linux-kernel - [RFC 3/3] iomap: use LARGE_ZERO_PAGE in iomap_dio

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Message-ID: <20250516101054.676046-4-p.raghav@samsung.com>
Date: Fri, 16 May 2025 12:10:54 +0200
From: Pankaj Raghav <p.raghav@...sung.com>
To: "Darrick J . Wong" <djwong@...nel.org>,
	hch@....de,
	willy@...radead.org
Cc: linux-kernel@...r.kernel.org,
	linux-mm@...ck.org,
	David Hildenbrand <david@...hat.com>,
	linux-fsdevel@...r.kernel.org,
	mcgrof@...nel.org,
	gost.dev@...sung.com,
	Andrew Morton <akpm@...ux-foundation.org>,
	kernel@...kajraghav.com,
	Pankaj Raghav <p.raghav@...sung.com>
Subject: [RFC 3/3] iomap: use LARGE_ZERO_PAGE in iomap_dio_zero()

Use LARGE_ZERO_PAGE instead of custom allocated 64k zero pages. The
downside is we might end up using ZERO_PAGE on systems that do not
enable LARGE_ZERO_PAGE feature.

Signed-off-by: Pankaj Raghav <p.raghav@...sung.com>
---
 fs/iomap/direct-io.c | 31 +++++++++----------------------
 1 file changed, 9 insertions(+), 22 deletions(-)

diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
index 844261a31156..6a2b6726a156 100644
--- a/fs/iomap/direct-io.c
+++ b/fs/iomap/direct-io.c
@@ -29,13 +29,6 @@
 #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;
@@ -290,23 +283,29 @@ 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;
+	int nr_vecs = max(1, i_blocksize(inode) / ZERO_LARGE_PAGE_SIZE);
 
 	if (!len)
 		return 0;
 	/*
 	 * Max block size supported is 64k
 	 */
-	if (WARN_ON_ONCE(len > IOMAP_ZERO_PAGE_SIZE))
+	if (WARN_ON_ONCE(len > SZ_64K))
 		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) {
+		unsigned int io_len = min_t(unsigned int, len, ZERO_LARGE_PAGE_SIZE);
+
+		__bio_add_page(bio, ZERO_LARGE_PAGE(0), len, 0);
+		len -= io_len;
+	}
 	iomap_dio_submit_bio(iter, dio, bio, pos);
 	return 0;
 }
@@ -827,15 +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);
-- 
2.47.2