From: Feng Tang <feng.tang@intel.com>
To: Andi Kleen <andi.kleen@intel.com>
Cc: Qian Cai <cai@lca.pw>, Michal Hocko <mhocko@suse.com>,
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: Sat, 30 May 2020 00:04:01 +0800 [thread overview]
Message-ID: <20200529160401.GJ93879@shbuild999.sh.intel.com> (raw)
In-Reply-To: <20200529155025.GC621576@tassilo.jf.intel.com>
On Fri, May 29, 2020 at 08:50:25AM -0700, Andi Kleen 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 is not atomic.
> There's still a race window here over all the CPUs where the WARN_ON could
> happen because you change the global first.
The re-computing of batch number comes after this sync, so at this
point the batch is still the bigger one, and won't trigger the warning.
> Probably you would need another global that says "i'm currently changing
> the mode" and then skip the WARN_ON in that window. Maybe a sequence lock.
>
> Seems all overkill to me. Better to kill the warning.
Yes, the cost is high, schedule_on_each_cpu is labeled as "very slow"
in the code comments.
Thanks,
Feng
>
> -Andi
next prev parent reply other threads:[~2020-05-29 16:04 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-08 7:25 [PATCH 0/3] make vm_committed_as_batch aware of vm overcommit policy 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
2020-05-29 15:50 ` Andi Kleen
2020-05-29 16:04 ` Feng Tang [this message]
2020-05-28 15:48 ` Michal Hocko
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