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From: Matthew Wilcox <willy@infradead.org>
To: Dave Chinner <david@fromorbit.com>
Cc: cluster-devel@redhat.com, linux-kernel@vger.kernel.org,
	linux-f2fs-devel@lists.sourceforge.net,
	linux-xfs@vger.kernel.org, linux-mm@kvack.org,
	ocfs2-devel@oss.oracle.com, linux-fsdevel@vger.kernel.org,
	linux-ext4@vger.kernel.org, linux-erofs@lists.ozlabs.org,
	linux-btrfs@vger.kernel.org
Subject: Re: [f2fs-dev] [PATCH 04/12] mm: Add readahead address space operation
Date: Thu, 30 Jan 2020 00:00:13 -0800	[thread overview]
Message-ID: <20200130080013.GK6615@bombadil.infradead.org> (raw)
In-Reply-To: <20200129002456.GH18610@dread.disaster.area>

On Wed, Jan 29, 2020 at 11:24:56AM +1100, Dave Chinner wrote:
> On Fri, Jan 24, 2020 at 05:35:45PM -0800, Matthew Wilcox wrote:
> > From: "Matthew Wilcox (Oracle)" <willy@infradead.org>
> > 
> > This replaces ->readpages with a saner interface:
> >  - Return the number of pages not read instead of an ignored error code.
> >  - Pages are already in the page cache when ->readahead is called.
> >  - Implementation looks up the pages in the page cache instead of
> >    having them passed in a linked list.
> ....
> > diff --git a/mm/readahead.c b/mm/readahead.c
> > index 5a6676640f20..6d65dae6dad0 100644
> > --- a/mm/readahead.c
> > +++ b/mm/readahead.c
> > @@ -121,7 +121,18 @@ static void read_pages(struct address_space *mapping, struct file *filp,
> >  
> >  	blk_start_plug(&plug);
> >  
> > -	if (mapping->a_ops->readpages) {
> > +	if (mapping->a_ops->readahead) {
> > +		unsigned left = mapping->a_ops->readahead(filp, mapping,
> > +				start, nr_pages);
> > +
> > +		while (left) {
> > +			struct page *page = readahead_page(mapping,
> > +					start + nr_pages - left - 1);
> 
> Off by one? start = 2, nr_pages = 2, left = 1, this looks up the
> page at index 2, which is the one we issued IO on, not the one we
> "left behind" which is at index 3.

Yup.  I originally had:

		while (left--) ...

decided that was too confusing and didn't quite complete that thought.


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  reply	other threads:[~2020-01-30  8:00 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-25  1:35 [f2fs-dev] [PATCH 00/12] Change readahead API Matthew Wilcox
2020-01-25  1:35 ` [f2fs-dev] [PATCH 03/12] readahead: Put pages in cache earlier Matthew Wilcox
2020-01-25 19:44   ` Matthew Wilcox
2020-01-25  1:35 ` [f2fs-dev] [PATCH 04/12] mm: Add readahead address space operation Matthew Wilcox
2020-01-25  3:57   ` Randy Dunlap
2020-02-01  0:25     ` Matthew Wilcox
2020-01-29  0:24   ` Dave Chinner
2020-01-30  8:00     ` Matthew Wilcox [this message]
2020-01-25  1:35 ` [f2fs-dev] [PATCH 10/12] f2fs: Convert from readpages to readahead Matthew Wilcox
2020-02-13  4:38 ` [f2fs-dev] [PATCH 00/12] Change readahead API Andrew Morton
2020-02-13 13:43   ` Matthew Wilcox

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