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Date: Thu, 4 Jan 2018 10:21:14 +0000
From: Mel Gorman <mgorman@techsingularity.net>
To: "Huang, Ying" <ying.huang@intel.com>
Cc: Jan Kara <jack@suse.cz>, Mel Gorman <mgorman@suse.de>,
        Minchan Kim <minchan@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, Hugh Dickins <hughd@google.com>,
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        Rik van Riel <riel@redhat.com>,
        Dave Jiang <dave.jiang@intel.com>,
        Aaron Lu <aaron.lu@intel.com>
Subject: Re: [PATCH -V4 -mm] mm, swap: Fix race between swapoff and some swap
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On Thu, Jan 04, 2018 at 09:17:36AM +0800, Huang, Ying wrote:
> > Maybe, but in this particular case, I would prefer to go with something
> > more conventional unless there is strong evidence that it's an improvement
> > (which I doubt in this case given the cost of migration overall and the
> > corner case of migrating a dirty page).
> 
> So you like page_lock() more than RCU? 

In this instance, yes.

> Is there any problem of RCU?
> The object to be protected isn't clear?
> 

It's not clear what object is being protected or how it's protected and
it's not the usual means a mapping is pinned. Furthermore, in the event
a page is being truncated, we really do not want to bother doing any
migration work for compaction purposes as it's a waste.

-- 
Mel Gorman
SUSE Labs