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From: Roman Gushchin <guro@fb.com>
To: Matthew Wilcox <willy@infradead.org>
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>
Subject: Re: [PATCH RFC] mm: don't miss the last page because of round-off error
Date: Mon, 20 Aug 2018 10:19:01 -0700	[thread overview]
Message-ID: <20180820171855.GA3993@tower.DHCP.thefacebook.com> (raw)
In-Reply-To: <20180818012213.GA14115@bombadil.infradead.org>

On Fri, Aug 17, 2018 at 06:22:13PM -0700, Matthew Wilcox wrote:
> 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.

Good idea! Will do in v2.

Thanks!

WARNING: multiple messages have this Message-ID (diff)
From: Roman Gushchin <guro@fb.com>
To: Matthew Wilcox <willy@infradead.org>
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>
Subject: Re: [PATCH RFC] mm: don't miss the last page because of round-off error
Date: Mon, 20 Aug 2018 10:19:01 -0700	[thread overview]
Message-ID: <20180820171855.GA3993@tower.DHCP.thefacebook.com> (raw)
In-Reply-To: <20180818012213.GA14115@bombadil.infradead.org>

On Fri, Aug 17, 2018 at 06:22:13PM -0700, Matthew Wilcox wrote:
> 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.

Good idea! Will do in v2.

Thanks!

  reply	other threads:[~2018-08-20 17:19 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-08-17 23:18 [PATCH RFC] mm: don't miss the last page because of round-off error Roman Gushchin
2018-08-17 23:18 ` Roman Gushchin
2018-08-18  1:22 ` Matthew Wilcox
2018-08-20 17:19   ` Roman Gushchin [this message]
2018-08-20 17:19     ` Roman Gushchin
2018-08-21  5:11   ` Konstantin Khlebnikov
2018-08-21 13:35     ` Matthew Wilcox
2018-08-21 17:15     ` Johannes Weiner
2018-08-22  6:01       ` Konstantin Khlebnikov
2018-08-22 17:50         ` Roman Gushchin
2018-08-22 17:50           ` Roman Gushchin

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