[PATCH v6 03/19] mm: Use readahead_control to pass arguments

Matthew Wilcox
2020-02-17T18:48:53Z

From: "Matthew Wilcox (Oracle)" <willy@infradead.org>

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.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
include/linux/pagemap.h | 17 +++++++++++++++++
mm/readahead.c | 36 +++++++++++++++++++++---------------
2 files changed, 38 insertions(+), 15 deletions(-)

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index ccb14b6a16b5..982ecda2d4a2 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -630,6 +630,23 @@ 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 _start;
+ 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 12d13b7792da..15329309231f 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -113,26 +113,29 @@ 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;

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);
}

@@ -155,9 +158,13 @@ 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;
@@ -180,10 +187,9 @@ void __do_page_cache_readahead(struct address_space *mapping,
* contiguous pages before continuing with the next
* batch.
*/
- if (nr_pages)
- read_pages(mapping, filp, &page_pool, nr_pages,
- gfp_mask);
- nr_pages = 0;
+ if (readahead_count(&rac))
+ read_pages(&rac, &page_pool, gfp_mask);
+ rac._nr_pages = 0;
continue;
}

@@ -194,7 +200,7 @@ 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++;
}

/*
@@ -202,8 +208,8 @@ void __do_page_cache_readahead(struct address_space *mapping,
* uptodate then the caller will launch readpage again, and
* will then handle the error.
*/
- if (nr_pages)
- read_pages(mapping, filp, &page_pool, nr_pages, gfp_mask);
+ if (readahead_count(&rac))
+ read_pages(&rac, &page_pool, gfp_mask);
BUG_ON(!list_empty(&page_pool));
}

--
2.25.0