[PATCH v6 01/19] mm: Return void from various readahead functions

Matthew Wilcox
2020-02-17T18:46:51Z

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

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.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
mm/internal.h | 8 ++++----
mm/readahead.c | 24 ++++++++++--------------
2 files changed, 14 insertions(+), 18 deletions(-)

diff --git a/mm/internal.h b/mm/internal.h
index 3cf20ab3ca01..f779f058118b 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -49,18 +49,18 @@ void unmap_page_range(struct mmu_gather *tlb,
unsigned long addr, unsigned long end,
struct zap_details *details);

-extern unsigned int __do_page_cache_readahead(struct address_space *mapping,
+extern void __do_page_cache_readahead(struct address_space *mapping,
struct file *filp, pgoff_t offset, 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..8ce46d69e6ae 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);

@@ -211,8 +209,6 @@ 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;
}

/*
@@ -378,11 +374,10 @@ 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 +423,7 @@ 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 +459,8 @@ 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 +485,7 @@ ondemand_readahead(struct address_space *mapping,
}
}

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

/**
--
2.25.0