0x20
> [ 4738.329390] [<0000000000000000>] __dump_stack+0x20/0x28
> [ 4738.329398] [<0000000000000000>] dump_stack+0x68/0x90
> [ 4738.329409] [<0000000000000000>] warn_alloc+0x104/0x198
> [ 4738.329417] [<0000000000000000>] __alloc_pages_nodemask+0xdc0/0xdf0
> [ 4738.329427] [<0000000000000000>] zs_malloc+0x148/0x3d0
> [ 4738.329438] [<0000000000000000>] zram_bvec_rw+0x410/0x798
> [ 4738.329446] [<0000000000000000>] zram_rw_page+0x88/0xdc
> [ 4738.329455] [<0000000000000000>] bdev_write_page+0x70/0xbc
> [ 4738.329463] [<0000000000000000>] __swap_writepage+0x58/0x37c
> [ 4738.329469] [<0000000000000000>] swap_writepage+0x40/0x4c
> [ 4738.329478] [<0000000000000000>] shrink_page_list+0xc30/0xf48
> [ 4738.329486] [<0000000000000000>] shrink_inactive_list+0x2b0/0x61c
> [ 4738.329494] [<0000000000000000>] shrink_node_memcg+0x23c/0x618
> [ 4738.329501] [<0000000000000000>] shrink_node+0x1c8/0x304
> [ 4738.329509] [<0000000000000000>] kswapd+0x680/0x7c4
> [ 4738.329518] [<0000000000000000>] kthread+0x110/0x120
> [ 4738.329527] [<0000000000000000>] ret_from_fork+0x10/0x18
> [ 4738.329538] Mem-Info:
> [ 4738.329574] active_anon:111826 inactive_anon:65557 isolated_anon:0\x0a active_file:44260 inactive_file:83422 isolated_file:0\x0a unevictable:4158 dirty:117 writeback:0 unstable:0\x0a            slab_reclaimable:13943 slab_unreclaimable:43315\x0a mapped:102511 shmem:3299 pagetables:19566 bounce:0\x0a free:3510 free_pcp:553 free_cma:0
> [ 4738.329593] Node 0 active_anon:447304kB inactive_anon:262228kB active_file:177040kB inactive_file:333688kB unevictable:16632kB isolated(anon):0kB isolated(file):0kB mapped:410044kB d irty:468kB writeback:0kB shmem:13196kB writeback_tmp:0kB unstable:0kB all_unreclaimable? no
> [ 4738.329603] Normal free:14040kB min:7440kB low:94500kB high:98136kB reserved_highatomic:32768KB active_anon:447336kB inactive_anon:261668kB active_file:177572kB inactive_file:333768k           B unevictable:16632kB writepending:480kB present:4081664kB managed:3637088kB mlocked:16632kB kernel_stack:47072kB pagetables:78264kB bounce:0kB free_pcp:2280kB local_pcp:720kB free_cma:0kB        [ 4738.329607] lowmem_reserve[]: 0 0
> [ 4738.329615] Normal: 860*4kB (H) 453*8kB (H) 180*16kB (H) 26*32kB (H) 34*64kB (H) 6*128kB (H) 2*256kB (H) 0*512kB 0*1024kB 0*2048kB 0*4096kB = 14232kB
> 
> 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
> 
> Reported-by: Yong-Taek Lee <ytk.lee@samsung.com>
> Suggested-by: Minchan Kim <minchan@kernel.org>
> Signed-off-by: Jaewon Kim <jaewon31.kim@samsung.com>

Acked-by: Vlastimil Babka <vbabka@suse.cz>

> ---
> v3: change log in description to one having reserved_highatomic
>     change comment in code
> v2: factor out common part
> v1: consider highatomic reserve
> ---
>  mm/page_alloc.c | 66 +++++++++++++++++++++++++++----------------------
>  1 file changed, 36 insertions(+), 30 deletions(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 48eb0f1410d4..fe83f88ce188 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -3487,6 +3487,29 @@ static noinline bool should_fail_alloc_page(gfp_t gfp_mask, unsigned int order)
>  }
>  ALLOW_ERROR_INJECTION(should_fail_alloc_page, TRUE);
>  
> +static inline long __zone_watermark_unusable_free(struct zone *z,
> +				unsigned int order, unsigned int alloc_flags)
> +{
> +	const bool alloc_harder = (alloc_flags & (ALLOC_HARDER|ALLOC_OOM));
> +	long unusable_free = (1 << order) - 1;
> +
> +	/*
> +	 * If the caller does not have rights to ALLOC_HARDER then subtract
> +	 * the high-atomic reserves. This will over-estimate the size of the
> +	 * atomic reserve but it avoids a search.
> +	 */
> +	if (likely(!alloc_harder))
> +		unusable_free += z->nr_reserved_highatomic;
> +
> +#ifdef CONFIG_CMA
> +	/* If allocation can't use CMA areas don't use free CMA pages */
> +	if (!(alloc_flags & ALLOC_CMA))
> +		unusable_free += zone_page_state(z, NR_FREE_CMA_PAGES);
> +#endif
> +
> +	return unusable_free;
> +}
> +
>  /*
>   * Return true if free base pages are above 'mark'. For high-order checks it
>   * will return true of the order-0 watermark is reached and there is at least
> @@ -3502,19 +3525,12 @@ bool __zone_watermark_ok(struct zone *z, unsigned int order, unsigned long mark,
>  	const bool alloc_harder = (alloc_flags & (ALLOC_HARDER|ALLOC_OOM));
>  
>  	/* free_pages may go negative - that's OK */
> -	free_pages -= (1 << order) - 1;
> +	free_pages -= __zone_watermark_unusable_free(z, order, alloc_flags);
>  
>  	if (alloc_flags & ALLOC_HIGH)
>  		min -= min / 2;
>  
> -	/*
> -	 * If the caller does not have rights to ALLOC_HARDER then subtract
> -	 * the high-atomic reserves. This will over-estimate the size of the
> -	 * atomic reserve but it avoids a search.
> -	 */
> -	if (likely(!alloc_harder)) {
> -		free_pages -= z->nr_reserved_highatomic;
> -	} else {
> +	if (unlikely(alloc_harder)) {
>  		/*
>  		 * OOM victims can try even harder than normal ALLOC_HARDER
>  		 * users on the grounds that it's definitely going to be in
> @@ -3527,13 +3543,6 @@ bool __zone_watermark_ok(struct zone *z, unsigned int order, unsigned long mark,
>  			min -= min / 4;
>  	}
>  
> -
> -#ifdef CONFIG_CMA
> -	/* If allocation can't use CMA areas don't use free CMA pages */
> -	if (!(alloc_flags & ALLOC_CMA))
> -		free_pages -= zone_page_state(z, NR_FREE_CMA_PAGES);
> -#endif
> -
>  	/*
>  	 * Check watermarks for an order-0 allocation request. If these
>  	 * are not met, then a high-order request also cannot go ahead
> @@ -3582,25 +3591,22 @@ static inline bool zone_watermark_fast(struct zone *z, unsigned int order,
>  				unsigned long mark, int highest_zoneidx,
>  				unsigned int alloc_flags)
>  {
> -	long free_pages = zone_page_state(z, NR_FREE_PAGES);
> -	long cma_pages = 0;
> +	long free_pages;
> +	long unusable_free;
>  
> -#ifdef CONFIG_CMA
> -	/* If allocation can't use CMA areas don't use free CMA pages */
> -	if (!(alloc_flags & ALLOC_CMA))
> -		cma_pages = zone_page_state(z, NR_FREE_CMA_PAGES);
> -#endif
> +	free_pages = zone_page_state(z, NR_FREE_PAGES);
> +	unusable_free = __zone_watermark_unusable_free(z, order, alloc_flags);
>  
>  	/*
>  	 * Fast check for order-0 only. If this fails then the reserves
> -	 * need to be calculated. There is a corner case where the check
> -	 * passes but only the high-order atomic reserve are free. If
> -	 * the caller is !atomic then it'll uselessly search the free
> -	 * list. That corner case is then slower but it is harmless.
> +	 * need to be calculated.
>  	 */
> -	if (!order && (free_pages - cma_pages) >
> -				mark + z->lowmem_reserve[highest_zoneidx])
> -		return true;
> +	if (!order) {
> +		long fast_free = free_pages - unusable_free;
> +
> +		if (fast_free > mark + z->lowmem_reserve[highest_zoneidx])
> +			return true;
> +	}
>  
>  	return __zone_watermark_ok(z, order, mark, highest_zoneidx, alloc_flags,
>  					free_pages);
>