LKML Archive on lore.kernel.org
 help / color / Atom feed
From: Feng Tang <feng.tang@intel.com>
To: Qian Cai <cai@lca.pw>
Cc: "Huang, Ying" <ying.huang@intel.com>,
	Andi Kleen <andi.kleen@intel.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Michal Hocko <mhocko@suse.com>, Dennis Zhou <dennis@kernel.org>,
	Tejun Heo <tj@kernel.org>, Christoph Lameter <cl@linux.com>,
	kernel test robot <rong.a.chen@intel.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, linux-mm@kvack.org,
	linux-kernel@vger.kernel.org, lkp@lists.01.org
Subject: Re: [mm] 4e2c82a409: ltp.overcommit_memory01.fail
Date: Thu, 9 Jul 2020 22:15:19 +0800
Message-ID: <20200709141519.GA81727@shbuild999.sh.intel.com> (raw)
In-Reply-To: <20200709134040.GA1110@lca.pw>

Hi Qian Cai,

On Thu, Jul 09, 2020 at 09:40:40AM -0400, Qian Cai wrote:
> > > > Can we change the batch firstly, then sync the global counter, finally
> > > > change the overcommit policy?
> > > 
> > > These reorderings are really head scratching :)
> > > 
> > > I've thought about this before when Qian Cai first reported the warning
> > > message, as kernel had a check: 
> > > 
> > > 	VM_WARN_ONCE(percpu_counter_read(&vm_committed_as) <
> > > 			-(s64)vm_committed_as_batch * num_online_cpus(),
> > > 			"memory commitment underflow");
> > > 
> > > If the batch is decreased first, the warning will be easier/earlier to be
> > > triggered, so I didn't brought this up when handling the warning message.
> > > 
> > > But it might work now, as the warning has been removed.
> > 
> > I tested the reorder way, and the test could pass in 100 times run. The
> > new order when changing policy to OVERCOMMIT_NEVER:
> >   1. re-compute the batch ( to the smaller one)
> >   2. do the on_each_cpu sync
> >   3. really change the policy to NEVER.
> > 
> > It solves one of previous concern, that after the sync is done on cpuX,
> > but before the whole sync on all cpus are done, there is a window that
> > the percpu-counter could be enlarged again.
> > 
> > IIRC Andi had concern about read side cost when doing the sync, my
> > understanding is most of the readers (malloc/free/map/unmap) are using
> > percpu_counter_read_positive, which is a fast path without involving lock.
> > 
> > As for the problem itself, I agree with Michal's point, that usually there
> > is no normal case that will change the overcommit_policy too frequently.
> > 
> > The code logic is mainly in overcommit_policy_handler(), based on the
> > previous sync fix. please help to review, thanks!
> > 
> > int overcommit_policy_handler(struct ctl_table *table, int write, void *buffer,
> > 		size_t *lenp, loff_t *ppos)
> > {
> > 	int ret;
> > 
> > 	if (write) {
> > 		int new_policy;
> > 		struct ctl_table t;
> > 
> > 		t = *table;
> > 		t.data = &new_policy;
> > 		ret = proc_dointvec_minmax(&t, write, buffer, lenp, ppos);
> > 		if (ret)
> > 			return ret;
> > 
> > 		mm_compute_batch(new_policy);
> > 		if (new_policy == OVERCOMMIT_NEVER)
> > 			schedule_on_each_cpu(sync_overcommit_as);
> > 		sysctl_overcommit_memory = new_policy;
> > 	} else {
> > 		ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
> > 	}
> > 
> > 	return ret;
> > }
> 
> Rather than having to indent those many lines, how about this?

Thanks for the cleanup suggestion.

> t = *table;
> t.data = &new_policy;

The input table->data is actually &sysctl_overcommit_memory, so
there is a problem for "read" case, it will return the 'new_policy'
value instead of real sysctl_overcommit_memory.

It should work after adding a check
	if (write)
		t.data = &new_policy;

> ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
			    --> &t

Thanks,
Feng
	
> if (ret || !write)
> 	return ret;
> mm_compute_batch(new_policy);
> if (new_policy == OVERCOMMIT_NEVER)
> 	schedule_on_each_cpu(sync_overcommit_as);
> 
> sysctl_overcommit_memory = new_policy;
> return ret;

  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
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 [this message]
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

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20200709141519.GA81727@shbuild999.sh.intel.com \
    --to=feng.tang@intel.com \
    --cc=akpm@linux-foundation.org \
    --cc=andi.kleen@intel.com \
    --cc=cai@lca.pw \
    --cc=cl@linux.com \
    --cc=dave.hansen@intel.com \
    --cc=dennis@kernel.org \
    --cc=hannes@cmpxchg.org \
    --cc=keescook@chromium.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-mm@kvack.org \
    --cc=lkp@lists.01.org \
    --cc=mcgrof@kernel.org \
    --cc=mgorman@suse.de \
    --cc=mhocko@suse.com \
    --cc=rong.a.chen@intel.com \
    --cc=tim.c.chen@intel.com \
    --cc=tj@kernel.org \
    --cc=willy@infradead.org \
    --cc=ying.huang@intel.com \
    --cc=yzaikin@google.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

LKML Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/lkml/0 lkml/git/0.git
	git clone --mirror https://lore.kernel.org/lkml/1 lkml/git/1.git
	git clone --mirror https://lore.kernel.org/lkml/2 lkml/git/2.git
	git clone --mirror https://lore.kernel.org/lkml/3 lkml/git/3.git
	git clone --mirror https://lore.kernel.org/lkml/4 lkml/git/4.git
	git clone --mirror https://lore.kernel.org/lkml/5 lkml/git/5.git
	git clone --mirror https://lore.kernel.org/lkml/6 lkml/git/6.git
	git clone --mirror https://lore.kernel.org/lkml/7 lkml/git/7.git
	git clone --mirror https://lore.kernel.org/lkml/8 lkml/git/8.git
	git clone --mirror https://lore.kernel.org/lkml/9 lkml/git/9.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 lkml lkml/ https://lore.kernel.org/lkml \
		linux-kernel@vger.kernel.org
	public-inbox-index lkml

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-kernel


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git