linux-kernel - [PATCH] iomap: use largest_zero_folio() in iomap_dio

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Message-ID: <20250814142137.45469-1-kernel@pankajraghav.com>
Date: Thu, 14 Aug 2025 16:21:37 +0200
From: "Pankaj Raghav (Samsung)" <kernel@...kajraghav.com>
To: "Darrick J . Wong" <djwong@...nel.org>,
	Christian Brauner <brauner@...nel.org>
Cc: linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org,
	mcgrof@...nel.org,
	gost.dev@...sung.com,
	linux-xfs@...r.kernel.org,
	kernel@...kajraghav.com,
	Pankaj Raghav <p.raghav@...sung.com>
Subject: [PATCH] iomap: use largest_zero_folio() in iomap_dio_zero()

From: Pankaj Raghav <p.raghav@...sung.com>

iomap_dio_zero() uses a custom allocated memory of zeroes for padding
zeroes. This was a temporary solution until there was a way to request a
zero folio that was greater than the PAGE_SIZE.

Use largest_zero_folio() function instead of using the custom allocated
memory of zeroes. There is no guarantee from largest_zero_folio()
function that it will always return a PMD sized folio. Adapt the code so
that it can also work if largest_zero_folio() returns a ZERO_PAGE.

Signed-off-by: Pankaj Raghav <p.raghav@...sung.com>
---
 fs/iomap/direct-io.c | 38 +++++++++++++++-----------------------
 1 file changed, 15 insertions(+), 23 deletions(-)

diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
index b84f6af2eb4c..a7a281ea3e50 100644
--- a/fs/iomap/direct-io.c
+++ b/fs/iomap/direct-io.c
@@ -24,13 +24,6 @@
 #define IOMAP_DIO_WRITE		(1U << 30)
 #define IOMAP_DIO_DIRTY		(1U << 31)
 
-/*
- * Used for sub block zeroing in iomap_dio_zero()
- */
-#define IOMAP_ZERO_PAGE_SIZE (SZ_64K)
-#define IOMAP_ZERO_PAGE_ORDER (get_order(IOMAP_ZERO_PAGE_SIZE))
-static struct page *zero_page;
-
 struct iomap_dio {
 	struct kiocb		*iocb;
 	const struct iomap_dio_ops *dops;
@@ -285,24 +278,35 @@ static int iomap_dio_zero(const struct iomap_iter *iter, struct iomap_dio *dio,
 {
 	struct inode *inode = file_inode(dio->iocb->ki_filp);
 	struct bio *bio;
+	struct folio *zero_folio = largest_zero_folio();
+	int nr_vecs = max(1, i_blocksize(inode) / folio_size(zero_folio));
 
 	if (!len)
 		return 0;
+
 	/*
-	 * Max block size supported is 64k
+	 * This limit shall never be reached as most filesystems have a
+	 * maximum blocksize of 64k.
 	 */
-	if (WARN_ON_ONCE(len > IOMAP_ZERO_PAGE_SIZE))
+	if (WARN_ON_ONCE(nr_vecs > BIO_MAX_VECS))
 		return -EINVAL;
 
-	bio = iomap_dio_alloc_bio(iter, dio, 1, REQ_OP_WRITE | REQ_SYNC | REQ_IDLE);
+	bio = iomap_dio_alloc_bio(iter, dio, nr_vecs,
+				  REQ_OP_WRITE | REQ_SYNC | REQ_IDLE);
 	fscrypt_set_bio_crypt_ctx(bio, inode, pos >> inode->i_blkbits,
 				  GFP_KERNEL);
 	bio->bi_iter.bi_sector = iomap_sector(&iter->iomap, pos);
 	bio->bi_private = dio;
 	bio->bi_end_io = iomap_dio_bio_end_io;
 
-	__bio_add_page(bio, zero_page, len, 0);
+	while (len > 0) {
+		unsigned int io_len = min(len, folio_size(zero_folio));
+
+		bio_add_folio_nofail(bio, zero_folio, io_len, 0);
+		len -= io_len;
+	}
 	iomap_dio_submit_bio(iter, dio, bio, pos);
+
 	return 0;
 }
 
@@ -822,15 +826,3 @@ iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
 	return iomap_dio_complete(dio);
 }
 EXPORT_SYMBOL_GPL(iomap_dio_rw);
-
-static int __init iomap_dio_init(void)
-{
-	zero_page = alloc_pages(GFP_KERNEL | __GFP_ZERO,
-				IOMAP_ZERO_PAGE_ORDER);
-
-	if (!zero_page)
-		return -ENOMEM;
-
-	return 0;
-}
-fs_initcall(iomap_dio_init);

base-commit: 931e46dcbc7e6035a90e9c4a27a84b660e083f0a
-- 
2.50.1