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

Matthew Wilcox
2020-02-25T21:51:21Z

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@infradead.org>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: John Hubbard <jhubbard@nvidia.com>
Reviewed-by: Christoph Hellwig <hch@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