linux-kernel - [PATCH v5 3/5] mm/readahead: Make space in struct file_ra

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Message-ID: <20250609092729.274960-4-ryan.roberts@arm.com>
Date: Mon,  9 Jun 2025 10:27:25 +0100
From: Ryan Roberts <ryan.roberts@....com>
To: Andrew Morton <akpm@...ux-foundation.org>,
	"Matthew Wilcox (Oracle)" <willy@...radead.org>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Christian Brauner <brauner@...nel.org>,
	Jan Kara <jack@...e.cz>,
	David Hildenbrand <david@...hat.com>,
	Dave Chinner <david@...morbit.com>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>,
	Kalesh Singh <kaleshsingh@...gle.com>,
	Zi Yan <ziy@...dia.com>
Cc: Ryan Roberts <ryan.roberts@....com>,
	linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org,
	linux-mm@...ck.org
Subject: [PATCH v5 3/5] mm/readahead: Make space in struct file_ra_state

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.

Acked-by: David Hildenbrand <david@...hat.com>
Reviewed-by: Jan Kara <jack@...e.cz>
Signed-off-by: Ryan Roberts <ryan.roberts@....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 05abdabe9db7..87e7d5790e43 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1052,7 +1052,7 @@ 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 a6459874bb2a..7bb4ffca8487 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -3217,7 +3217,7 @@ 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 */
@@ -3285,7 +3285,7 @@ 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)
@@ -3605,7 +3605,7 @@ 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);
@@ -3667,7 +3667,7 @@ 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;
@@ -3709,7 +3709,8 @@ 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