linux-kernel - Re: [PATCH v2 02/28] mm: Add functions to zero portions of a folio

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Date:   Wed, 17 Nov 2021 14:07:00 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     "Darrick J. Wong" <djwong@...nel.org>
Cc:     linux-xfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-block@...r.kernel.org,
        Jens Axboe <axboe@...nel.dk>,
        Christoph Hellwig <hch@...radead.org>
Subject: Re: [PATCH v2 02/28] mm: Add functions to zero portions of a folio

On Tue, Nov 16, 2021 at 08:45:27PM -0800, Darrick J. Wong wrote:
> > +/**
> > + * folio_zero_segment() - Zero a byte range in a folio.
> > + * @folio: The folio to write to.
> > + * @start: The first byte to zero.
> > + * @end: One more than the last byte in the first range.
> > + */
> > +static inline void folio_zero_segment(struct folio *folio,
> > +		size_t start, size_t end)
> > +{
> > +	zero_user_segments(&folio->page, start, end, 0, 0);
> > +}
> > +
> > +/**
> > + * folio_zero_range() - Zero a byte range in a folio.
> > + * @folio: The folio to write to.
> > + * @start: The first byte to zero.
> > + * @length: The number of bytes to zero.
> > + */
> > +static inline void folio_zero_range(struct folio *folio,
> > +		size_t start, size_t length)
> > +{
> > +	zero_user_segments(&folio->page, start, start + length, 0, 0);
> 
> At first I thought "Gee, this is wrong, end should be start+length-1!"
> 
> Then I looked at zero_user_segments and realized that despite the
> parameter name "endi1", it really wants you to tell it the next byte.
> Not the end byte of the range you want to zero.
> 
> Then I looked at the other two new functions and saw that you documented
> this, and now I get why Linus ranted about this some time ago.
> 
> The code looks right, but the "end" names rankle me.  Can we please
> change them all?  Or at least in the new functions, if you all already
> fought a flamewar over this that I'm not aware of?

Change them to what?  I tend to use 'end' to mean 'excluded end' and
'max' to mean 'included end'.  What would you call the excluded end?