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From: Michal Hocko <mhocko@kernel.org>
To: David Rientjes <rientjes@google.com>
Cc: Christopher Lameter <cl@linux.com>,
	Sachin Sant <sachinp@linux.vnet.ibm.com>,
	Pekka Enberg <penberg@kernel.org>,
	Joonsoo Kim <iamjoonsoo.kim@lge.com>,
	Kirill Tkhai <ktkhai@virtuozzo.com>,
	Linux-Next Mailing List <linux-next@vger.kernel.org>,
	linuxppc-dev@lists.ozlabs.org
Subject: Re: [5.6.0-rc2-next-20200218/powerpc] Boot failure on POWER9
Date: Wed, 26 Feb 2020 21:52:15 +0100	[thread overview]
Message-ID: <20200226205215.GW3771@dhcp22.suse.cz> (raw)
In-Reply-To: <alpine.DEB.2.21.2002261228060.208847@chino.kir.corp.google.com>

On Wed 26-02-20 12:31:56, David Rientjes wrote:
> On Wed, 26 Feb 2020, Michal Hocko wrote:
> 
> > On Wed 26-02-20 18:44:13, Cristopher Lameter wrote:
> > > On Wed, 26 Feb 2020, Michal Hocko wrote:
> > > 
> > > > Besides that kmalloc_node shouldn't really have an implicit GFP_THISNODE
> > > > semantic right? At least I do not see anything like that documented
> > > > anywhere.
> > > 
> > > Kmalloc_node does not support memory policies etc. Only kmalloc does.
> > > kmalloc_node is mostly used by subsystems that have determined the active
> > > nodes and want a targeted allocation on those nodes.
> >  
> > I am sorry but I have hard time to follow your responses here. They open
> > more questions than they answer for me. The primary point here is that
> > kmalloc_node on a memory less node blows up and panics the kernel. I
> > strongly believe this is a bug. We cannot really make all callers of
> > kmalloc_node and co. to be hotplug aware.
> > 
> > Another question is the semantic of kmalloc_node when the node cannot
> > satisfy the request. I have always thought that the allocation would
> > simply fall back to any other node unless __GFP_THISNODE is explicitly
> > specified.
> > 
> 
> Am I right in classifying this as a trade-off between an 
> unlikely(!node_state(nid, N_MEMORY)) directly in kmalloc_node() vs fixing 
> up a caller passing a memoryless nid?

The thing is that any check for node online/populated followed by the
allocation is inherently racy without using memory hotplug locking
around that and I am pretty sure this is a step into a wrong direction.

Is there any problem to initialize slub internal data structures for all
possible nodes? This wouldn't require any checks into hot paths.

-- 
Michal Hocko
SUSE Labs

  reply	other threads:[~2020-02-26 20:52 UTC|newest]

Thread overview: 34+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-18 10:45 [5.6.0-rc2-next-20200218/powerpc] Boot failure on POWER9 Sachin Sant
2020-02-18 10:50 ` Kirill Tkhai
2020-02-18 11:01   ` Kirill Tkhai
2020-02-18 11:35     ` Kirill Tkhai
2020-02-18 11:40     ` Sachin Sant
2020-02-18 11:55       ` Michal Hocko
2020-02-18 14:00         ` Sachin Sant
2020-02-18 14:26           ` Michal Hocko
2020-02-18 15:11             ` Sachin Sant
2020-02-18 15:24               ` Michal Hocko
2020-02-22  3:38                 ` Christopher Lameter
2020-02-24  8:58                   ` Michal Hocko
2020-02-26 18:25                     ` Christopher Lameter
2020-02-26 18:41                       ` Michal Hocko
2020-02-26 18:44                         ` Christopher Lameter
2020-02-26 19:01                           ` Michal Hocko
2020-02-26 20:31                             ` David Rientjes
2020-02-26 20:52                               ` Michal Hocko [this message]
2020-02-26 21:45                         ` Vlastimil Babka
2020-02-26 22:29                           ` Vlastimil Babka
2020-02-27 12:12                             ` Michal Hocko
2020-02-27 16:00                               ` Sachin Sant
2020-02-27 16:16                                 ` Vlastimil Babka
2020-02-27 18:26                                   ` Michal Hocko
2020-03-10 15:01                                     ` Michal Hocko
2020-03-12 12:18                                       ` Michael Ellerman
2020-03-12 16:51                                         ` Sachin Sant
2020-03-13 10:48                                           ` Michael Ellerman
2020-03-13 11:12                                             ` Srikar Dronamraju
2020-03-13 11:35                                               ` Vlastimil Babka
2020-03-14  8:10                                                 ` Sachin Sant
2020-02-27 12:02                           ` Michal Hocko
2020-02-18 11:38   ` Sachin Sant
2020-02-18 11:53     ` Kirill Tkhai

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