From: "Huang\, Ying" <ying.huang@intel.com>
To: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
Hugh Dickins <hughd@google.com>, Minchan Kim <minchan@kernel.org>,
Johannes Weiner <hannes@cmpxchg.org>,
Tim Chen <tim.c.chen@linux.intel.com>, Shaohua Li <shli@fb.com>,
Mel Gorman <mgorman@techsingularity.net>,
Jerome Glisse <jglisse@redhat.com>,
Michal Hocko <mhocko@suse.com>,
Andrea Arcangeli <aarcange@redhat.com>,
David Rientjes <rientjes@google.com>,
Rik van Riel <riel@redhat.com>, Jan Kara <jack@suse.cz>,
Dave Jiang <dave.jiang@intel.com>, Aaron Lu <aaron.lu@intel.com>
Subject: Re: [PATCH -V3 -mm] mm, swap: Fix race between swapoff and some swap operations
Date: Tue, 19 Dec 2017 09:57:21 +0800 [thread overview]
Message-ID: <877etjv5ry.fsf@yhuang-dev.intel.com> (raw)
In-Reply-To: <20171218230945.GX7829@linux.vnet.ibm.com> (Paul E. McKenney's message of "Mon, 18 Dec 2017 15:09:45 -0800")
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com> writes:
> On Mon, Dec 18, 2017 at 03:41:41PM +0800, Huang, Ying wrote:
>> "Huang, Ying" <ying.huang@intel.com> writes:
>> And, it appears that if we replace smp_wmb() in _enable_swap_info() with
>> stop_machine() in some way, we can avoid smp_rmb() in get_swap_device().
>> This can reduce overhead in normal path further. Can we get same effect
>> with RCU? For example, use synchronize_rcu() instead of stop_machine()?
>>
>> Hi, Paul, can you help me on this?
>
> If the key loads before and after the smp_rmb() are within the same
> RCU read-side critical section, -and- if one of the critical writes is
> before the synchronize_rcu() and the other critical write is after the
> synchronize_rcu(), then you normally don't need the smp_rmb().
>
> Otherwise, you likely do still need the smp_rmb().
My question may be too general, let make it more specific. For the
following program,
"
int a;
int b;
void intialize(void)
{
a = 1;
synchronize_rcu();
b = 2;
}
void test(void)
{
int c;
rcu_read_lock();
c = b;
/* ignored smp_rmb() */
if (c)
pr_info("a=%d\n", a);
rcu_read_unlock();
}
"
Is it possible for it to show
"
a=0
"
in kernel log?
If it couldn't, this could be a useful usage model of RCU to accelerate
hot path.
Best Regards,
Huang, Ying
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next prev parent reply other threads:[~2017-12-19 1:57 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-12-18 7:34 [PATCH -V3 -mm] mm, swap: Fix race between swapoff and some swap operations Huang, Ying
2017-12-18 7:41 ` Huang, Ying
2017-12-18 21:13 ` Junaid Shahid
2017-12-18 23:09 ` Paul E. McKenney
2017-12-19 1:57 ` Huang, Ying [this message]
2017-12-19 5:36 ` Paul E. McKenney
2017-12-19 8:08 ` Huang, Ying
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