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From: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
To: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Subject: Re: [PATCH 05/10] vmscan: Synchrounous lumpy reclaim use lock_page() instead trylock_page()
Cc: kosaki.motohiro@jp.fujitsu.com, Mel Gorman <mel@csn.ul.ie>,
        KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>, linux-mm@kvack.org,
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        Minchan Kim <minchan.kim@gmail.com>,
        Wu Fengguang <fengguang.wu@intel.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Dave Chinner <david@fromorbit.com>,
        Chris Mason <chris.mason@oracle.com>, Christoph Hellwig <hch@lst.de>,
        Andrew Morton <akpm@linux-foundation.org>
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> Afaik, detailed rule is,
> 
> o kswapd can call lock_page() because they never take page lock outside vmscan

s/lock_page()/lock_page_nosync()/



> o if try_lock() is successed, we can call lock_page_nosync() against its page after unlock.
>   because the task have gurantee of no lock taken.
> o otherwise, direct reclaimer can't call lock_page(). the task may have a lock already.
> 
> I think.
> 
> 
> >  I did not
> > think of an obvious example of when this would happen. Similarly,
> > deadlock situations with mmap_sem shouldn't happen unless multiple page
> > locks are being taken.
> > 
> > (prepares to feel foolish)
> > 
> > What did I miss?
> 
> 
> 
> 
>