[v7,05/24] mm: Use readahead_control to pass arguments

Commit Message

Matthew Wilcox Feb. 19, 2020, 9 p.m. UTC

From: "Matthew Wilcox (Oracle)" <[e-mail]>

In this patch, only between __do_page_cache_readahead() and
read_pages(), but it will be extended in upcoming patches.  Also add
the readahead_count() accessor.  The read_pages() function becomes aops
centric, as this makes the most sense by the end of the patchset.

Signed-off-by: Matthew Wilcox (Oracle) <[e-mail]>
Reviewed-by: John Hubbard <[e-mail]>
---
 include/linux/pagemap.h | 17 +++++++++++++++++
 mm/readahead.c          | 34 ++++++++++++++++++++--------------
 2 files changed, 37 insertions(+), 14 deletions(-)

Comments

Christoph Hellwig Feb. 24, 2020, 9:36 p.m. UTC | #1

On Wed, Feb 19, 2020 at 01:00:44PM -0800, Matthew Wilcox wrote:
> @@ -160,9 +164,13 @@ void __do_page_cache_readahead(struct address_space *mapping,
>  	unsigned long end_index;	/* The last page we want to read */
>  	LIST_HEAD(page_pool);
>  	int page_idx;
> -	unsigned int nr_pages = 0;
>  	loff_t isize = i_size_read(inode);
>  	gfp_t gfp_mask = readahead_gfp_mask(mapping);
> +	struct readahead_control rac = {
> +		.mapping = mapping,
> +		.file = filp,
> +		._nr_pages = 0,

There is no real need to initialize fields to zero if we initialize
the structure at all.  And while I'd normally not care that much,
having as few references as possible to the _-prefixed internal
variables helps making clear how internal they are.

Otherwise looks good:

Reviewed-by: Christoph Hellwig <[e-mail]>

Patch

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 24894b9b90c9..55fcea0249e6 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -638,6 +638,23 @@  static inline int add_to_page_cache(struct page *page,
 	return error;
 }
 
+/*
+ * 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 _index;
+	unsigned int _nr_pages;
+};
+
+/* The number of pages in this readahead block */
+static inline unsigned int readahead_count(struct readahead_control *rac)
+{
+	return rac->_nr_pages;
+}
+
 static inline unsigned long dir_pages(struct inode *inode)
 {
 	return (unsigned long)(inode->i_size + PAGE_SIZE - 1) >>
diff --git a/mm/readahead.c b/mm/readahead.c
index 9fcd4e32b62d..6a9d99229bd6 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -113,29 +113,32 @@  int read_cache_pages(struct address_space *mapping, struct list_head *pages,
 
 EXPORT_SYMBOL(read_cache_pages);
 
-static void read_pages(struct address_space *mapping, struct file *filp,
-		struct list_head *pages, unsigned int nr_pages, gfp_t gfp)
+static void read_pages(struct readahead_control *rac, struct list_head *pages,
+		gfp_t gfp)
 {
+	const struct address_space_operations *aops = rac->mapping->a_ops;
 	struct blk_plug plug;
 	unsigned page_idx;
 
-	if (!nr_pages)
+	if (!readahead_count(rac))
 		return;
 
 	blk_start_plug(&plug);
 
-	if (mapping->a_ops->readpages) {
-		mapping->a_ops->readpages(filp, mapping, pages, nr_pages);
+	if (aops->readpages) {
+		aops->readpages(rac->file, rac->mapping, pages,
+				readahead_count(rac));
 		/* Clean up the remaining pages */
 		put_pages_list(pages);
 		goto out;
 	}
 
-	for (page_idx = 0; page_idx < nr_pages; page_idx++) {
+	for (page_idx = 0; page_idx < readahead_count(rac); page_idx++) {
 		struct page *page = lru_to_page(pages);
 		list_del(&page->lru);
-		if (!add_to_page_cache_lru(page, mapping, page->index, gfp))
-			mapping->a_ops->readpage(filp, page);
+		if (!add_to_page_cache_lru(page, rac->mapping, page->index,
+				gfp))
+			aops->readpage(rac->file, page);
 		put_page(page);
 	}
 
@@ -143,6 +146,7 @@  static void read_pages(struct address_space *mapping, struct file *filp,
 	blk_finish_plug(&plug);
 
 	BUG_ON(!list_empty(pages));
+	rac->_nr_pages = 0;
 }
 
 /*
@@ -160,9 +164,13 @@  void __do_page_cache_readahead(struct address_space *mapping,
 	unsigned long end_index;	/* The last page we want to read */
 	LIST_HEAD(page_pool);
 	int page_idx;
-	unsigned int nr_pages = 0;
 	loff_t isize = i_size_read(inode);
 	gfp_t gfp_mask = readahead_gfp_mask(mapping);
+	struct readahead_control rac = {
+		.mapping = mapping,
+		.file = filp,
+		._nr_pages = 0,
+	};
 
 	if (isize == 0)
 		return;
@@ -185,9 +193,7 @@  void __do_page_cache_readahead(struct address_space *mapping,
 			 * contiguous pages before continuing with the next
 			 * batch.
 			 */
-			read_pages(mapping, filp, &page_pool, nr_pages,
-						gfp_mask);
-			nr_pages = 0;
+			read_pages(&rac, &page_pool, gfp_mask);
 			continue;
 		}
 
@@ -198,7 +204,7 @@  void __do_page_cache_readahead(struct address_space *mapping,
 		list_add(&page->lru, &page_pool);
 		if (page_idx == nr_to_read - lookahead_size)
 			SetPageReadahead(page);
-		nr_pages++;
+		rac._nr_pages++;
 	}
 
 	/*
@@ -206,7 +212,7 @@  void __do_page_cache_readahead(struct address_space *mapping,
 	 * uptodate then the caller will launch readpage again, and
 	 * will then handle the error.
 	 */
-	read_pages(mapping, filp, &page_pool, nr_pages, gfp_mask);
+	read_pages(&rac, &page_pool, gfp_mask);
 }
 
 /*