This patch supports to readahead more blocks in erofs_readdir(), it can
enhance readdir performance in large direcotry.
readdir test in a large directory which contains 12000 sub-files.
files_per_second
Before: 926385.54
After: 2380435.562
Meanwhile, let's introduces a new sysfs entry to control readahead
bytes to provide more flexible policy for readahead of readdir().
- location: /sys/fs/erofs/<disk>/dir_ra_bytes
- default value: 16384
- disable readahead: set the value to 0
Signed-off-by: Chao Yu <c...@kernel.org>
---
v4:
- clean up codes and comments
Documentation/ABI/testing/sysfs-fs-erofs | 8 ++++++++
fs/erofs/dir.c | 14 ++++++++++++++
fs/erofs/internal.h | 4 ++++
fs/erofs/super.c | 2 ++
fs/erofs/sysfs.c | 2 ++
5 files changed, 30 insertions(+)
diff --git a/Documentation/ABI/testing/sysfs-fs-erofs
b/Documentation/ABI/testing/sysfs-fs-erofs
index bf3b6299c15e..85fa56ca092c 100644
--- a/Documentation/ABI/testing/sysfs-fs-erofs
+++ b/Documentation/ABI/testing/sysfs-fs-erofs
@@ -35,3 +35,11 @@ Description: Used to set or show hardware accelerators in
effect
and multiple accelerators are separated by '\n'.
Supported accelerator(s): qat_deflate.
Disable all accelerators with an empty string (echo > accel).
+
+What: /sys/fs/erofs/<disk>/dir_ra_bytes
+Date: July 2025
+Contact: "Chao Yu" <c...@kernel.org>
+Description: Used to set or show readahead bytes during readdir(), by
+ default the value is 16384.
+
+ - 0: disable readahead.
diff --git a/fs/erofs/dir.c b/fs/erofs/dir.c
index 3e4b38bec0aa..99745c272b60 100644
--- a/fs/erofs/dir.c
+++ b/fs/erofs/dir.c
@@ -47,8 +47,12 @@ static int erofs_readdir(struct file *f, struct dir_context
*ctx)
struct inode *dir = file_inode(f);
struct erofs_buf buf = __EROFS_BUF_INITIALIZER;
struct super_block *sb = dir->i_sb;
+ struct file_ra_state *ra = &f->f_ra;
unsigned long bsz = sb->s_blocksize;
unsigned int ofs = erofs_blkoff(sb, ctx->pos);
+ pgoff_t ra_pages = DIV_ROUND_UP_POW2(
+ EROFS_I_SB(dir)->dir_ra_bytes, PAGE_SIZE);
+ pgoff_t nr_pages = DIV_ROUND_UP_POW2(dir->i_size, PAGE_SIZE);
int err = 0;
bool initial = true;
@@ -63,6 +67,16 @@ static int erofs_readdir(struct file *f, struct dir_context
*ctx)
break;
}
+ /* readahead blocks to enhance performance in large directory */
+ if (ra_pages) {
+ pgoff_t idx = DIV_ROUND_UP(ctx->pos, PAGE_SIZE);
+ pgoff_t pages = min(nr_pages - idx, ra_pages);
+
+ if (pages > 1 && !ra_has_index(ra, idx))
+ page_cache_sync_readahead(dir->i_mapping, ra,
+ f, idx, pages);
+ }
+
de = erofs_bread(&buf, dbstart, true);
if (IS_ERR(de)) {
erofs_err(sb, "failed to readdir of logical block %llu
of nid %llu",
diff --git a/fs/erofs/internal.h b/fs/erofs/internal.h
index 0d19bde8c094..8b1372521790 100644
--- a/fs/erofs/internal.h
+++ b/fs/erofs/internal.h
@@ -157,6 +157,7 @@ struct erofs_sb_info {
/* sysfs support */
struct kobject s_kobj; /* /sys/fs/erofs/<devname> */
struct completion s_kobj_unregister;
+ erofs_off_t dir_ra_bytes;
/* fscache support */
struct fscache_volume *volume;
@@ -238,6 +239,9 @@ EROFS_FEATURE_FUNCS(xattr_filter, compat,
COMPAT_XATTR_FILTER)
#define EROFS_I_BL_XATTR_BIT (BITS_PER_LONG - 1)
#define EROFS_I_BL_Z_BIT (BITS_PER_LONG - 2)
+/* default readahead size of directories */
+#define EROFS_DIR_RA_BYTES 16384
+
struct erofs_inode {
erofs_nid_t nid;
diff --git a/fs/erofs/super.c b/fs/erofs/super.c
index e1e9f06e8342..38fc4813a896 100644
--- a/fs/erofs/super.c
+++ b/fs/erofs/super.c
@@ -715,6 +715,8 @@ static int erofs_fc_fill_super(struct super_block *sb,
struct fs_context *fc)
if (err)
return err;
+ sbi->dir_ra_bytes = EROFS_DIR_RA_BYTES;
+
erofs_info(sb, "mounted with root inode @ nid %llu.", sbi->root_nid);
return 0;
}
diff --git a/fs/erofs/sysfs.c b/fs/erofs/sysfs.c
index eed8797a193f..9d9f820a5621 100644
--- a/fs/erofs/sysfs.c
+++ b/fs/erofs/sysfs.c
@@ -65,12 +65,14 @@ EROFS_ATTR_FUNC(drop_caches, 0200);
#ifdef CONFIG_EROFS_FS_ZIP_ACCEL
EROFS_ATTR_FUNC(accel, 0644);
#endif
+EROFS_ATTR_RW_UI(dir_ra_bytes, erofs_sb_info);
static struct attribute *erofs_sb_attrs[] = {
#ifdef CONFIG_EROFS_FS_ZIP
ATTR_LIST(sync_decompress),
ATTR_LIST(drop_caches),
#endif
+ ATTR_LIST(dir_ra_bytes),
NULL,
};
ATTRIBUTE_GROUPS(erofs_sb);
--
2.49.0
