[v1,5/6] bio: add a helper calculating nr segments to alloc

Commit Message

Pavel Begunkov Dec. 15, 2020, 12:20 a.m. UTC

A preparation patch. It adds a simple helper which abstracts out number
of segments we're allocating for a bio from iov_iter_npages().

Signed-off-by: Pavel Begunkov <[e-mail]>
---
 fs/block_dev.c       | 7 ++++---
 fs/iomap/direct-io.c | 9 ++++-----
 include/linux/bio.h  | 6 ++++++
 3 files changed, 14 insertions(+), 8 deletions(-)

Comments

Dave Chinner Dec. 15, 2020, 1 a.m. UTC | #1

On Tue, Dec 15, 2020 at 12:20:24AM +0000, Pavel Begunkov wrote:
> A preparation patch. It adds a simple helper which abstracts out number
> of segments we're allocating for a bio from iov_iter_npages().

Preparation for what? bio_iov_vecs_to_alloc() doesn't seem to be
used outside this specific patch, so it's not clear what it's
actually needed for...

Cheers,

Dave.

Pavel Begunkov Dec. 15, 2020, 1:07 a.m. UTC | #2

On 15/12/2020 01:00, Dave Chinner wrote:
> On Tue, Dec 15, 2020 at 12:20:24AM +0000, Pavel Begunkov wrote:
>> A preparation patch. It adds a simple helper which abstracts out number
>> of segments we're allocating for a bio from iov_iter_npages().
> 
> Preparation for what? bio_iov_vecs_to_alloc() doesn't seem to be
> used outside this specific patch, so it's not clear what it's
> actually needed for...

Yes, it's not used, but modified in [6/6]. It's here to generilise
these bits of iomap and block dio, so we can change the behaviour in
one place.

Dave Chinner Dec. 15, 2020, 1:09 a.m. UTC | #3

On Tue, Dec 15, 2020 at 12:00:23PM +1100, Dave Chinner wrote:
> On Tue, Dec 15, 2020 at 12:20:24AM +0000, Pavel Begunkov wrote:
> > A preparation patch. It adds a simple helper which abstracts out number
> > of segments we're allocating for a bio from iov_iter_npages().
> 
> Preparation for what? bio_iov_vecs_to_alloc() doesn't seem to be
> used outside this specific patch, so it's not clear what it's
> actually needed for...

Never mind, I'm just blind.

Cheers,

Dave.

Christoph Hellwig Dec. 22, 2020, 2:07 p.m. UTC | #4

The new helper needs a comment explaining the use case.

Otherwise looks good:

Reviewed-by: Christoph Hellwig <[e-mail]>

Patch

diff --git a/fs/block_dev.c b/fs/block_dev.c
index 9e56ee1f2652..1cbbc794edc6 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -417,7 +417,7 @@  __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter, int nr_pages)
 		dio->size += bio->bi_iter.bi_size;
 		pos += bio->bi_iter.bi_size;
 
-		nr_pages = iov_iter_npages(iter, BIO_MAX_PAGES);
+		nr_pages = bio_iov_vecs_to_alloc(iter, BIO_MAX_PAGES);
 		if (!nr_pages) {
 			bool polled = false;
 
@@ -482,9 +482,10 @@  blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter)
 {
 	int nr_pages;
 
-	nr_pages = iov_iter_npages(iter, BIO_MAX_PAGES + 1);
-	if (!nr_pages)
+	if (!iov_iter_count(iter))
 		return 0;
+
+	nr_pages = bio_iov_vecs_to_alloc(iter, BIO_MAX_PAGES + 1);
 	if (is_sync_kiocb(iocb) && nr_pages <= BIO_MAX_PAGES)
 		return __blkdev_direct_IO_simple(iocb, iter, nr_pages);
 
diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
index 933f234d5bec..ea1e8f696076 100644
--- a/fs/iomap/direct-io.c
+++ b/fs/iomap/direct-io.c
@@ -250,11 +250,8 @@  iomap_dio_bio_actor(struct inode *inode, loff_t pos, loff_t length,
 	orig_count = iov_iter_count(dio->submit.iter);
 	iov_iter_truncate(dio->submit.iter, length);
 
-	nr_pages = iov_iter_npages(dio->submit.iter, BIO_MAX_PAGES);
-	if (nr_pages <= 0) {
-		ret = nr_pages;
+	if (!iov_iter_count(dio->submit.iter))
 		goto out;
-	}
 
 	if (need_zeroout) {
 		/* zero out from the start of the block to the write offset */
@@ -263,6 +260,7 @@  iomap_dio_bio_actor(struct inode *inode, loff_t pos, loff_t length,
 			iomap_dio_zero(dio, iomap, pos - pad, pad);
 	}
 
+	nr_pages = bio_iov_vecs_to_alloc(dio->submit.iter, BIO_MAX_PAGES);
 	do {
 		size_t n;
 		if (dio->error) {
@@ -308,7 +306,8 @@  iomap_dio_bio_actor(struct inode *inode, loff_t pos, loff_t length,
 		dio->size += n;
 		copied += n;
 
-		nr_pages = iov_iter_npages(dio->submit.iter, BIO_MAX_PAGES);
+		nr_pages = bio_iov_vecs_to_alloc(dio->submit.iter,
+						 BIO_MAX_PAGES);
 		iomap_dio_submit_bio(dio, iomap, bio, pos);
 		pos += n;
 	} while (nr_pages);
diff --git a/include/linux/bio.h b/include/linux/bio.h
index 1edda614f7ce..2a9f3f0bbe0a 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -10,6 +10,7 @@ 
 #include <linux/ioprio.h>
 /* struct bio, bio_vec and BIO_* flags are defined in blk_types.h */
 #include <linux/blk_types.h>
+#include <linux/uio.h>
 
 #define BIO_DEBUG
 
@@ -441,6 +442,11 @@  static inline void bio_wouldblock_error(struct bio *bio)
 	bio_endio(bio);
 }
 
+static inline int bio_iov_vecs_to_alloc(struct iov_iter *iter, int max_segs)
+{
+	return iov_iter_npages(iter, max_segs);
+}
+
 struct request_queue;
 
 extern int submit_bio_wait(struct bio *bio);