From: Matthew Wilcox <willy@infradead.org>
To: Konstantin Khlebnikov <koct9i@gmail.com>
Cc: Roman Gushchin <guro@fb.com>,
linux-mm@kvack.org,
Linux Kernel Mailing List <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>, Shaohua Li <shli@fb.com>
Subject: Re: [PATCH RFC] mm: don't miss the last page because of round-off error
Date: Tue, 21 Aug 2018 06:35:48 -0700 [thread overview]
Message-ID: <20180821133548.GA10602@bombadil.infradead.org> (raw)
In-Reply-To: <CALYGNiOf_0fR4R747J11JNROO7_FW_9u16Bg09f+CdWPiFwGvw@mail.gmail.com>
On Tue, Aug 21, 2018 at 08:11:44AM +0300, Konstantin Khlebnikov wrote:
> On Sat, Aug 18, 2018 at 4:22 AM, Matthew Wilcox <willy@infradead.org> 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.
>
> All numbers here should be up to nr_pages * 200 and fit into unsigned long.
> I see no reason for u64. If they overflow then u64 wouldn't help either.
Shaohua added the div64 usage initially, adding him to the cc.
> There is macro DIV_ROUND_UP in kernel.h
Indeed there is.
next prev parent reply other threads:[~2018-08-21 13:35 UTC|newest]
Thread overview: 8+ 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
2018-08-18 1:22 ` Matthew Wilcox
2018-08-20 17:19 ` Roman Gushchin
2018-08-21 5:11 ` Konstantin Khlebnikov
2018-08-21 13:35 ` Matthew Wilcox [this message]
2018-08-21 17:15 ` Johannes Weiner
2018-08-22 6:01 ` Konstantin Khlebnikov
2018-08-22 17:50 ` Roman Gushchin
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