[Ocfs2-devel] [PATCH v8 02/25] mm: Return void from various readahead functions

Matthew Wilcox
Tue, 25 Feb 2020 21:48:15 -0000

ondemand_readahead has two callers, neither of which use the return value.
That means that both ra_submit and __do_page_cache_readahead() can return
void, and we don't need to worry that a present page in the readahead
window causes us to return a smaller nr_pages than we ought to have.

Similarly, no caller uses the return value from force_page_cache_readahead().

Signed-off-by: Matthew Wilcox (Oracle) <willy at infradead.org>
Reviewed-by: Dave Chinner <dchinner at redhat.com>
Reviewed-by: John Hubbard <jhubbard at nvidia.com>
Reviewed-by: Christoph Hellwig <hch at lst.de>
---
 mm/fadvise.c   |  4 ----
 mm/internal.h  | 12 ++++++------
 mm/readahead.c | 31 +++++++++++++------------------
 3 files changed, 19 insertions(+), 28 deletions(-)

diff --git a/mm/fadvise.c b/mm/fadvise.c
index 3efebfb9952c..0e66f2aaeea3 100644
--- a/mm/fadvise.c
+++ b/mm/fadvise.c
@@ -104,10 +104,6 @@ int generic_fadvise(struct file *file, loff_t offset,
loff_t len, int advice)
 		if (!nrpages)
 			nrpages = ~0UL;

-		/*
-		 * Ignore return value because fadvise() shall return
-		 * success even if filesystem can't retrieve a hint,
-		 */
 		force_page_cache_readahead(mapping, file, start_index, nrpages);
 		break;
 	case POSIX_FADV_NOREUSE:
diff --git a/mm/internal.h b/mm/internal.h
index 83f353e74654..15aaebebd768 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -49,20 +49,20 @@ void unmap_page_range(struct mmu_gather *tlb,
 			     unsigned long addr, unsigned long end,
 			     struct zap_details *details);

-int force_page_cache_readahead(struct address_space *, struct file *,
+void force_page_cache_readahead(struct address_space *, struct file *,
 		pgoff_t index, unsigned long nr_to_read);
-extern unsigned int __do_page_cache_readahead(struct address_space *mapping,
-		struct file *filp, pgoff_t offset, unsigned long nr_to_read,
+void __do_page_cache_readahead(struct address_space *, struct file *,
+		pgoff_t index, unsigned long nr_to_read,
 		unsigned long lookahead_size);

 /*
  * Submit IO for the read-ahead request in file_ra_state.
  */
-static inline unsigned long ra_submit(struct file_ra_state *ra,
+static inline void ra_submit(struct file_ra_state *ra,
 		struct address_space *mapping, struct file *filp)
 {
-	return __do_page_cache_readahead(mapping, filp,
-					ra->start, ra->size, ra->async_size);
+	__do_page_cache_readahead(mapping, filp,
+			ra->start, ra->size, ra->async_size);
 }

 /*
diff --git a/mm/readahead.c b/mm/readahead.c
index 2fe72cd29b47..41a592886da7 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -149,10 +149,8 @@ static int read_pages(struct address_space *mapping, struct
file *filp,
  * the pages first, then submits them for I/O. This avoids the very bad
  * behaviour which would occur if page allocations are causing VM writeback.
  * We really don't want to intermingle reads and writes like that.
- *
- * Returns the number of pages requested, or the maximum amount of I/O allowed.
  */
-unsigned int __do_page_cache_readahead(struct address_space *mapping,
+void __do_page_cache_readahead(struct address_space *mapping,
 		struct file *filp, pgoff_t offset, unsigned long nr_to_read,
 		unsigned long lookahead_size)
 {
@@ -166,7 +164,7 @@ unsigned int __do_page_cache_readahead(struct address_space
*mapping,
 	gfp_t gfp_mask = readahead_gfp_mask(mapping);

 	if (isize == 0)
-		goto out;
+		return;

 	end_index = ((isize - 1) >> PAGE_SHIFT);

@@ -211,23 +209,21 @@ unsigned int __do_page_cache_readahead(struct
address_space *mapping,
 	if (nr_pages)
 		read_pages(mapping, filp, &page_pool, nr_pages, gfp_mask);
 	BUG_ON(!list_empty(&page_pool));
-out:
-	return nr_pages;
 }

 /*
  * Chunk the readahead into 2 megabyte units, so that we don't pin too much
  * memory at once.
  */
-int force_page_cache_readahead(struct address_space *mapping, struct file
*filp,
-			       pgoff_t offset, unsigned long nr_to_read)
+void force_page_cache_readahead(struct address_space *mapping,
+		struct file *filp, pgoff_t offset, unsigned long nr_to_read)
 {
 	struct backing_dev_info *bdi = inode_to_bdi(mapping->host);
 	struct file_ra_state *ra = &filp->f_ra;
 	unsigned long max_pages;

 	if (unlikely(!mapping->a_ops->readpage &&
!mapping->a_ops->readpages))
-		return -EINVAL;
+		return;

 	/*
 	 * If the request exceeds the readahead window, allow the read to
@@ -245,7 +241,6 @@ int force_page_cache_readahead(struct address_space
*mapping, struct file *filp,
 		offset += this_chunk;
 		nr_to_read -= this_chunk;
 	}
-	return 0;
 }

 /*
@@ -378,11 +373,10 @@ static int try_context_readahead(struct address_space
*mapping,
 /*
  * A minimal readahead algorithm for trivial sequential/random reads.
  */
-static unsigned long
-ondemand_readahead(struct address_space *mapping,
-		   struct file_ra_state *ra, struct file *filp,
-		   bool hit_readahead_marker, pgoff_t offset,
-		   unsigned long req_size)
+static void ondemand_readahead(struct address_space *mapping,
+		struct file_ra_state *ra, struct file *filp,
+		bool hit_readahead_marker, pgoff_t offset,
+		unsigned long req_size)
 {
 	struct backing_dev_info *bdi = inode_to_bdi(mapping->host);
 	unsigned long max_pages = ra->ra_pages;
@@ -428,7 +422,7 @@ ondemand_readahead(struct address_space *mapping,
 		rcu_read_unlock();

 		if (!start || start - offset > max_pages)
-			return 0;
+			return;

 		ra->start = start;
 		ra->size = start - offset;	/* old async_size */
@@ -464,7 +458,8 @@ ondemand_readahead(struct address_space *mapping,
 	 * standalone, small random read
 	 * Read as is, and do not pollute the readahead state.
 	 */
-	return __do_page_cache_readahead(mapping, filp, offset, req_size, 0);
+	__do_page_cache_readahead(mapping, filp, offset, req_size, 0);
+	return;

 initial_readahead:
 	ra->start = offset;
@@ -489,7 +484,7 @@ ondemand_readahead(struct address_space *mapping,
 		}
 	}

-	return ra_submit(ra, mapping, filp);
+	ra_submit(ra, mapping, filp);
 }

 /**
--
2.25.0