From mboxrd@z Thu Jan  1 00:00:00 1970
From: Matthew Wilcox <willy@infradead.org>
Date: Wed, 19 Feb 2020 06:41:17 -0800
Subject: [Cluster-devel] [PATCH v6 07/19] mm: Put readahead pages in
	cache earlier
In-Reply-To: <e3671faa-dfb3-ceba-3120-a445b2982a95@nvidia.com>
References: <20200217184613.19668-1-willy@infradead.org>
	<20200217184613.19668-12-willy@infradead.org>
	<e3671faa-dfb3-ceba-3120-a445b2982a95@nvidia.com>
Message-ID: <20200219144117.GP24185@bombadil.infradead.org>
List-Id: <cluster-devel.redhat.com>
To: cluster-devel.redhat.com
MIME-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 7bit

On Tue, Feb 18, 2020 at 04:01:43PM -0800, John Hubbard wrote:
> How about this instead? It uses the "for" loop fully and more naturally,
> and is easier to read. And it does the same thing:
> 
> 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);
> 
> 	return page;
> }
> 
> static inline struct page *readahead_next(struct readahead_control *rac)
> {
> 	rac->_nr_pages -= rac->_batch_count;
> 	rac->_start += rac->_batch_count;
> 
> 	return readahead_page(rac);
> }
> 
> #define readahead_for_each(rac, page)			\
> 	for (page = readahead_page(rac); page != NULL;	\
> 	     page = readahead_page(rac))

I'll go you one better ... how about we do this instead:

static inline struct page *readahead_page(struct readahead_control *rac)
{
        struct page *page;

        BUG_ON(rac->_batch_count > rac->_nr_pages);
        rac->_nr_pages -= rac->_batch_count;
        rac->_index += rac->_batch_count;
        rac->_batch_count = 0;

        if (!rac->_nr_pages)
                return NULL;

        page = xa_load(&rac->mapping->i_pages, rac->_index);
        VM_BUG_ON_PAGE(!PageLocked(page), page);
        rac->_batch_count = hpage_nr_pages(page);

        return page;
}

#define readahead_for_each(rac, page)                                   \
        while ((page = readahead_page(rac)))

No more readahead_next() to forget to add to filesystems which don't use
the readahead_for_each() iterator.  Ahem.