Re: [PATCH v5 04/13] mm: Add readahead address space operation

Dave Chinner
2020-02-11T04:52:39Z

On Mon, Feb 10, 2020 at 05:03:39PM -0800, Matthew Wilcox wrote:
> From: "Matthew Wilcox (Oracle)" <willy@infradead.org>
>
> This replaces ->readpages with a saner interface:
> - Return void 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.
>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>

....

>
> +/*
> + * Readahead is of a block of consecutive pages.
> + */
> +struct readahead_control {
> + struct file *file;
> + struct address_space *mapping;
> +/* private: use the readahead_* accessors instead */
> + pgoff_t start;
> + unsigned int nr_pages;
> + unsigned int batch_count;
> +};
> +
> +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);
> + VM_BUG_ON_PAGE(!PageLocked(page), page);
> + rac->batch_count = hpage_nr_pages(page);
> + rac->start += rac->batch_count;

There's no mention of large page support in the patch description
and I don't recall this sort of large page batching in previous
iterations.

This seems like new functionality to me, not directly related to
the initial ->readahead API change? What have I missed?

Cheers,

Dave.
--
Dave Chinner
david@fromorbit.com