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Date:   Tue, 27 Nov 2018 13:08:50 -0800 (PST)
From:   Hugh Dickins <hughd@google.com>
To:     Mike Rapoport <rppt@linux.ibm.com>
cc:     Matthew Wilcox <willy@infradead.org>,
        Hugh Dickins <hughd@google.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Baoquan He <bhe@redhat.com>, Michal Hocko <mhocko@suse.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        Andrea Arcangeli <aarcange@redhat.com>,
        David Hildenbrand <david@redhat.com>,
        Mel Gorman <mgorman@techsingularity.net>,
        David Herrmann <dh.herrmann@gmail.com>,
        Tim Chen <tim.c.chen@linux.intel.com>,
        Kan Liang <kan.liang@intel.com>,
        Andi Kleen <ak@linux.intel.com>,
        Davidlohr Bueso <dave@stgolabs.net>,
        Peter Zijlstra <peterz@infradead.org>,
        Christoph Lameter <cl@linux.com>,
        Nick Piggin <npiggin@gmail.com>, pifang@redhat.com,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCHi v2] mm: put_and_wait_on_page_locked() while page is
 migrated
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On Tue, 27 Nov 2018, Mike Rapoport wrote:
> On Mon, Nov 26, 2018 at 11:27:07AM -0800, Hugh Dickins wrote:
> > 
> > +/*
> > + * A choice of three behaviors for wait_on_page_bit_common():
> > + */
> > +enum behavior {
> > +	EXCLUSIVE,	/* Hold ref to page and take the bit when woken, like
> > +			 * __lock_page() waiting on then setting PG_locked.
> > +			 */
> > +	SHARED,		/* Hold ref to page and check the bit when woken, like
> > +			 * wait_on_page_writeback() waiting on PG_writeback.
> > +			 */
> > +	DROP,		/* Drop ref to page before wait, no check when woken,
> > +			 * like put_and_wait_on_page_locked() on PG_locked.
> > +			 */
> > +};
> 
> Can we please make it:
> 
> /**
>  * enum behavior - a choice of three behaviors for wait_on_page_bit_common()
>  */
> enum behavior {
> 	/**
> 	 * @EXCLUSIVE: Hold ref to page and take the bit when woken,
> 	 * like __lock_page() waiting on then setting %PG_locked.
> 	 */
> 	EXCLUSIVE,
> 	/**
> 	 * @SHARED: Hold ref to page and check the bit when woken,
> 	 * like wait_on_page_writeback() waiting on %PG_writeback.
> 	 */
> 	SHARED,
> 	/**
> 	 * @DROP: Drop ref to page before wait, no check when woken,
> 	 * like put_and_wait_on_page_locked() on %PG_locked.
> 	 */
> 	DROP,
> };

I'm with Matthew, I'd prefer not: the first looks a more readable,
less cluttered comment to me than the second: this is just an arg
to an internal helper in mm/filemap.c, itself not kernel-doc'ed.

But the comment is not there for me: if consensus is that the
second is preferable, then sure, we can change it over.

Hugh