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Subject: [RFC PATCH 2/7] mm: Make ondemand_readahead() take a
 readahead_control struct
From:   David Howells <dhowells@redhat.com>
To:     willy@infradead.org
Cc:     dhowells@redhat.com, linux-fsdevel@vger.kernel.org,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org
Date:   Tue, 01 Sep 2020 17:28:29 +0100
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Make ondemand_readahead() take a readahead_control struct in preparation
for making do_sync_mmap_readahead() pass down an RAC struct.

Signed-off-by: David Howells <dhowells@redhat.com>
---

 mm/readahead.c |   35 +++++++++++++++++++++--------------
 1 file changed, 21 insertions(+), 14 deletions(-)

diff --git a/mm/readahead.c b/mm/readahead.c
index 91859e6e2b7d..0e16fb4809f5 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -511,14 +511,15 @@ static bool page_cache_readahead_order(struct readahead_control *rac,
 /*
  * A minimal readahead algorithm for trivial sequential/random reads.
  */
-static void ondemand_readahead(struct address_space *mapping,
-		struct file_ra_state *ra, struct file *file,
-		struct page *page, pgoff_t index, unsigned long req_size)
+static void ondemand_readahead(struct readahead_control *rac,
+			       struct file_ra_state *ra,
+			       struct page *page)
 {
-	DEFINE_READAHEAD(rac, file, mapping, index);
-	struct backing_dev_info *bdi = inode_to_bdi(mapping->host);
+	struct backing_dev_info *bdi = inode_to_bdi(rac->mapping->host);
 	unsigned long max_pages = ra->ra_pages;
 	unsigned long add_pages;
+	unsigned long req_size = rac->_nr_pages;
+	unsigned long index = rac->_index;
 	pgoff_t prev_index;
 
 	/*
@@ -556,7 +557,7 @@ static void ondemand_readahead(struct address_space *mapping,
 		pgoff_t start;
 
 		rcu_read_lock();
-		start = page_cache_next_miss(mapping, index + 1, max_pages);
+		start = page_cache_next_miss(rac->mapping, index + 1, max_pages);
 		rcu_read_unlock();
 
 		if (!start || start - index > max_pages)
@@ -589,14 +590,14 @@ static void ondemand_readahead(struct address_space *mapping,
 	 * Query the page cache and look for the traces(cached history pages)
 	 * that a sequential stream would leave behind.
 	 */
-	if (try_context_readahead(mapping, ra, index, req_size, max_pages))
+	if (try_context_readahead(rac->mapping, ra, index, req_size, max_pages))
 		goto readit;
 
 	/*
 	 * standalone, small random read
 	 * Read as is, and do not pollute the readahead state.
 	 */
-	__do_page_cache_readahead(&rac, req_size, 0);
+	__do_page_cache_readahead(rac, req_size, 0);
 	return;
 
 initial_readahead:
@@ -622,10 +623,10 @@ static void ondemand_readahead(struct address_space *mapping,
 		}
 	}
 
-	rac._index = ra->start;
-	if (page && page_cache_readahead_order(&rac, ra, thp_order(page)))
+	rac->_index = ra->start;
+	if (page && page_cache_readahead_order(rac, ra, thp_order(page)))
 		return;
-	__do_page_cache_readahead(&rac, ra->size, ra->async_size);
+	__do_page_cache_readahead(rac, ra->size, ra->async_size);
 }
 
 /**
@@ -645,6 +646,9 @@ void page_cache_sync_readahead(struct address_space *mapping,
 			       struct file_ra_state *ra, struct file *filp,
 			       pgoff_t index, unsigned long req_count)
 {
+	DEFINE_READAHEAD(rac, filp, mapping, index);
+	rac._nr_pages = req_count;
+
 	/* no read-ahead */
 	if (!ra->ra_pages)
 		return;
@@ -659,7 +663,7 @@ void page_cache_sync_readahead(struct address_space *mapping,
 	}
 
 	/* do read-ahead */
-	ondemand_readahead(mapping, ra, filp, NULL, index, req_count);
+	ondemand_readahead(&rac, ra, NULL);
 }
 EXPORT_SYMBOL_GPL(page_cache_sync_readahead);
 
@@ -683,7 +687,10 @@ page_cache_async_readahead(struct address_space *mapping,
 			   struct page *page, pgoff_t index,
 			   unsigned long req_count)
 {
-	/* no read-ahead */
+	DEFINE_READAHEAD(rac, filp, mapping, index);
+	rac._nr_pages = req_count;
+
+	/* No Read-ahead */
 	if (!ra->ra_pages)
 		return;
 
@@ -705,7 +712,7 @@ page_cache_async_readahead(struct address_space *mapping,
 		return;
 
 	/* do read-ahead */
-	ondemand_readahead(mapping, ra, filp, page, index, req_count);
+	ondemand_readahead(&rac, ra, page);
 }
 EXPORT_SYMBOL_GPL(page_cache_async_readahead);