linux-kernel - Re: [PATCH v3] scatterlist: add sg_alloc_table_from

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Message-Id: <20120522131059.415a881c.akpm@linux-foundation.org>
Date:	Tue, 22 May 2012 13:10:59 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Tomasz Stanislawski <t.stanislaws@...sung.com>
Cc:	paul.gortmaker@...driver.com,
	'박경민' 
	<kyungmin.park@...sung.com>, amwang@...hat.com,
	dri-devel@...ts.freedesktop.org,
	"'???/Mobile S/W Platform Lab.(???)/E3(??)/????'" 
	<inki.dae@...sung.com>, prashanth.g@...sung.com,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	"linux-media@...r.kernel.org" <linux-media@...r.kernel.org>,
	Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	Rob Clark <rob@...com>, Dave Airlie <airlied@...hat.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Andy Whitcroft <apw@...dowen.org>,
	Johannes Weiner <hannes@...xchg.org>
Subject: Re: [PATCH v3] scatterlist: add sg_alloc_table_from_pages function

On Mon, 21 May 2012 16:01:50 +0200
Tomasz Stanislawski <t.stanislaws@...sung.com> wrote:

> >> +int sg_alloc_table_from_pages(struct sg_table *sgt,
> >> +	struct page **pages, unsigned int n_pages,
> >> +	unsigned long offset, unsigned long size,
> >> +	gfp_t gfp_mask)
> > 
> > I guess a 32-bit n_pages is OK.  A 16TB IO seems enough ;)
> > 
> 
> Do you think that 'unsigned long' for offset is too big?
> 
> Ad n_pages. Assuming that Moore's law holds it will take
> circa 25 years before the limit of 16 TB is reached :) for
> high-end scatterlist operations.
> Or I can change the type of n_pages to 'unsigned long' now at
> no cost :).

By then it will be Someone Else's Problem ;)

> >> +{
> >> +	unsigned int chunks;
> >> +	unsigned int i;
> > 
> > erk, please choose a different name for this.  When a C programmer sees
> > "i", he very much assumes it has type "int".  Making it unsigned causes
> > surprise.
> > 
> > And don't rename it to "u"!  Let's give it a nice meaningful name.  pageno?
> > 
> 
> The problem is that 'i' is  a natural name for a loop counter.

It's also the natural name for an integer.  If a C programmer sees "i",
he thinks "int".  It's a Fortran thing ;)

> AFAIK, in the kernel code developers try to avoid Hungarian notation.
> A name of a variable should reflect its purpose, not its type.
> I can change the name of 'i' to 'pageno' and 'j' to 'pageno2' (?)
> but I think it will make the code less reliable.

Well, one could do something radical such as using "p".


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