linux-kernel - Re: [PATCH 18/21] iomap: Convert iomap_add_to

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Message-ID: <YYNUoONKjuo6Izfz@casper.infradead.org>
Date:   Thu, 4 Nov 2021 03:33:52 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     "Darrick J. Wong" <djwong@...nel.org>, 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>
Subject: Re: [PATCH 18/21] iomap: Convert iomap_add_to_ioend to take a folio

On Wed, Nov 03, 2021 at 08:54:50AM -0700, Christoph Hellwig wrote:
> > -	 * Walk through the page to find areas to write back. If we run off the
> > -	 * end of the current map or find the current map invalid, grab a new
> > -	 * one.
> > +	 * Walk through the folio to find areas to write back. If we
> > +	 * run off the end of the current map or find the current map
> > +	 * invalid, grab a new one.
> 
> No real need for reflowing the comment, it still fits just fine even
> with the folio change.

Sure, but I don't like using column 79, unless it's better to.  We're on
three lines anyway; may as well make better use of that third line.

> > +	isize = i_size_read(inode);
> > +	end_pos = page_offset(page) + PAGE_SIZE;
> > +	if (end_pos - 1 >= isize) {
> 
> Wouldn't this check be more obvious as:
> 
> 	if (end_pos > i_size) {

I _think_ we restrict the maximum file size to 2^63 - 1 to avoid i_size
ever being negative.  But that means that end_pos might be 2^63 (ie
LONG_MIN), so we need to subtract one from it to get the right answer.
Maybe worth a comment?