Re: [PATCHi v2] mm: put_and_wait_on_page_locked() while page is migrated

From: Joey Pabalinas <joeypabalinas@gmail.com>
To: Hugh Dickins <hughd@google.com>
Cc: Mike Rapoport <rppt@linux.ibm.com>,
	Matthew Wilcox <willy@infradead.org>,
	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, Joey Pabalinas <joeypabalinas@gmail.com>
Subject: Re: [PATCHi v2] mm: put_and_wait_on_page_locked() while page is migrated
Date: Tue, 27 Nov 2018 12:40:52 -1000	[thread overview]
Message-ID: <20181127224052.2zyxkdo4lbecq4cz@gmail.com> (raw)
In-Reply-To: <alpine.LSU.2.11.1811271258070.4506@eggly.anvils>

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On Tue, Nov 27, 2018 at 01:08:50PM -0800, Hugh Dickins wrote:
> 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.

For something which is internal to a single file I strongly prefer
the first as well.

-- 
Cheers,
Joey Pabalinas

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