linux-ext4 - [PATCH 1/3] fuse2fs: enable caching of iomaps

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Message-ID: <175798162669.391696.2292027654285998318.stgit@frogsfrogsfrogs>
Date: Mon, 15 Sep 2025 18:06:18 -0700
From: "Darrick J. Wong" <djwong@...nel.org>
To: tytso@....edu
Cc: miklos@...redi.hu, neal@...pa.dev, linux-fsdevel@...r.kernel.org,
 linux-ext4@...r.kernel.org, John@...ves.net, bernd@...ernd.com,
 joannelkoong@...il.com
Subject: [PATCH 1/3] fuse2fs: enable caching of iomaps

From: Darrick J. Wong <djwong@...nel.org>

Cache the iomaps we generate in the kernel for better performance.

Signed-off-by: "Darrick J. Wong" <djwong@...nel.org>
---
 fuse4fs/fuse4fs.c |   25 +++++++++++++++++++++++++
 misc/fuse2fs.c    |   24 ++++++++++++++++++++++++
 2 files changed, 49 insertions(+)


diff --git a/fuse4fs/fuse4fs.c b/fuse4fs/fuse4fs.c
index a7709a7e6fb699..6ab660b36d0472 100644
--- a/fuse4fs/fuse4fs.c
+++ b/fuse4fs/fuse4fs.c
@@ -284,6 +284,8 @@ struct fuse4fs {
 #ifdef STATX_WRITE_ATOMIC
 	unsigned int awu_min, awu_max;
 #endif
+	/* options set by fuse_opt_parse must be of type int */
+	int iomap_cache;
 #endif
 	unsigned int blockmask;
 	unsigned long offset;
@@ -6373,6 +6375,24 @@ static void op_iomap_begin(fuse_req_t req, fuse_ino_t fino, uint64_t dontcare,
 	if (opflags & FUSE_IOMAP_OP_ATOMIC)
 		read.flags |= FUSE_IOMAP_F_ATOMIC_BIO;
 
+	/*
+	 * Cache the mapping in the kernel so that we can reuse them for
+	 * subsequent IO.
+	 */
+	if (ff->iomap_cache) {
+		ret = fuse_lowlevel_notify_iomap_upsert(ff->fuse, fino, ino,
+							&read, NULL);
+		if (ret) {
+			ret = translate_error(fs, ino, -ret);
+			goto out_unlock;
+		} else {
+			/* Tell the kernel to retry from cache */
+			read.type = FUSE_IOMAP_TYPE_RETRY_CACHE;
+			read.dev = FUSE_IOMAP_DEV_NULL;
+			read.addr = FUSE_IOMAP_NULL_ADDR;
+		}
+	}
+
 out_unlock:
 	fuse4fs_finish(ff, ret);
 	if (ret)
@@ -7183,6 +7203,10 @@ static struct fuse_opt fuse4fs_opts[] = {
 	FUSE4FS_OPT("timing",		timing,			1),
 #endif
 	FUSE4FS_OPT("noblkdev",		noblkdev,		1),
+#ifdef HAVE_FUSE_IOMAP
+	FUSE4FS_OPT("iomap_cache",	iomap_cache,		1),
+	FUSE4FS_OPT("noiomap_cache",	iomap_cache,		0),
+#endif
 
 #ifdef HAVE_FUSE_IOMAP
 #ifdef MS_LAZYTIME
@@ -7517,6 +7541,7 @@ int main(int argc, char *argv[])
 		.iomap_want = FT_DEFAULT,
 		.iomap_state = IOMAP_UNKNOWN,
 		.iomap_dev = FUSE_IOMAP_DEV_NULL,
+		.iomap_cache = 1,
 #endif
 		.translate_inums = 1,
 		.write_gdt_on_destroy = 1,
diff --git a/misc/fuse2fs.c b/misc/fuse2fs.c
index 260d1b77e3f24b..14a1ceeea46a0b 100644
--- a/misc/fuse2fs.c
+++ b/misc/fuse2fs.c
@@ -277,6 +277,8 @@ struct fuse2fs {
 #ifdef STATX_WRITE_ATOMIC
 	unsigned int awu_min, awu_max;
 #endif
+	/* options set by fuse_opt_parse must be of type int */
+	int iomap_cache;
 #endif
 	unsigned int blockmask;
 	unsigned long offset;
@@ -5942,6 +5944,23 @@ static int op_iomap_begin(const char *path, uint64_t nodeid, uint64_t attr_ino,
 	if (opflags & FUSE_IOMAP_OP_ATOMIC)
 		read->flags |= FUSE_IOMAP_F_ATOMIC_BIO;
 
+	/*
+	 * Cache the mapping in the kernel so that we can reuse them for
+	 * subsequent IO.
+	 */
+	if (ff->iomap_cache) {
+		ret = fuse_fs_iomap_upsert(nodeid, attr_ino, read, NULL);
+		if (ret) {
+			ret = translate_error(fs, attr_ino, -ret);
+			goto out_unlock;
+		} else {
+			/* Tell the kernel to retry from cache */
+			read->type = FUSE_IOMAP_TYPE_RETRY_CACHE;
+			read->dev = FUSE_IOMAP_DEV_NULL;
+			read->addr = FUSE_IOMAP_NULL_ADDR;
+		}
+	}
+
 out_unlock:
 	fuse2fs_finish(ff, ret);
 	return ret;
@@ -6744,6 +6763,10 @@ static struct fuse_opt fuse2fs_opts[] = {
 	FUSE2FS_OPT("timing",		timing,			1),
 #endif
 	FUSE2FS_OPT("noblkdev",		noblkdev,		1),
+#ifdef HAVE_FUSE_IOMAP
+	FUSE2FS_OPT("iomap_cache",	iomap_cache,		1),
+	FUSE2FS_OPT("noiomap_cache",	iomap_cache,		0),
+#endif
 
 #ifdef HAVE_FUSE_IOMAP
 #ifdef MS_LAZYTIME
@@ -6978,6 +7001,7 @@ int main(int argc, char *argv[])
 		.iomap_want = FT_DEFAULT,
 		.iomap_state = IOMAP_UNKNOWN,
 		.iomap_dev = FUSE_IOMAP_DEV_NULL,
+		.iomap_cache = 1,
 #endif
 		.write_gdt_on_destroy = 1,
 	};