linux-kernel - Re: [Xen-devel] [PATCH] drivers/block/xen-blkback/common.h: use DIV_ROUND_UP instead of reimplementing its function

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Message-ID: <20180912091639.oynlvdo6pghnqfvt@mac.bytemobile.com>
Date:   Wed, 12 Sep 2018 11:16:39 +0200
From:   Roger Pau Monné <roger.pau@...rix.com>
To:     Julien Grall <julien.grall@....com>
CC:     Jan Beulich <JBeulich@...e.com>, Jens Axboe <axboe@...nel.dk>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        <linux-kernel@...r.kernel.org>, <linux-block@...r.kernel.org>,
        xen-devel <xen-devel@...ts.xenproject.org>,
        zhong jiang <zhongjiang@...wei.com>
Subject: Re: [Xen-devel] [PATCH] drivers/block/xen-blkback/common.h: use
 DIV_ROUND_UP instead of reimplementing its function

Sorry, I've failed to add Julien in my previous reply.

On Wed, Sep 12, 2018 at 11:13:50AM +0200, Roger Pau Monné wrote:
> Adding Julien how did the work to support XEN_PAGE_SIZE != PAGE_SIZE.
> 
> On Wed, Sep 12, 2018 at 02:14:26AM -0600, Jan Beulich wrote:
> > >>> On 12.09.18 at 07:45, <zhongjiang@...wei.com> wrote:
> > > --- a/drivers/block/xen-blkback/common.h
> > > +++ b/drivers/block/xen-blkback/common.h
> > > @@ -65,7 +65,7 @@
> > >  	(XEN_PAGES_PER_INDIRECT_FRAME / XEN_PAGES_PER_SEGMENT)
> > >  
> > >  #define MAX_INDIRECT_PAGES \
> > > -	((MAX_INDIRECT_SEGMENTS + SEGS_PER_INDIRECT_FRAME - 1)/SEGS_PER_INDIRECT_FRAME)
> > > +		DIV_ROUND_UP(MAX_INDIRECT_SEGMENTS, SEGS_PER_INDIRECT_FRAME)
> > >  #define INDIRECT_PAGES(_segs) DIV_ROUND_UP(_segs, XEN_PAGES_PER_INDIRECT_FRAME)
> > 
> > My first reaction was to suggest
> > 
> > #define MAX_INDIRECT_PAGES INDIRECT_PAGES(MAX_INDIRECT_SEGMENTS)
> > 
> > but that wouldn't match what's there currently (note the two different
> > divisors). I can't really decide whether that's just unfortunate naming
> > of the two macros, or an actual bug.
> 
> I think there's indeed a bug here.
> 
> AFAICT, MAX_INDIRECT_PAGES should use XEN_PAGES_PER_INDIRECT_FRAME and
> then it could be changed as Jan suggested.
> 
> Current MAX_INDIRECT_PAGES is misnamed and should instead be
> MAX_INDIRECT_SEGS (which on x86 is exactly the same because PAGE_SIZE
> == XEN_PAGE_SIZE).
> 
> Roger.
> 
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@...ts.xenproject.org
> https://lists.xenproject.org/mailman/listinfo/xen-devel

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