Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel
os
linux
f2fs: add lookup_mode mount option
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 <chullee@google.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
authored by
Daniel Lee
and committed by
Jaegeuk Kim
632f0b6c
76bb6a72
+67
-1
+19
Documentation/filesystems/f2fs.rst
+19
Documentation/filesystems/f2fs.rst
···
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====================== =============== =============== ========
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nat_bits Enable nat_bits feature to enhance full/empty nat blocks access,
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by default it's disabled.
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+
lookup_mode=%s Control the directory lookup behavior for casefolded
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directories. This option has no effect on directories
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that do not have the casefold feature enabled.
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+
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================== ========================================
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Value Description
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================== ========================================
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perf (Default) Enforces a hash-only lookup.
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The linear search fallback is always
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disabled, ignoring the on-disk flag.
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compat Enables the linear search fallback for
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compatibility with directory entries
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created by older kernel that used a
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different case-folding algorithm.
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This mode ignores the on-disk flag.
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auto F2FS determines the mode based on the
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on-disk `SB_ENC_NO_COMPAT_FALLBACK_FL`
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flag.
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================== ========================================
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======================== ============================================================
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Debugfs Entries
+16
-1
fs/f2fs/dir.c
+16
-1
fs/f2fs/dir.c
···
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#include "xattr.h"
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#include <trace/events/f2fs.h>
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static inline bool f2fs_should_fallback_to_linear(struct inode *dir)
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{
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struct f2fs_sb_info *sbi = F2FS_I_SB(dir);
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+
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switch (F2FS_OPTION(sbi).lookup_mode) {
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case LOOKUP_PERF:
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return false;
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case LOOKUP_COMPAT:
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return true;
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case LOOKUP_AUTO:
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return !sb_no_casefold_compat_fallback(sbi->sb);
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}
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return false;
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}
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+
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#if IS_ENABLED(CONFIG_UNICODE)
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extern struct kmem_cache *f2fs_cf_name_slab;
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#endif
···
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out:
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#if IS_ENABLED(CONFIG_UNICODE)
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-
if (!sb_no_casefold_compat_fallback(dir->i_sb) &&
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if (f2fs_should_fallback_to_linear(dir) &&
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IS_CASEFOLDED(dir) && !de && use_hash) {
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use_hash = false;
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goto start_find_entry;
+7
fs/f2fs/f2fs.h
+7
fs/f2fs/f2fs.h
···
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int compress_mode; /* compression mode */
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unsigned char extensions[COMPRESS_EXT_NUM][F2FS_EXTENSION_LEN]; /* extensions */
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unsigned char noextensions[COMPRESS_EXT_NUM][F2FS_EXTENSION_LEN]; /* extensions */
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unsigned int lookup_mode;
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};
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#define F2FS_FEATURE_ENCRYPT 0x00000001
···
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FOREGROUND,
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MAX_CALL_TYPE,
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TOTAL_CALL = FOREGROUND,
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};
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enum f2fs_lookup_mode {
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LOOKUP_PERF,
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LOOKUP_COMPAT,
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LOOKUP_AUTO,
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};
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static inline int f2fs_test_bit(unsigned int nr, char *addr);
+25
fs/f2fs/super.c
+25
fs/f2fs/super.c
···
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Opt_nat_bits,
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Opt_jqfmt,
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Opt_checkpoint,
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Opt_lookup_mode,
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Opt_err,
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};
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···
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{}
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};
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static const struct constant_table f2fs_param_lookup_mode[] = {
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{"perf", LOOKUP_PERF},
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{"compat", LOOKUP_COMPAT},
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{"auto", LOOKUP_AUTO},
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{}
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};
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static const struct fs_parameter_spec f2fs_param_specs[] = {
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fsparam_enum("background_gc", Opt_gc_background, f2fs_param_background_gc),
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fsparam_flag("disable_roll_forward", Opt_disable_roll_forward),
···
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fsparam_enum("memory", Opt_memory_mode, f2fs_param_memory_mode),
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fsparam_flag("age_extent_cache", Opt_age_extent_cache),
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fsparam_enum("errors", Opt_errors, f2fs_param_errors),
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fsparam_enum("lookup_mode", Opt_lookup_mode, f2fs_param_lookup_mode),
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{}
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};
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···
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#define F2FS_SPEC_discard_unit (1 << 21)
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#define F2FS_SPEC_memory_mode (1 << 22)
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#define F2FS_SPEC_errors (1 << 23)
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#define F2FS_SPEC_lookup_mode (1 << 24)
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struct f2fs_fs_context {
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struct f2fs_mount_info info;
···
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case Opt_nat_bits:
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ctx_set_opt(ctx, F2FS_MOUNT_NAT_BITS);
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break;
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case Opt_lookup_mode:
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F2FS_CTX_INFO(ctx).lookup_mode = result.uint_32;
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ctx->spec_mask |= F2FS_SPEC_lookup_mode;
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break;
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}
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return 0;
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}
···
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F2FS_OPTION(sbi).memory_mode = F2FS_CTX_INFO(ctx).memory_mode;
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if (ctx->spec_mask & F2FS_SPEC_errors)
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F2FS_OPTION(sbi).errors = F2FS_CTX_INFO(ctx).errors;
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if (ctx->spec_mask & F2FS_SPEC_lookup_mode)
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F2FS_OPTION(sbi).lookup_mode = F2FS_CTX_INFO(ctx).lookup_mode;
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f2fs_apply_compression(fc, sb);
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f2fs_apply_test_dummy_encryption(fc, sb);
···
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if (test_opt(sbi, NAT_BITS))
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seq_puts(seq, ",nat_bits");
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if (F2FS_OPTION(sbi).lookup_mode == LOOKUP_PERF)
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seq_show_option(seq, "lookup_mode", "perf");
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else if (F2FS_OPTION(sbi).lookup_mode == LOOKUP_COMPAT)
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seq_show_option(seq, "lookup_mode", "compat");
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else if (F2FS_OPTION(sbi).lookup_mode == LOOKUP_AUTO)
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seq_show_option(seq, "lookup_mode", "auto");
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+
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return 0;
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}
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···
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#endif
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f2fs_build_fault_attr(sbi, 0, 0, FAULT_ALL);
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+
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F2FS_OPTION(sbi).lookup_mode = LOOKUP_PERF;
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}
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#ifdef CONFIG_QUOTA