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Message-ID: <20150602121442.GD26425@suse.de>
Date: Tue, 2 Jun 2015 13:14:42 +0100
From: Mel Gorman <mgorman@...e.de>
To: Jeff Layton <jeff.layton@...marydata.com>
Cc: Jerome Marchand <jmarchan@...hat.com>,
Jeff Layton <jlayton@...marydata.com>,
'Linux-MM' <linux-mm@...ck.org>,
'linux-kernel' <linux-kernel@...r.kernel.org>
Subject: Re: swap: nfs: Sleeping function called from an rcu read section in
nfs_swap_activate
On Thu, May 28, 2015 at 07:24:34AM -0400, Jeff Layton wrote:
> > > 1) this is not done under a lock, so the non-atomic ++/-- is racy if
> > > there are multiple swapons/swapoffs running concurrently on the same
> > > xprt. Shouldn't those use an atomic?
> > >
> >
> > It would be more appropriate to use atomics. It's a long time ago but I
> > doubt I considered the possibility of multiple swapons racing at the
> > time of implementation. Activation is typically a serialised task run
> > from init.
> >
> > > 2) on enable, "swapper" is incremented and memalloc is set on the
> > > socket. Do we need to do xs_set_memalloc every time swapon is called,
> > > or only on a 0->1 swapper transition.
> > >
> >
> > Every time because the static_key_slow_inc call is for the total number
> > of connections.
> >
>
> That still seems wrong. The static_key would still be active even if
> you just did it once per xprt.
>
True. As long as it is active while one swapfile exists then it's good.
--
Mel Gorman
SUSE Labs
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