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From: Matthew Wilcox <willy@infradead.org>
To: John Hubbard <jhubbard@nvidia.com>
Cc: linux-fsdevel@vger.kernel.org, linux-mm@kvack.org,
	linux-kernel@vger.kernel.org, linux-btrfs@vger.kernel.org,
	linux-erofs@lists.ozlabs.org, linux-ext4@vger.kernel.org,
	linux-f2fs-devel@lists.sourceforge.net, cluster-devel@redhat.com,
	ocfs2-devel@oss.oracle.com, linux-xfs@vger.kernel.org
Subject: Re: [PATCH v5 04/13] mm: Add readahead address space operation
Date: Fri, 14 Feb 2020 17:15:05 -0800
Message-ID: <20200215011505.GD7778@bombadil.infradead.org> (raw)
In-Reply-To: <755399a8-8fdf-bfac-9f23-81579ff63ddf@nvidia.com>

On Thu, Feb 13, 2020 at 09:36:25PM -0800, John Hubbard wrote:
> > +static inline struct page *readahead_page(struct readahead_control *rac)
> > +{
> > +	struct page *page;
> > +
> > +	if (!rac->nr_pages)
> > +		return NULL;
> > +
> > +	page = xa_load(&rac->mapping->i_pages, rac->start);
> 
> 
> Is it worth asserting that the page was found:
> 
> 	VM_BUG_ON_PAGE(!page || xa_is_value(page), page);
> 
> ? Or is that overkill here?

It shouldn't be possible since they were just added in a locked state.
If it did happen, it'll be caught by the assert below -- dereferencing
a NULL pointer or a shadow entry is not going to go well.

> > +	VM_BUG_ON_PAGE(!PageLocked(page), page);
> > +	rac->batch_count = hpage_nr_pages(page);
> > +	rac->start += rac->batch_count;
> 
> The above was surprising, until I saw the other thread with Dave and you.
> I was reviewing this patchset in order to have a chance at understanding the 
> follow-on patchset ("Large pages in the page cache"), and it seems like that
> feature has a solid head start here. :)  

Right, I'll document that.


  reply index

Thread overview: 31+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-11  1:03 [PATCH v5 00/13] Change readahead API Matthew Wilcox
2020-02-11  1:03 ` [PATCH v5 01/13] mm: Fix the return type of __do_page_cache_readahead Matthew Wilcox
2020-02-11  8:19   ` Johannes Thumshirn
2020-02-11 12:34     ` Matthew Wilcox
2020-02-12 18:13   ` Christoph Hellwig
2020-02-14  3:19   ` John Hubbard
2020-02-14  4:21     ` Matthew Wilcox
2020-02-14  4:33       ` John Hubbard
2020-02-14 19:50   ` Matthew Wilcox
2020-02-11  1:03 ` [PATCH v5 02/13] mm: Ignore return value of ->readpages Matthew Wilcox
2020-02-12 18:13   ` Christoph Hellwig
2020-02-11  1:03 ` [PATCH v5 03/13] mm: Put readahead pages in cache earlier Matthew Wilcox
2020-02-14  3:36   ` John Hubbard
2020-02-15  1:15     ` Matthew Wilcox
2020-02-11  1:03 ` [PATCH v5 04/13] mm: Add readahead address space operation Matthew Wilcox
2020-02-11  4:52   ` Dave Chinner
2020-02-11 12:54     ` Matthew Wilcox
2020-02-11 20:08       ` Dave Chinner
2020-02-12 18:18   ` Christoph Hellwig
2020-02-14  5:36   ` John Hubbard
2020-02-15  1:15     ` Matthew Wilcox [this message]
2020-02-11  1:03 ` [PATCH v5 05/13] mm: Add page_cache_readahead_limit Matthew Wilcox
2020-02-11  1:03 ` [PATCH v5 06/13] fs: Convert mpage_readpages to mpage_readahead Matthew Wilcox
2020-02-13 22:09   ` Junxiao Bi
2020-02-11  1:03 ` [PATCH v5 07/13] btrfs: Convert from readpages to readahead Matthew Wilcox
2020-02-11  1:03 ` [PATCH v5 08/13] erofs: Convert uncompressed files " Matthew Wilcox
2020-02-11  1:03 ` [PATCH v5 09/13] erofs: Convert compressed " Matthew Wilcox
2020-02-11  1:03 ` [PATCH v5 10/13] ext4: Convert " Matthew Wilcox
2020-02-11  1:03 ` [PATCH v5 11/13] f2fs: " Matthew Wilcox
2020-02-11  1:03 ` [PATCH v5 12/13] fuse: " Matthew Wilcox
2020-02-11  1:03 ` [PATCH v5 13/13] iomap: " Matthew Wilcox

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