Re: [PATCH] mm/page_owner: Remove drain_all_pages from init_early_allocated_pages

From: Michal Hocko <mhocko@suse.com>
To: Oscar Salvador <osalvador@techadventures.net>
Cc: linux-mm@kvack.org, vbabka@suse.cz, akpm@linux-foundation.org,
	ayush.m@samsung.com, Joonsoo Kim <js1304@gmail.com>
Subject: Re: [PATCH] mm/page_owner: Remove drain_all_pages from init_early_allocated_pages
Date: Tue, 9 Jan 2018 17:26:33 +0100	[thread overview]
Message-ID: <20180109162633.GM1732@dhcp22.suse.cz> (raw)
In-Reply-To: <20180109153921.GA13070@techadventures.net>

[CC Joonsoo]

On Tue 09-01-18 16:39:21, Oscar Salvador wrote:
> When setting page_owner = on, the following warning can be seen in the boot log:
> 
>  WARNING: CPU: 0 PID: 0 at mm/page_alloc.c:2537 drain_all_pages+0x171/0x1a0
>  Modules linked in:
>  CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.15.0-rc7-next-20180109-1-default+ #7
>  Hardware name: Dell Inc. Latitude E7470/0T6HHJ, BIOS 1.11.3 11/09/2016
>  RIP: 0010:drain_all_pages+0x171/0x1a0
>  RSP: 0000:ffffffff82003ea8 EFLAGS: 00010246
>  RAX: 000000000000000f RBX: ffffffffffffffff RCX: ffffffff8205b388
>  RDX: 0000000000000001 RSI: 0000000000000096 RDI: 0000000000000202
>  RBP: 0000000000000000 R08: 0000000000000000 R09: 00000000000000af
>  R10: 0000000000000004 R11: 00000000000000ae R12: ffff88024dfdcec0
>  R13: ffffffff82530740 R14: 0000000000000000 R15: 00000000a8831448
>  FS:  0000000000000000(0000) GS:ffff88024dc00000(0000) knlGS:0000000000000000
>  CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>  CR2: ffff88024dfff000 CR3: 000000000200a001 CR4: 00000000000606b0
>  DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>  DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
>  Call Trace:
>   init_page_owner+0x4e/0x260
>   start_kernel+0x3e6/0x4a6
>   ? set_init_arg+0x55/0x55
>   secondary_startup_64+0xa5/0xb0
>  Code: c5 ed ff 89 df 48 c7 c6 20 3b 71 82 e8 f9 4b 52 00 3b 05 d7 0b f8 00 89 c3 72 d5 5b 5d 41 5
>  ---[ end trace 45da7f0cb4aef07b ]---
> 
> This warning is showed because we are calling drain_all_pages() in
> init_early_allocated_pages(), but mm_percpu_wq is not up yet,
> it is being set up later on in kernel_init_freeable() -> init_mm_internals().

I _think_ the patch is correct. The changelog should explain, _why_
removing drain_all_pages is OK. Joonsoo what was the reason to put it
here in the first place? I do not see any real reason. This is an init
code and we shouldn't have any pages on those caches anyway. Moreover I
fail to see why the fact they are on the pcp caches mattered at all.

> Signed-off-by: Oscar Salvador <osalvador@techadventures.net>
> ---
>  mm/page_owner.c | 1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/mm/page_owner.c b/mm/page_owner.c
> index 8602fb41b293..69f83fc763bb 100644
> --- a/mm/page_owner.c
> +++ b/mm/page_owner.c
> @@ -616,7 +616,6 @@ static void init_early_allocated_pages(void)
>  {
>  	pg_data_t *pgdat;
>  
> -	drain_all_pages(NULL);
>  	for_each_online_pgdat(pgdat)
>  		init_zones_in_node(pgdat);
>  }
> -- 
> 2.13.5
> 

-- 
Michal Hocko
SUSE Labs

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