iomap: add support for sub-pagesize buffered I/O without buffer heads
After already supporting a simple implementation of buffered writes for
the blocksize == PAGE_SIZE case in the last commit this adds full support
even for smaller block sizes. There are three bits of per-block
information in the buffer_head structure that really matter for the iomap
read and write path:
- uptodate status (BH_uptodate)
- marked as currently under read I/O (BH_Async_Read)
- marked as currently under write I/O (BH_Async_Write)
Instead of having new per-block structures this now adds a per-page
structure called struct iomap_page to track this information in a slightly
different form:
- a bitmap for the per-block uptodate status. For worst case of a 64k
page size system this bitmap needs to contain 128 bits. For the
typical 4k page size case it only needs 8 bits, although we still
need a full unsigned long due to the way the atomic bitmap API works.
- two atomic_t counters are used to track the outstanding read and write
counts
There is quite a bit of boilerplate code as the buffered I/O path uses
various helper methods, but the actual code is very straight forward.
Signed-off-by: Christoph Hellwig <[email protected]>
Reviewed-by: Brian Foster <[email protected]>
Reviewed-by: Darrick J. Wong <[email protected]>
Signed-off-by: Darrick J. Wong <[email protected]>
diff --git a/include/linux/iomap.h b/include/linux/iomap.h
index 5eb9ca8..3555d54 100644
--- a/include/linux/iomap.h
+++ b/include/linux/iomap.h
@@ -2,6 +2,9 @@
#ifndef LINUX_IOMAP_H
#define LINUX_IOMAP_H 1
+#include <linux/atomic.h>
+#include <linux/bitmap.h>
+#include <linux/mm.h>
#include <linux/types.h>
struct address_space;
@@ -98,12 +101,40 @@ struct iomap_ops {
ssize_t written, unsigned flags, struct iomap *iomap);
};
+/*
+ * Structure allocate for each page when block size < PAGE_SIZE to track
+ * sub-page uptodate status and I/O completions.
+ */
+struct iomap_page {
+ atomic_t read_count;
+ atomic_t write_count;
+ DECLARE_BITMAP(uptodate, PAGE_SIZE / 512);
+};
+
+static inline struct iomap_page *to_iomap_page(struct page *page)
+{
+ if (page_has_private(page))
+ return (struct iomap_page *)page_private(page);
+ return NULL;
+}
+
ssize_t iomap_file_buffered_write(struct kiocb *iocb, struct iov_iter *from,
const struct iomap_ops *ops);
int iomap_readpage(struct page *page, const struct iomap_ops *ops);
int iomap_readpages(struct address_space *mapping, struct list_head *pages,
unsigned nr_pages, const struct iomap_ops *ops);
int iomap_set_page_dirty(struct page *page);
+int iomap_is_partially_uptodate(struct page *page, unsigned long from,
+ unsigned long count);
+int iomap_releasepage(struct page *page, gfp_t gfp_mask);
+void iomap_invalidatepage(struct page *page, unsigned int offset,
+ unsigned int len);
+#ifdef CONFIG_MIGRATION
+int iomap_migrate_page(struct address_space *mapping, struct page *newpage,
+ struct page *page, enum migrate_mode mode);
+#else
+#define iomap_migrate_page NULL
+#endif
int iomap_file_dirty(struct inode *inode, loff_t pos, loff_t len,
const struct iomap_ops *ops);
int iomap_zero_range(struct inode *inode, loff_t pos, loff_t len,
