Re: [PATCH v2 4/9] exfat: add support for multi-cluster allocation
From: Chi Zhiling
Date: Sun May 10 2026 - 09:33:50 EST
On 5/7/26 8:42 PM, Namjae Jeon wrote:
Currently exfat_map_cluster() allocates and returns only one cluster
at a time even when more clusters are needed. This causes multiple
FAT walks and repeated allocation calls during large sequential writes
or when using iomap for writes. This change exfat_map_cluster() and
exfat_alloc_cluster() to be able to allocate multiple contiguous
clusters.
Signed-off-by: Namjae Jeon <linkinjeon@xxxxxxxxxx>
---
fs/exfat/dir.c | 2 +-
fs/exfat/exfat_fs.h | 2 +-
fs/exfat/fatent.c | 26 ++++++++++++++++----------
fs/exfat/file.c | 2 +-
fs/exfat/inode.c | 23 ++++++-----------------
fs/exfat/namei.c | 2 +-
6 files changed, 26 insertions(+), 31 deletions(-)
diff --git a/fs/exfat/dir.c b/fs/exfat/dir.c
index ca9d707220df..37f324399b6b 100644
--- a/fs/exfat/dir.c
+++ b/fs/exfat/dir.c
@@ -295,7 +295,7 @@ int exfat_alloc_new_dir(struct inode *inode, struct exfat_chain *clu)
exfat_chain_set(clu, EXFAT_EOF_CLUSTER, 0, ALLOC_NO_FAT_CHAIN);
- ret = exfat_alloc_cluster(inode, 1, clu, IS_DIRSYNC(inode));
+ ret = exfat_alloc_cluster(inode, 1, clu, IS_DIRSYNC(inode), false);
if (ret)
return ret;
diff --git a/fs/exfat/exfat_fs.h b/fs/exfat/exfat_fs.h
index 9c8ab3df7a42..6e7fd6822b01 100644
--- a/fs/exfat/exfat_fs.h
+++ b/fs/exfat/exfat_fs.h
@@ -497,7 +497,7 @@ int exfat_clear_volume_dirty(struct super_block *sb);
exfat_cluster_walk(sb, (pclu), 1, ALLOC_FAT_CHAIN)
int exfat_alloc_cluster(struct inode *inode, unsigned int num_alloc,
- struct exfat_chain *p_chain, bool sync_bmap);
+ struct exfat_chain *p_chain, bool sync_bmap, bool contig);
int exfat_free_cluster(struct inode *inode, struct exfat_chain *p_chain);
int exfat_ent_get(struct super_block *sb, unsigned int loc,
unsigned int *content, struct buffer_head **last);
diff --git a/fs/exfat/fatent.c b/fs/exfat/fatent.c
index 45b0b754a2e4..a917c954bd23 100644
--- a/fs/exfat/fatent.c
+++ b/fs/exfat/fatent.c
@@ -419,7 +419,7 @@ int exfat_zeroed_cluster(struct inode *dir, unsigned int clu)
}
int exfat_alloc_cluster(struct inode *inode, unsigned int num_alloc,
- struct exfat_chain *p_chain, bool sync_bmap)
+ struct exfat_chain *p_chain, bool sync_bmap, bool contig)
{
int ret = -ENOSPC;
unsigned int total_cnt;
@@ -470,14 +470,20 @@ int exfat_alloc_cluster(struct inode *inode, unsigned int num_alloc,
while ((new_clu = exfat_find_free_bitmap(sb, hint_clu)) !=
EXFAT_EOF_CLUSTER) {
- if (new_clu != hint_clu &&
- p_chain->flags == ALLOC_NO_FAT_CHAIN) {
- if (exfat_chain_cont_cluster(sb, p_chain->dir,
- p_chain->size)) {
- ret = -EIO;
- goto free_cluster;
+ if (new_clu != hint_clu) {
+ if (p_chain->flags == ALLOC_NO_FAT_CHAIN) {
+ if (exfat_chain_cont_cluster(sb, p_chain->dir,
+ p_chain->size)) {
+ ret = -EIO;
+ goto free_cluster;
+ }
+ p_chain->flags = ALLOC_FAT_CHAIN;
+ }
+
+ if (contig && p_chain->size > 0) {
+ hint_clu--;
+ goto done;
}
- p_chain->flags = ALLOC_FAT_CHAIN;
}
/* update allocation bitmap */
@@ -507,9 +513,9 @@ int exfat_alloc_cluster(struct inode *inode, unsigned int num_alloc,
last_clu = new_clu;
if (p_chain->size == num_alloc) {
+done:
sbi->clu_srch_ptr = hint_clu;
- sbi->used_clusters += num_alloc;
-
+ sbi->used_clusters += p_chain->size;
mutex_unlock(&sbi->bitmap_lock);
return 0;
}
diff --git a/fs/exfat/file.c b/fs/exfat/file.c
index b7a4964631a0..15b9d6a1766a 100644
--- a/fs/exfat/file.c
+++ b/fs/exfat/file.c
@@ -56,7 +56,7 @@ static int exfat_cont_expand(struct inode *inode, loff_t size)
clu.flags = ei->flags;
ret = exfat_alloc_cluster(inode, new_num_clusters - num_clusters,
- &clu, inode_needs_sync(inode));
+ &clu, inode_needs_sync(inode), false);
if (ret)
return ret;
diff --git a/fs/exfat/inode.c b/fs/exfat/inode.c
index 1246713567a5..7b09d94ac464 100644
--- a/fs/exfat/inode.c
+++ b/fs/exfat/inode.c
@@ -137,9 +137,9 @@ static int exfat_map_cluster(struct inode *inode, unsigned int clu_offset,
unsigned int num_to_be_allocated = 0, num_clusters;
num_clusters = exfat_bytes_to_cluster(sbi, exfat_ondisk_size(inode));
-
- if (clu_offset >= num_clusters)
- num_to_be_allocated = clu_offset - num_clusters + 1;
+ if (clu_offset > num_clusters ||
+ *count > num_clusters - clu_offset)
+ num_to_be_allocated = clu_offset + *count - num_clusters;
We need to truncate *count for read operations so that it does not extend beyond EOF. Otherwise, xfstests generic/003 will fail.
thanks,
if (!create && (num_to_be_allocated > 0)) {
*clu = EXFAT_EOF_CLUSTER;
@@ -182,7 +182,7 @@ static int exfat_map_cluster(struct inode *inode, unsigned int clu_offset,
}
ret = exfat_alloc_cluster(inode, num_to_be_allocated, &new_clu,
- inode_needs_sync(inode));
+ inode_needs_sync(inode), true);
if (ret)
return ret;
@@ -216,20 +216,9 @@ static int exfat_map_cluster(struct inode *inode, unsigned int clu_offset,
}
*clu = new_clu.dir;
+ *count = new_clu.size;
- inode->i_blocks +=
- exfat_cluster_to_sectors(sbi, num_to_be_allocated) >> 9;
-
- /*
- * Move *clu pointer along FAT chains (hole care) because the
- * caller of this function expect *clu to be the last cluster.
- * This only works when num_to_be_allocated >= 2,
- * *clu = (the first cluster of the allocated chain) =>
- * (the last cluster of ...)
- */
- if (exfat_cluster_walk(sb, clu, num_to_be_allocated - 1, ei->flags))
- return -EIO;
- *count = 1;
+ inode->i_blocks += exfat_cluster_to_sectors(sbi, new_clu.size);
if (balloc)
*balloc = true;
}
diff --git a/fs/exfat/namei.c b/fs/exfat/namei.c
index 752fbec9316b..87e55c5c1bf4 100644
--- a/fs/exfat/namei.c
+++ b/fs/exfat/namei.c
@@ -341,7 +341,7 @@ int exfat_find_empty_entry(struct inode *inode,
}
/* allocate a cluster */
- ret = exfat_alloc_cluster(inode, 1, &clu, IS_DIRSYNC(inode));
+ ret = exfat_alloc_cluster(inode, 1, &clu, IS_DIRSYNC(inode), false);
if (ret)
return ret;