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Subject: [RFC PATCH 3/7] mm: Push readahead_control down into
 force_page_cache_readahead()
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 17:28:37 +0100
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Push readahead_control down into force_page_cache_readahead() from its
callers in preparation for making do_sync_mmap_readahead() pass down an RAC
struct.

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

 mm/fadvise.c   |    6 +++++-
 mm/internal.h  |    3 +--
 mm/readahead.c |   20 ++++++++++++--------
 3 files changed, 18 insertions(+), 11 deletions(-)

diff --git a/mm/fadvise.c b/mm/fadvise.c
index 0e66f2aaeea3..b68d2f2959d5 100644
--- a/mm/fadvise.c
+++ b/mm/fadvise.c
@@ -104,7 +104,11 @@ int generic_fadvise(struct file *file, loff_t offset, loff_t len, int advice)
 		if (!nrpages)
 			nrpages = ~0UL;
 
-		force_page_cache_readahead(mapping, file, start_index, nrpages);
+		{
+			DEFINE_READAHEAD(rac, file, mapping, start_index);
+			rac._nr_pages = nrpages;
+			force_page_cache_readahead(&rac);
+		}
 		break;
 	case POSIX_FADV_NOREUSE:
 		break;
diff --git a/mm/internal.h b/mm/internal.h
index bf2bee6c42a1..2eb9f7f5f134 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -49,8 +49,7 @@ void unmap_page_range(struct mmu_gather *tlb,
 			     unsigned long addr, unsigned long end,
 			     struct zap_details *details);
 
-void force_page_cache_readahead(struct address_space *, struct file *,
-		pgoff_t index, unsigned long nr_to_read);
+void force_page_cache_readahead(struct readahead_control *);
 void __do_page_cache_readahead(struct readahead_control *,
 		unsigned long nr_to_read, unsigned long lookahead_size);
 
diff --git a/mm/readahead.c b/mm/readahead.c
index 0e16fb4809f5..e557c6d5a183 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -271,13 +271,12 @@ void __do_page_cache_readahead(struct readahead_control *rac,
  * Chunk the readahead into 2 megabyte units, so that we don't pin too much
  * memory at once.
  */
-void force_page_cache_readahead(struct address_space *mapping,
-		struct file *file, pgoff_t index, unsigned long nr_to_read)
+void force_page_cache_readahead(struct readahead_control *rac)
 {
-	DEFINE_READAHEAD(rac, file, mapping, index);
+	struct address_space *mapping = rac->mapping;
 	struct backing_dev_info *bdi = inode_to_bdi(mapping->host);
-	struct file_ra_state *ra = &file->f_ra;
-	unsigned long max_pages;
+	struct file_ra_state *ra = &rac->file->f_ra;
+	unsigned long max_pages, index, nr_to_read;
 
 	if (unlikely(!mapping->a_ops->readpage && !mapping->a_ops->readpages &&
 			!mapping->a_ops->readahead))
@@ -287,14 +286,19 @@ void force_page_cache_readahead(struct address_space *mapping,
 	 * If the request exceeds the readahead window, allow the read to
 	 * be up to the optimal hardware IO size
 	 */
+	index = readahead_index(rac);
 	max_pages = max_t(unsigned long, bdi->io_pages, ra->ra_pages);
-	nr_to_read = min(nr_to_read, max_pages);
+	nr_to_read = min_t(unsigned long, readahead_count(rac), max_pages);
 	while (nr_to_read) {
 		unsigned long this_chunk = (2 * 1024 * 1024) / PAGE_SIZE;
 
 		if (this_chunk > nr_to_read)
 			this_chunk = nr_to_read;
-		__do_page_cache_readahead(&rac, this_chunk, 0);
+
+		rac->_index = index;
+		rac->_nr_pages = this_chunk;
+		// Do I need to modify rac->_batch_count?
+		__do_page_cache_readahead(rac, this_chunk, 0);
 
 		index += this_chunk;
 		nr_to_read -= this_chunk;
@@ -658,7 +662,7 @@ void page_cache_sync_readahead(struct address_space *mapping,
 
 	/* be dumb */
 	if (filp && (filp->f_mode & FMODE_RANDOM)) {
-		force_page_cache_readahead(mapping, filp, index, req_count);
+		force_page_cache_readahead(&rac);
 		return;
 	}