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From: Andrew Morton <akpm@linux-foundation.org>
To: Andi Kleen <andi.kleen@intel.com>
Cc: Feng Tang <feng.tang@intel.com>, Qian Cai <cai@lca.pw>,
	Dennis Zhou <dennis@kernel.org>, Tejun Heo <tj@kernel.org>,
	Christoph Lameter <cl@linux.com>,
	kernel test robot <rong.a.chen@intel.com>,
	Michal Hocko <mhocko@suse.com>,
	Johannes Weiner <hannes@cmpxchg.org>,
	Matthew Wilcox <willy@infradead.org>,
	Mel Gorman <mgorman@suse.de>, Kees Cook <keescook@chromium.org>,
	Luis Chamberlain <mcgrof@kernel.org>,
	Iurii Zaikin <yzaikin@google.com>,
	tim.c.chen@intel.com, dave.hansen@intel.com,
	ying.huang@intel.com, linux-mm@kvack.org,
	linux-kernel@vger.kernel.org, lkp@lists.01.org
Subject: Re: [mm] 4e2c82a409: ltp.overcommit_memory01.fail
Date: Mon, 6 Jul 2020 16:42:20 -0700
Message-ID: <20200706164220.cc73e53c7f1b285910c82807@linux-foundation.org> (raw)
In-Reply-To: <20200706133434.GA3483883@tassilo.jf.intel.com>

On Mon, 6 Jul 2020 06:34:34 -0700 Andi Kleen <andi.kleen@intel.com> wrote:

> >  	ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
> > -	if (ret == 0 && write)
> > +	if (ret == 0 && write) {
> > +		if (sysctl_overcommit_memory == OVERCOMMIT_NEVER)
> > +			schedule_on_each_cpu(sync_overcommit_as);
> 
> The schedule_on_each_cpu is not atomic, so the problem could still happen
> in that window.
> 
> I think it may be ok if it eventually resolves, but certainly needs
> a comment explaining it.

It sure does.

The new exported-to-everything percpu_counter_sync() should have full
formal documentation as well, please.

> Can you do some stress testing toggling the
> policy all the time on different CPUs and running the test on
> other CPUs and see if the test fails?
> 
> The other alternative would be to define some intermediate state
> for the sysctl variable and only switch to never once the schedule_on_each_cpu
> returned. But that's more complexity.
> 
> 
> -Andi

  reply index

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-21  7:36 [PATCH v5 0/3] make vm_committed_as_batch aware of vm overcommit policy Feng Tang
2020-06-21  7:36 ` [PATCH v5 1/3] proc/meminfo: avoid open coded reading of vm_committed_as Feng Tang
2020-06-21  7:36 ` [PATCH v5 2/3] mm/util.c: make vm_memory_committed() more accurate Feng Tang
2020-06-21  7:36 ` [PATCH v5 3/3] mm: adjust vm_committed_as_batch according to vm overcommit policy Feng Tang
2020-06-22 13:25   ` [mm] 4e2c82a409: will-it-scale.per_process_ops 1894.6% improvement kernel test robot
     [not found]   ` <20200702063201.GG3874@shao2-debian>
2020-07-02  7:12     ` [mm] 4e2c82a409: ltp.overcommit_memory01.fail Feng Tang
2020-07-05  3:20       ` Qian Cai
2020-07-05  4:44       ` Feng Tang
2020-07-05 12:15         ` Qian Cai
2020-07-05 12:58           ` Feng Tang
2020-07-05 15:52             ` Qian Cai
2020-07-06  1:43               ` Feng Tang
2020-07-06  2:36                 ` Qian Cai
2020-07-06 13:24                   ` Feng Tang
2020-07-06 13:34                     ` Andi Kleen
2020-07-06 23:42                       ` Andrew Morton [this message]
2020-07-07  2:38                       ` Feng Tang
2020-07-07  4:00                         ` Huang, Ying
2020-07-07  5:41                           ` Feng Tang
2020-07-09  4:55                             ` Feng Tang
2020-07-09 13:40                               ` Qian Cai
2020-07-09 14:15                                 ` Feng Tang
2020-07-10  1:38                                   ` Feng Tang
2020-07-10  3:26                                     ` Qian Cai
2020-07-07  1:06                     ` Dennis Zhou
2020-07-07  3:24                       ` Feng Tang
2020-07-07 10:28               ` Michal Hocko
2020-06-24  9:45 ` [PATCH v5 0/3] make vm_committed_as_batch aware of vm overcommit policy Michal Hocko
2020-07-07 11:43 [mm] 4e2c82a409: ltp.overcommit_memory01.fail Qian Cai
2020-07-07 12:06 ` Michal Hocko
2020-07-07 13:04   ` Qian Cai
2020-07-07 13:56     ` Michal Hocko

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