[PATCH 5/5] iomap: support RWF_UNCACHED for buffered writes

Jens Axboe
2019-12-12T19:01:50Z

This adds support for RWF_UNCACHED for file systems using iomap to
perform buffered writes. We use the generic infrastructure for this,
by tracking pages we created and calling write_drop_cached_pages()
to issue writeback and prune those pages.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
fs/iomap/apply.c | 24 ++++++++++++++++++++++++
fs/iomap/buffered-io.c | 23 +++++++++++++++++++----
include/linux/iomap.h | 5 +++++
3 files changed, 48 insertions(+), 4 deletions(-)

diff --git a/fs/iomap/apply.c b/fs/iomap/apply.c
index e76148db03b8..11b6812f7b37 100644
--- a/fs/iomap/apply.c
+++ b/fs/iomap/apply.c
@@ -92,5 +92,29 @@ iomap_apply(struct iomap_data *data, const struct iomap_ops *ops,
data->flags, &iomap);
}

+ if (written && (data->flags & IOMAP_UNCACHED)) {
+ struct address_space *mapping = data->inode->i_mapping;
+
+ end = data->pos + written;
+ ret = filemap_write_and_wait_range(mapping, data->pos, end);
+ if (ret)
+ goto out;
+
+ /*
+ * No pages were created for this range, we're done
+ */
+ if (!(iomap.flags & IOMAP_F_PAGE_CREATE))
+ goto out;
+
+ /*
+ * Try to invalidate cache pages for the range we just wrote.
+ * We don't care if invalidation fails as the write has still
+ * worked and leaving clean uptodate pages in the page cache
+ * isn't a corruption vector for uncached IO.
+ */
+ invalidate_inode_pages2_range(mapping,
+ data->pos >> PAGE_SHIFT, end >> PAGE_SHIFT);
+ }
+out:
return written ? written : ret;
}
diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index 0a1a195ed1cc..df9d6002858e 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -659,6 +659,7 @@ iomap_write_begin(struct inode *inode, loff_t pos, unsigned len, unsigned flags,
struct page **pagep, struct iomap *iomap, struct iomap *srcmap)
{
const struct iomap_page_ops *page_ops = iomap->page_ops;
+ unsigned aop_flags;
struct page *page;
int status = 0;

@@ -675,8 +676,11 @@ iomap_write_begin(struct inode *inode, loff_t pos, unsigned len, unsigned flags,
return status;
}

+ aop_flags = AOP_FLAG_NOFS;
+ if (flags & IOMAP_UNCACHED)
+ aop_flags |= AOP_FLAG_UNCACHED;
page = grab_cache_page_write_begin(inode->i_mapping, pos >> PAGE_SHIFT,
- AOP_FLAG_NOFS);
+ aop_flags);
if (!page) {
status = -ENOMEM;
goto out_no_page;
@@ -818,6 +822,7 @@ iomap_write_actor(const struct iomap_data *data, struct iomap *iomap,
{
struct inode *inode = data->inode;
struct iov_iter *i = data->priv;
+ unsigned flags = data->flags;
loff_t length = data->len;
loff_t pos = data->pos;
long status = 0;
@@ -851,10 +856,17 @@ iomap_write_actor(const struct iomap_data *data, struct iomap *iomap,
break;
}

- status = iomap_write_begin(inode, pos, bytes, 0, &page, iomap,
- srcmap);
- if (unlikely(status))
+retry:
+ status = iomap_write_begin(inode, pos, bytes, flags,
+ &page, iomap, srcmap);
+ if (unlikely(status)) {
+ if (status == -ENOMEM && (flags & IOMAP_UNCACHED)) {
+ iomap->flags |= IOMAP_F_PAGE_CREATE;
+ flags &= ~IOMAP_UNCACHED;
+ goto retry;
+ }
break;
+ }

if (mapping_writably_mapped(inode->i_mapping))
flush_dcache_page(page);
@@ -907,6 +919,9 @@ iomap_file_buffered_write(struct kiocb *iocb, struct iov_iter *iter,
};
loff_t ret = 0, written = 0;

+ if (iocb->ki_flags & IOCB_UNCACHED)
+ data.flags |= IOMAP_UNCACHED;
+
while (iov_iter_count(iter)) {
data.len = iov_iter_count(iter);
ret = iomap_apply(&data, ops, iomap_write_actor);
diff --git a/include/linux/iomap.h b/include/linux/iomap.h
index 30f40145a9e9..30bb248e1d0d 100644
--- a/include/linux/iomap.h
+++ b/include/linux/iomap.h
@@ -48,12 +48,16 @@ struct vm_fault;
*
* IOMAP_F_BUFFER_HEAD indicates that the file system requires the use of
* buffer heads for this mapping.
+ *
+ * IOMAP_F_PAGE_CREATE indicates that pages had to be allocated to satisfy
+ * this operation.
*/
#define IOMAP_F_NEW 0x01
#define IOMAP_F_DIRTY 0x02
#define IOMAP_F_SHARED 0x04
#define IOMAP_F_MERGED 0x08
#define IOMAP_F_BUFFER_HEAD 0x10
+#define IOMAP_F_PAGE_CREATE 0x20

/*
* Flags set by the core iomap code during operations:
@@ -121,6 +125,7 @@ struct iomap_page_ops {
#define IOMAP_FAULT (1 << 3) /* mapping for page fault */
#define IOMAP_DIRECT (1 << 4) /* direct I/O */
#define IOMAP_NOWAIT (1 << 5) /* do not block */
+#define IOMAP_UNCACHED (1 << 6)

struct iomap_ops {
/*
--
2.24.1