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From: Feng Tang <feng.tang@intel.com>
To: "Kleen, Andi" <andi.kleen@intel.com>, Qian Cai <cai@lca.pw>,
	Michal Hocko <mhocko@suse.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Johannes Weiner <hannes@cmpxchg.org>,
	Stephen Rothwell <sfr@canb.auug.org.au>,
	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>,
	"Chen, Tim C" <tim.c.chen@intel.com>,
	"Hansen, Dave" <dave.hansen@intel.com>,
	"Huang, Ying" <ying.huang@intel.com>,
	"linux-mm@kvack.org" <linux-mm@kvack.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 0/3] make vm_committed_as_batch aware of vm overcommit policy
Date: Fri, 29 May 2020 23:43:15 +0800
Message-ID: <20200529154315.GI93879@shbuild999.sh.intel.com> (raw)
In-Reply-To: <E8ECBC65D0B2554DAD44EBE43059B3741A2BFEEC@ORSMSX110.amr.corp.intel.com>

On Thu, May 28, 2020 at 11:21:36PM +0800, Kleen, Andi wrote:
> 
> 
> >If it's true, then there could be 2 solutions, one is to skip the WARN_ONCE as it has no practical value, as the real >check is the following code, the other is to rectify the percpu counter when the policy is changing to >OVERCOMMIT_NEVER.
> 
> I think it's better to fix it up when the policy changes. That's the right place. The WARN_ON might be useful to catch other bugs.

If we keep the WARN_ON, then the draft fix patch I can think of looks like:

diff --git a/lib/percpu_counter.c b/lib/percpu_counter.c
index a66595b..02d87fc 100644
--- a/lib/percpu_counter.c
+++ b/lib/percpu_counter.c
@@ -98,6 +98,20 @@ void percpu_counter_add_batch(struct percpu_counter *fbc, s64 amount, s32 batch)
 }
 EXPORT_SYMBOL(percpu_counter_add_batch);
 
+void percpu_counter_sync(struct percpu_counter *fbc)
+{
+	unsigned long flags;
+	s64 count;
+
+	raw_spin_lock_irqsave(&fbc->lock, flags);
+	count = __this_cpu_read(*fbc->counters);
+	fbc->count += count;
+	__this_cpu_sub(*fbc->counters, count);
+	raw_spin_unlock_irqrestore(&fbc->lock, flags);
+}
+EXPORT_SYMBOL(percpu_counter_sync);
+
+
 /*
  * Add up all the per-cpu counts, return the result.  This is a more accurate
  * but much slower version of percpu_counter_read_positive()
diff --git a/mm/util.c b/mm/util.c
index 580d268..24322da 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -746,14 +746,24 @@ int overcommit_ratio_handler(struct ctl_table *table, int write, void *buffer,
 	return ret;
 }
 
+static  void sync_overcommit_as(struct work_struct *dummy)
+{
+	percpu_counter_sync(&vm_committed_as);
+}
+
 int overcommit_policy_handler(struct ctl_table *table, int write, void *buffer,
 		size_t *lenp, loff_t *ppos)
 {
 	int ret;
 
 	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);
+
 		mm_compute_batch();
+	}
 
 	return ret;
 }

Any comments?

Thanks,
Feng

> -Andi
>  

  reply index

Thread overview: 34+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-08  7:25 Feng Tang
2020-05-08  7:25 ` [PATCH 1/3] proc/meminfo: avoid open coded reading of vm_committed_as Feng Tang
2020-05-15  7:22   ` Michal Hocko
2020-05-08  7:25 ` [PATCH 2/3] mm/util.c: make vm_memory_committed() more accurate Feng Tang
2020-05-15  7:23   ` Michal Hocko
2020-05-15  8:11     ` Feng Tang
2020-05-15  9:04       ` Michal Hocko
2020-05-15 13:01         ` Feng Tang
2020-05-08  7:25 ` [PATCH 3/3] mm: adjust vm_committed_as_batch according to vm overcommit policy Feng Tang
2020-05-08 11:24   ` Matthew Wilcox
2020-05-08 12:33     ` Feng Tang
2020-05-15  7:41   ` Michal Hocko
2020-05-15  8:02     ` Feng Tang
2020-05-15  9:08       ` Michal Hocko
2020-05-15 11:26         ` Feng Tang
2020-05-15  7:44   ` Michal Hocko
2020-05-15  8:38     ` Feng Tang
2020-05-21 21:27 ` [PATCH 0/3] make vm_committed_as_batch aware of " Qian Cai
2020-05-26 18:14   ` Qian Cai
2020-05-27  1:14     ` Andi Kleen
2020-05-27  1:43       ` Feng Tang
2020-05-27  1:46     ` Feng Tang
2020-05-27  2:25       ` Qian Cai
2020-05-27 10:46         ` Feng Tang
2020-05-27 12:05           ` Qian Cai
2020-05-27 13:33             ` Feng Tang
2020-05-27 15:42               ` Qian Cai
2020-05-28 14:18           ` Qian Cai
2020-05-28 15:10             ` Feng Tang
2020-05-28 15:21               ` Kleen, Andi
2020-05-29 15:43                 ` Feng Tang [this message]
2020-05-29 15:50                   ` Andi Kleen
2020-05-29 16:04                     ` Feng Tang
2020-05-28 15:48               ` Michal Hocko

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