[RFC PATCH v4 3/5] mm/readahead: Make space in struct file_ra_state

[Ryan Roberts <ryan.roberts@arm.com>]

We need to be able to store the preferred folio order associated with a
readahead request in the struct file_ra_state so that we can more
accurately increase the order across subsequent readahead requests. But
struct file_ra_state is per-struct file, so we don't really want to
increase it's size.

mmap_miss is currently 32 bits but it is only counted up to 10 *
MMAP_LOTSAMISS, which is currently defined as 1000. So 16 bits should be
plenty. Redefine it to unsigned short, making room for order as unsigned
short in follow up commit.

Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
---
 include/linux/fs.h |  2 +-
 mm/filemap.c       | 11 ++++++-----
 2 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 016b0fe1536e..44362bef0010 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1042,7 +1042,7 @@ struct file_ra_state {
 	unsigned int size;
 	unsigned int async_size;
 	unsigned int ra_pages;
-	unsigned int mmap_miss;
+	unsigned short mmap_miss;
 	loff_t prev_pos;
 };
 
diff --git a/mm/filemap.c b/mm/filemap.c
index 7b90cbeb4a1a..fa129ecfd80f 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -3207,7 +3207,7 @@ static struct file *do_sync_mmap_readahead(struct vm_fault *vmf)
 	DEFINE_READAHEAD(ractl, file, ra, mapping, vmf->pgoff);
 	struct file *fpin = NULL;
 	unsigned long vm_flags = vmf->vma->vm_flags;
-	unsigned int mmap_miss;
+	unsigned short mmap_miss;
 
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 	/* Use the readahead code, even if readahead is disabled */
@@ -3275,7 +3275,7 @@ static struct file *do_async_mmap_readahead(struct vm_fault *vmf,
 	struct file_ra_state *ra = &file->f_ra;
 	DEFINE_READAHEAD(ractl, file, ra, file->f_mapping, vmf->pgoff);
 	struct file *fpin = NULL;
-	unsigned int mmap_miss;
+	unsigned short mmap_miss;
 
 	/* If we don't want any read-ahead, don't bother */
 	if (vmf->vma->vm_flags & VM_RAND_READ || !ra->ra_pages)
@@ -3595,7 +3595,7 @@ static struct folio *next_uptodate_folio(struct xa_state *xas,
 static vm_fault_t filemap_map_folio_range(struct vm_fault *vmf,
 			struct folio *folio, unsigned long start,
 			unsigned long addr, unsigned int nr_pages,
-			unsigned long *rss, unsigned int *mmap_miss)
+			unsigned long *rss, unsigned short *mmap_miss)
 {
 	vm_fault_t ret = 0;
 	struct page *page = folio_page(folio, start);
@@ -3657,7 +3657,7 @@ static vm_fault_t filemap_map_folio_range(struct vm_fault *vmf,
 
 static vm_fault_t filemap_map_order0_folio(struct vm_fault *vmf,
 		struct folio *folio, unsigned long addr,
-		unsigned long *rss, unsigned int *mmap_miss)
+		unsigned long *rss, unsigned short *mmap_miss)
 {
 	vm_fault_t ret = 0;
 	struct page *page = &folio->page;
@@ -3699,7 +3699,8 @@ vm_fault_t filemap_map_pages(struct vm_fault *vmf,
 	struct folio *folio;
 	vm_fault_t ret = 0;
 	unsigned long rss = 0;
-	unsigned int nr_pages = 0, mmap_miss = 0, mmap_miss_saved, folio_type;
+	unsigned int nr_pages = 0, folio_type;
+	unsigned short mmap_miss = 0, mmap_miss_saved;
 
 	rcu_read_lock();
 	folio = next_uptodate_folio(&xas, mapping, end_pgoff);
-- 
2.43.0