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Date: Mon, 26 Nov 2018 20:53:45 +0100
From: Michal Hocko <mhocko@kernel.org>
Subject: Re: [PATCHi v2] mm: put_and_wait_on_page_locked() while page is
 migrated
Message-ID: <20181126195345.GI12455@dhcp22.suse.cz>
References: <alpine.LSU.2.11.1811241858540.4415@eggly.anvils>
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To: Hugh Dickins <hughd@google.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>, Andrew Morton <akpm@linux-foundation.org>, Baoquan He <bhe@redhat.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

On Mon 26-11-18 11:27:07, Hugh Dickins wrote:
[...]
> @@ -1049,25 +1056,44 @@ static void wake_up_page(struct page *page, int bit)
>  	wake_up_page_bit(page, bit);
>  }
>  
> +/*
> + * 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.
> +			 */
> +};

I like this. It makes to semantic much more clear.

Thanks!
-- 
Michal Hocko
SUSE Labs