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Date: Tue, 20 Feb 2024 11:33:04 +0900
From: Byungchul Park <byungchul@sk.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: "Huang, Ying" <ying.huang@intel.com>, mingo@redhat.com,
	peterz@infradead.org, juri.lelli@redhat.com,
	vincent.guittot@linaro.org, dietmar.eggemann@arm.com,
	rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de,
	bristot@redhat.com, vschneid@redhat.com,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	kernel_team@skhynix.com
Subject: Re: [PATCH v4] sched/numa, mm: do not try to migrate memory to
 memoryless nodes
Message-ID: <20240220023304.GF65758@system.software.com>
References: <20240219041920.1183-1-byungchul@sk.com>
 <87o7ccrghz.fsf@yhuang6-desk2.ccr.corp.intel.com>
 <20240219174508.bc6256248a163c3ab9a58369@linux-foundation.org>
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On Mon, Feb 19, 2024 at 05:45:08PM -0800, Andrew Morton wrote:
> On Mon, 19 Feb 2024 16:43:36 +0800 "Huang, Ying" <ying.huang@intel.com> wrote:
> 
> > > +	/*
> > > +	 * Cannot migrate to memoryless nodes.
> > > +	 */
> > > +	if (!node_state(dst_nid, N_MEMORY))
> > > +		return false;
> > > +
> > >  	/*
> > >  	 * The pages in slow memory node should be migrated according
> > >  	 * to hot/cold instead of private/shared.
> > 
> > Good catch!
> > 
> > IIUC, you will use patch as fix to the issue in
> > 
> > https://lore.kernel.org/lkml/20240216111502.79759-1-byungchul@sk.com/
> > 
> > If so, we need the Fixes: tag to make it land in -stable properly.
> 
> Yes, this changelog is missing rather a lot of important information.
> 
> I pulled together the below, please check.

To make it more clear, I need to explain it more. I posted the following
two patches while resolving the oops issue. However, two are going on
for different purposes.

1) https://lkml.kernel.org/r/20240219041920.1183-1-byungchul@sk.com

   I started this patch as the fix for the oops. However, I found the
   root cause comes from using -1 as an array index. So let the root 
   cause fix go with another thread, 2). Nevertheless, 1) is still
   necessary as a *reasonable optimization* but not the real fix any
   more.

2) https://lkml.kernel.org/r/20240216111502.79759-1-byungchul@sk.com

   I found the root cause of the oops comes from using -1 as an array
   index. So moved all the oops message, Fixes: tag, and cc stable to
   here. Long story short, 2) is the *real fix* for the oops.

	Byungchul

> From: Byungchul Park <byungchul@sk.com>
> Subject: sched/numa, mm: do not try to migrate memory to memoryless nodes
> Date: Mon, 19 Feb 2024 13:10:47 +0900
> 
> With numa balancing on, when a numa system is running where a numa node
> doesn't have its local memory so it has no managed zones, the following
> oops has been observed.  It's because wakeup_kswapd() is called with a
> wrong zone index, -1.  Fixed it by checking the index before calling
> wakeup_kswapd().
> 
> > BUG: unable to handle page fault for address: 00000000000033f3
> > #PF: supervisor read access in kernel mode
> > #PF: error_code(0x0000) - not-present page
> > PGD 0 P4D 0
> > Oops: 0000 [#1] PREEMPT SMP NOPTI
> > CPU: 2 PID: 895 Comm: masim Not tainted 6.6.0-dirty #255
> > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
> >    rel-1.16.0-0-gd239552ce722-prebuilt.qemu.org 04/01/2014
> > RIP: 0010:wakeup_kswapd (./linux/mm/vmscan.c:7812)
> > Code: (omitted)
> > RSP: 0000:ffffc90004257d58 EFLAGS: 00010286
> > RAX: ffffffffffffffff RBX: ffff88883fff0480 RCX: 0000000000000003
> > RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff88883fff0480
> > RBP: ffffffffffffffff R08: ff0003ffffffffff R09: ffffffffffffffff
> > R10: ffff888106c95540 R11: 0000000055555554 R12: 0000000000000003
> > R13: 0000000000000000 R14: 0000000000000000 R15: ffff88883fff0940
> > FS:  00007fc4b8124740(0000) GS:ffff888827c00000(0000) knlGS:0000000000000000
> > CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > CR2: 00000000000033f3 CR3: 000000026cc08004 CR4: 0000000000770ee0
> > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> > PKRU: 55555554
> > Call Trace:
> >  <TASK>
> > ? __die
> > ? page_fault_oops
> > ? __pte_offset_map_lock
> > ? exc_page_fault
> > ? asm_exc_page_fault
> > ? wakeup_kswapd
> > migrate_misplaced_page
> > __handle_mm_fault
> > handle_mm_fault
> > do_user_addr_fault
> > exc_page_fault
> > asm_exc_page_fault
> > RIP: 0033:0x55b897ba0808
> > Code: (omitted)
> > RSP: 002b:00007ffeefa821a0 EFLAGS: 00010287
> > RAX: 000055b89983acd0 RBX: 00007ffeefa823f8 RCX: 000055b89983acd0
> > RDX: 00007fc2f8122010 RSI: 0000000000020000 RDI: 000055b89983acd0
> > RBP: 00007ffeefa821a0 R08: 0000000000000037 R09: 0000000000000075
> > R10: 0000000000000000 R11: 0000000000000202 R12: 0000000000000000
> > R13: 00007ffeefa82410 R14: 000055b897ba5dd8 R15: 00007fc4b8340000
> >  </TASK>
> 
> Fix this by avoiding any attempt to migrate memory to memoryless nodes.
> 
> Link: https://lkml.kernel.org/r/20240219041920.1183-1-byungchul@sk.com
> Link: https://lkml.kernel.org/r/20240216111502.79759-1-byungchul@sk.com
> Fixes: c574bbe917036 ("NUMA balancing: optimize page placement for memory tiering system")
> Signed-off-by: Byungchul Park <byungchul@sk.com>
> Reviewed-by: Oscar Salvador <osalvador@suse.de>
> Reviewed-by: "Huang, Ying" <ying.huang@intel.com>
> Reviewed-by: Phil Auld <pauld@redhat.com>
> Cc: Benjamin Segall <bsegall@google.com>
> Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
> Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Juri Lelli <juri.lelli@redhat.com>
> Cc: Mel Gorman <mgorman@suse.de>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Cc: Valentin Schneider <vschneid@redhat.com>
> Cc: Vincent Guittot <vincent.guittot@linaro.org>
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> ---
> 
>  kernel/sched/fair.c |    6 ++++++
>  1 file changed, 6 insertions(+)
> 
> --- a/kernel/sched/fair.c~sched-numa-mm-do-not-try-to-migrate-memory-to-memoryless-nodes
> +++ a/kernel/sched/fair.c
> @@ -1831,6 +1831,12 @@ bool should_numa_migrate_memory(struct t
>  	int last_cpupid, this_cpupid;
>  
>  	/*
> +	 * Cannot migrate to memoryless nodes.
> +	 */
> +	if (!node_state(dst_nid, N_MEMORY))
> +		return false;
> +
> +	/*
>  	 * The pages in slow memory node should be migrated according
>  	 * to hot/cold instead of private/shared.
>  	 */
> _