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Date: Fri, 17 Aug 2018 18:22:13 -0700
From: Matthew Wilcox <willy@infradead.org>
Subject: Re: [PATCH RFC] mm: don't miss the last page because of round-off
 error
Message-ID: <20180818012213.GA14115@bombadil.infradead.org>
References: <20180817231834.15959-1-guro@fb.com>
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Sender: owner-linux-mm@kvack.org
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To: Roman Gushchin <guro@fb.com>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@fb.com, Andrew Morton <akpm@linux-foundation.org>, Johannes Weiner <hannes@cmpxchg.org>, Michal Hocko <mhocko@kernel.org>, Tejun Heo <tj@kernel.org>, Rik van Riel <riel@surriel.com>, Konstantin Khlebnikov <koct9i@gmail.com>

On Fri, Aug 17, 2018 at 04:18:34PM -0700, Roman Gushchin wrote:
> -			scan = div64_u64(scan * fraction[file],
> -					 denominator);
> +			if (scan > 1)
> +				scan = div64_u64(scan * fraction[file],
> +						 denominator);

Wouldn't we be better off doing a div_round_up?  ie:

	scan = div64_u64(scan * fraction[file] + denominator - 1, denominator);

although i'd rather hide that in a new macro in math64.h than opencode it
here.