From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: "Huang, Ying" <ying.huang@intel.com>
Cc: "Andrew Morton" <akpm@linux-foundation.org>,
"Minchan Kim" <minchan@kernel.org>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
"Hugh Dickins" <hughd@google.com>,
"Johannes Weiner" <hannes@cmpxchg.org>,
"Tim Chen" <tim.c.chen@linux.intel.com>,
"Shaohua Li" <shli@fb.com>,
"Mel Gorman" <mgorman@techsingularity.net>,
"J�r�me 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 -mm] mm, swap: Fix race between swapoff and some swap operations
Date: Mon, 11 Dec 2017 09:04:49 -0800 [thread overview]
Message-ID: <20171211170449.GS7829@linux.vnet.ibm.com> (raw)
In-Reply-To: <87609dvnl0.fsf@yhuang-dev.intel.com>
On Mon, Dec 11, 2017 at 01:30:03PM +0800, Huang, Ying wrote:
> Andrew Morton <akpm@linux-foundation.org> writes:
>
> > On Fri, 08 Dec 2017 16:41:38 +0800 "Huang\, Ying" <ying.huang@intel.com> wrote:
> >
> >> > Why do we need srcu here? Is it enough with rcu like below?
> >> >
> >> > It might have a bug/room to be optimized about performance/naming.
> >> > I just wanted to show my intention.
> >>
> >> Yes. rcu should work too. But if we use rcu, it may need to be called
> >> several times to make sure the swap device under us doesn't go away, for
> >> example, when checking si->max in __swp_swapcount() and
> >> add_swap_count_continuation(). And I found we need rcu to protect swap
> >> cache radix tree array too. So I think it may be better to use one
> >> calling to srcu_read_lock/unlock() instead of multiple callings to
> >> rcu_read_lock/unlock().
> >
> > Or use stop_machine() ;) It's very crude but it sure is simple. Does
> > anyone have a swapoff-intensive workload?
>
> Sorry, I don't know how to solve the problem with stop_machine().
>
> The problem we try to resolved is that, we have a swap entry, but that
> swap entry can become invalid because of swappoff between we check it
> and we use it. So we need to prevent swapoff to be run between checking
> and using.
>
> I don't know how to use stop_machine() in swapoff to wait for all users
> of swap entry to finish. Anyone can help me on this?
You can think of stop_machine() as being sort of like a reader-writer
lock. The readers can be any section of code with preemption disabled,
and the writer is the function passed to stop_machine().
Users running real-time applications on Linux don't tend to like
stop_machine() much, but perhaps it is nevertheless the right tool
for this particular job.
Thanx, Paul
next prev parent reply other threads:[~2017-12-11 17:04 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-12-07 1:14 [PATCH -mm] mm, swap: Fix race between swapoff and some swap operations Huang, Ying
2017-12-08 0:29 ` Andrew Morton
2017-12-08 1:43 ` Minchan Kim
[not found] ` <87po7pg4jt.fsf@yhuang-dev.intel.com>
2017-12-08 8:26 ` Minchan Kim
2017-12-08 8:41 ` Huang, Ying
2017-12-08 9:10 ` Minchan Kim
2017-12-08 12:32 ` Huang, Ying
2017-12-13 7:15 ` Minchan Kim
2017-12-13 8:52 ` Huang, Ying
2017-12-08 22:09 ` Andrew Morton
2017-12-11 5:30 ` Huang, Ying
2017-12-11 17:04 ` Paul E. McKenney [this message]
2017-12-12 1:12 ` Huang, Ying
2017-12-12 17:11 ` Paul E. McKenney
2017-12-13 2:17 ` Huang, Ying
2017-12-13 3:27 ` Paul E. McKenney
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