On 8/5/25 07:05, Daniel Lee wrote: > For casefolded directories, f2fs may fall back to a linear search if > a hash-based lookup fails. This can cause severe performance > regressions. > > While this behavior can be controlled by userspace tools (e.g. mkfs, > fsck) by setting an on-disk flag, a kernel-level solution is needed > to guarantee the lookup behavior regardless of the on-disk state. > > This commit introduces the 'lookup_mode' mount option to provide this > kernel-side control. > > The option accepts three values: > - perf: (Default) Enforces a hash-only lookup. The linear fallback > is always disabled. > - compat: Enables the linear search fallback for compatibility with > directory entries from older kernels. > - auto: Determines the mode based on the on-disk flag, preserving the > userspace-based behavior. > > Signed-off-by: Daniel Lee <[email protected]> > --- > v2: > - rework mount option parsing to use the new mount API. > - add lookup_mode field to struct f2fs_mount_info. > - add show_options support for the new option. > Documentation/filesystems/f2fs.rst | 19 +++++++++++++++++++ > fs/f2fs/dir.c | 17 ++++++++++++++++- > fs/f2fs/f2fs.h | 7 +++++++ > fs/f2fs/super.c | 25 +++++++++++++++++++++++++ > 4 files changed, 67 insertions(+), 1 deletion(-) > > diff --git a/Documentation/filesystems/f2fs.rst > b/Documentation/filesystems/f2fs.rst > index 03b1efa6d3b2..a80ed82a547a 100644 > --- a/Documentation/filesystems/f2fs.rst > +++ b/Documentation/filesystems/f2fs.rst > @@ -370,6 +370,25 @@ errors=%s Specify f2fs behavior on > critical errors. This supports modes: > ====================== =============== =============== > ======== > nat_bits Enable nat_bits feature to enhance full/empty nat > blocks access, > by default it's disabled. > +lookup_mode=%s Control the directory lookup behavior for > casefolded > + directories. This option has no effect on directories > + that do not have the casefold feature enabled. > + > + ================== > ======================================== > + Value Description > + ================== > ======================================== > + perf (Default) Enforces a hash-only > lookup. > + The linear search fallback is always > + disabled, ignoring the on-disk flag. > + compat Enables the linear search fallback > for > + compatibility with directory entries > + created by older kernel that used a > + different case-folding algorithm. > + This mode ignores the on-disk flag. > + auto F2FS determines the mode based on > the > + on-disk > `SB_ENC_NO_COMPAT_FALLBACK_FL` > + flag. > + ================== > ======================================== > ======================== > ============================================================ > > Debugfs Entries > diff --git a/fs/f2fs/dir.c b/fs/f2fs/dir.c > index fffd7749d6d1..48f4f98afb01 100644 > --- a/fs/f2fs/dir.c > +++ b/fs/f2fs/dir.c > @@ -16,6 +16,21 @@ > #include "xattr.h" > #include <trace/events/f2fs.h> > > +static inline bool f2fs_should_fallback_to_linear(struct inode *dir) > +{ > + struct f2fs_sb_info *sbi = F2FS_I_SB(dir); > + > + switch (F2FS_OPTION(sbi).lookup_mode) { > + case LOOKUP_PERF: > + return false; > + case LOOKUP_COMPAT: > + return true; > + case LOOKUP_AUTO: > + return !sb_no_casefold_compat_fallback(sbi->sb); > + } > + return false; > +} > + > #if IS_ENABLED(CONFIG_UNICODE) > extern struct kmem_cache *f2fs_cf_name_slab; > #endif > @@ -366,7 +381,7 @@ struct f2fs_dir_entry *__f2fs_find_entry(struct inode > *dir, > > out: > #if IS_ENABLED(CONFIG_UNICODE) > - if (!sb_no_casefold_compat_fallback(dir->i_sb) && > + if (f2fs_should_fallback_to_linear(dir) && > IS_CASEFOLDED(dir) && !de && use_hash) { > use_hash = false; > goto start_find_entry; > diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h > index 7029aa8b430e..1c0edb8a7134 100644 > --- a/fs/f2fs/f2fs.h > +++ b/fs/f2fs/f2fs.h > @@ -212,6 +212,7 @@ struct f2fs_mount_info { > int compress_mode; /* compression mode */ > unsigned char extensions[COMPRESS_EXT_NUM][F2FS_EXTENSION_LEN]; /* > extensions */ > unsigned char noextensions[COMPRESS_EXT_NUM][F2FS_EXTENSION_LEN]; /* > extensions */ > + unsigned int lookup_mode; > }; > > #define F2FS_FEATURE_ENCRYPT 0x00000001 > @@ -1448,6 +1449,12 @@ enum { > TOTAL_CALL = FOREGROUND, > }; > > +enum f2fs_lookup_mode { > + LOOKUP_PERF, > + LOOKUP_COMPAT, > + LOOKUP_AUTO, > +}; > + > static inline int f2fs_test_bit(unsigned int nr, char *addr); > static inline void f2fs_set_bit(unsigned int nr, char *addr); > static inline void f2fs_clear_bit(unsigned int nr, char *addr); > diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c > index e16c4e2830c2..ed17ab4d5cef 100644 > --- a/fs/f2fs/super.c > +++ b/fs/f2fs/super.c > @@ -181,6 +181,7 @@ enum { > Opt_nat_bits, > Opt_jqfmt, > Opt_checkpoint, > + Opt_lookup_mode, > Opt_err, > }; > > @@ -244,6 +245,13 @@ static const struct constant_table f2fs_param_errors[] = > { > {} > }; > > +static const struct constant_table f2fs_param_lookup_mode[] = { > + {"perf", LOOKUP_PERF}, > + {"compat", LOOKUP_COMPAT}, > + {"auto", LOOKUP_AUTO}, > + {} > +}; > + > static const struct fs_parameter_spec f2fs_param_specs[] = { > fsparam_enum("background_gc", Opt_gc_background, > f2fs_param_background_gc), > fsparam_flag("disable_roll_forward", Opt_disable_roll_forward), > @@ -300,6 +308,7 @@ static const struct fs_parameter_spec f2fs_param_specs[] > = { > fsparam_enum("memory", Opt_memory_mode, f2fs_param_memory_mode), > fsparam_flag("age_extent_cache", Opt_age_extent_cache), > fsparam_enum("errors", Opt_errors, f2fs_param_errors), > + fsparam_enum("lookup_mode", Opt_lookup_mode, f2fs_param_lookup_mode), > {} > }; > > @@ -336,6 +345,7 @@ static match_table_t f2fs_checkpoint_tokens = { > #define F2FS_SPEC_discard_unit (1 << 21) > #define F2FS_SPEC_memory_mode (1 << 22) > #define F2FS_SPEC_errors (1 << 23) > +#define F2FS_SPEC_lookup_mode (1 << 24) > > struct f2fs_fs_context { > struct f2fs_mount_info info; > @@ -1143,6 +1153,10 @@ static int f2fs_parse_param(struct fs_context *fc, > struct fs_parameter *param) > case Opt_nat_bits: > ctx_set_opt(ctx, F2FS_MOUNT_NAT_BITS); > break; > + case Opt_lookup_mode: > + F2FS_CTX_INFO(ctx).lookup_mode = result.uint_32; > + ctx->spec_mask |= F2FS_SPEC_lookup_mode; > + break; > } > return 0; > } > @@ -1652,6 +1666,8 @@ static void f2fs_apply_options(struct fs_context *fc, > struct super_block *sb) > F2FS_OPTION(sbi).memory_mode = F2FS_CTX_INFO(ctx).memory_mode; > if (ctx->spec_mask & F2FS_SPEC_errors) > F2FS_OPTION(sbi).errors = F2FS_CTX_INFO(ctx).errors; > + if (ctx->spec_mask & F2FS_SPEC_lookup_mode) > + F2FS_OPTION(sbi).lookup_mode = F2FS_CTX_INFO(ctx).lookup_mode; > > f2fs_apply_compression(fc, sb); > f2fs_apply_test_dummy_encryption(fc, sb); > @@ -2416,6 +2432,13 @@ static int f2fs_show_options(struct seq_file *seq, > struct dentry *root) > if (test_opt(sbi, NAT_BITS)) > seq_puts(seq, ",nat_bits"); > > + if (F2FS_OPTION(sbi).lookup_mode != LOOKUP_PERF) { > + if (F2FS_OPTION(sbi).lookup_mode == LOOKUP_COMPAT) > + seq_show_option(seq, "lookup_mode", "compat"); > + else if (F2FS_OPTION(sbi).lookup_mode == LOOKUP_AUTO) > + seq_show_option(seq, "lookup_mode", "auto");
Can we show "lookup_mode=perf" in mount option as well? Thanks, > + } > + > return 0; > } > > @@ -2480,6 +2503,8 @@ static void default_options(struct f2fs_sb_info *sbi, > bool remount) > #endif > > f2fs_build_fault_attr(sbi, 0, 0, FAULT_ALL); > + > + F2FS_OPTION(sbi).lookup_mode = LOOKUP_PERF; > } > > #ifdef CONFIG_QUOTA _______________________________________________ Linux-f2fs-devel mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
