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Date:   Fri, 8 Dec 2017 14:09:09 -0800
From:   Andrew Morton <>
To:     "Huang\, Ying" <>
Cc:     Minchan Kim <>,
        "Paul E. McKenney" <>,
        <>, <>,
        Hugh Dickins <>,
        "Johannes Weiner" <>,
        Tim Chen <>,
        Shaohua Li <>,
        Mel Gorman <>,
        J�r�me Glisse <>,
        Michal Hocko <>,
        Andrea Arcangeli <>,
        David Rientjes <>,
        Rik van Riel <>, Jan Kara <>,
        Dave Jiang <>,
        Aaron Lu <>
Subject: Re: [PATCH -mm] mm, swap: Fix race between swapoff and some swap

On Fri, 08 Dec 2017 16:41:38 +0800 "Huang\, Ying" <> 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?

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