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Sat, 19 Sep 2026 08:23:12 -0700 (PDT) From: Yang Wen To: linkinjeon@kernel.org, sj1557.seo@samsung.com, chizhiling@163.com Cc: yuezhang.mo@sony.com, exfat@lists.linux.dev, linux-kernel@vger.kernel.org, Yang Wen Subject: [PATCH v5 1/3] exfat: add a Bloom filter for negative name lookups Date: Sat, 19 Sep 2026 23:22:38 +0800 Message-Id: <20260919152240.1507914-2-anmuxixixi@gmail.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20260919152240.1507914-1-anmuxixixi@gmail.com> References: <20260919152240.1507914-1-anmuxixixi@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Negative name lookups scan a directory from the beginning. Repeating this scan before creating each file makes bulk creation approach O(N^2). Add a 64 KiB per-directory Bloom filter. Build it lazily after a directory reaches 1024 on-disk entries. A definite miss skips the directory scan, while a possible match follows the normal lookup path so hash collisions cannot affect correctness. Signed-off-by: Yang Wen --- fs/exfat/dir.c | 140 ++++++++++++++++++++++++++++++++++++++++++++ fs/exfat/exfat_fs.h | 13 ++++ fs/exfat/inode.c | 1 + fs/exfat/namei.c | 6 +- fs/exfat/super.c | 1 + 5 files changed, 158 insertions(+), 3 deletions(-) diff --git a/fs/exfat/dir.c b/fs/exfat/dir.c index 46514b13bebd..0c5648e23e20 100644 --- a/fs/exfat/dir.c +++ b/fs/exfat/dir.c @@ -8,6 +8,8 @@ #include #include #include +#include +#include #include "exfat_raw.h" #include "exfat_fs.h" @@ -65,6 +67,140 @@ static int exfat_get_uniname_from_ext_entry(struct super_block *sb, return 0; } +static u32 exfat_name_filter_hash(struct super_block *sb, + const struct exfat_uni_name *name) +{ + unsigned long hash = init_name_hash(NULL); + int i; + + for (i = 0; i < name->name_len; i++) + hash = partial_name_hash(exfat_toupper(sb, name->name[i]), hash); + + return end_name_hash(hash); +} + +static void exfat_name_filter_indexes(struct super_block *sb, + const struct exfat_uni_name *name, + unsigned int indexes[3]) +{ + u32 hash = exfat_name_filter_hash(sb, name); + + indexes[0] = hash_32(hash, EXFAT_NAME_FILTER_ORDER); + indexes[1] = hash_32(hash ^ 0x9e3779b9U, EXFAT_NAME_FILTER_ORDER); + indexes[2] = hash_32(rol32(hash, 16) ^ 0x85ebca6bU, + EXFAT_NAME_FILTER_ORDER); +} + +void exfat_name_filter_free(struct inode *inode) +{ + struct exfat_inode_info *ei = EXFAT_I(inode); + + kvfree(ei->name_filter); + ei->name_filter = NULL; +} + +bool exfat_name_filter_maybe_contains(struct inode *inode, + const struct exfat_uni_name *name) +{ + struct exfat_inode_info *ei = EXFAT_I(inode); + unsigned int indexes[3]; + + if (!ei->name_filter) + return true; + + exfat_name_filter_indexes(inode->i_sb, name, indexes); + return test_bit(indexes[0], ei->name_filter) && + test_bit(indexes[1], ei->name_filter) && + test_bit(indexes[2], ei->name_filter); +} + +void exfat_name_filter_add(struct inode *inode, + const struct exfat_uni_name *name) +{ + struct exfat_inode_info *ei = EXFAT_I(inode); + unsigned int indexes[3]; + + if (!ei->name_filter) + return; + + exfat_name_filter_indexes(inode->i_sb, name, indexes); + __set_bit(indexes[0], ei->name_filter); + __set_bit(indexes[1], ei->name_filter); + __set_bit(indexes[2], ei->name_filter); +} + +/* + * Build a complete filter only after a directory becomes large enough for + * repeated negative linear lookups to matter. A filter hit is never trusted: + * it only allows definite misses to skip the on-disk scan. + */ +static void exfat_build_name_filter(struct super_block *sb, + struct exfat_inode_info *ei, + struct exfat_chain *p_dir) +{ + unsigned long *filter; + struct exfat_chain clu; + unsigned int clu_count = 0; + struct inode *inode = &ei->vfs_inode; + struct exfat_sb_info *sbi = EXFAT_SB(sb); + int i; + + if (ei->name_filter || + exfat_bytes_to_dentries(i_size_read(inode)) < + EXFAT_NAME_FILTER_MIN_DENTRIES) + return; + + filter = kvzalloc(EXFAT_NAME_FILTER_BYTES, GFP_NOFS); + if (!filter) + return; + + exfat_chain_dup(&clu, p_dir); + while (clu.dir != EXFAT_EOF_CLUSTER) { + for (i = 0; i < sbi->dentries_per_clu; i++) { + struct exfat_uni_name name = { }; + struct exfat_dentry *ep; + struct buffer_head *bh; + unsigned int type; + unsigned int indexes[3]; + int len; + + ep = exfat_get_dentry(sb, &clu, i, &bh); + if (!ep) + goto abort; + + type = exfat_get_entry_type(ep); + brelse(bh); + if (type == TYPE_UNUSED) + goto complete; + if (type != TYPE_FILE && type != TYPE_DIR) + continue; + + if (exfat_get_uniname_from_ext_entry(sb, &clu, i, name.name)) + goto abort; + for (len = 0; len <= MAX_NAME_LENGTH && name.name[len]; len++) + ; + if (!len || len > MAX_NAME_LENGTH) + goto abort; + name.name_len = len; + exfat_name_filter_indexes(sb, &name, indexes); + __set_bit(indexes[0], filter); + __set_bit(indexes[1], filter); + __set_bit(indexes[2], filter); + } + + if (exfat_chain_advance(sb, &clu, 1)) + goto abort; + if (unlikely(++clu_count > EXFAT_DATA_CLUSTER_COUNT(sbi))) + goto abort; + } + +complete: + ei->name_filter = filter; + return; +abort: + kvfree(filter); +} + /* read a directory entry from the opened directory */ static int exfat_readdir(struct inode *inode, loff_t *cpos, struct exfat_dir_entry *dir_entry) { @@ -1035,6 +1171,8 @@ int exfat_find_dir_entry(struct super_block *sb, struct exfat_inode_info *ei, if (num_entries < 0) return num_entries; + if (!exfat_name_filter_maybe_contains(&ei->vfs_inode, p_uniname)) + return -ENOENT; dentries_per_clu = sbi->dentries_per_clu; @@ -1196,6 +1334,8 @@ int exfat_find_dir_entry(struct super_block *sb, struct exfat_inode_info *ei, ei->hint_femp.count = 0; } + exfat_build_name_filter(sb, ei, p_dir); + /* initialized hint_stat */ hint_stat->clu = p_dir->dir; hint_stat->eidx = 0; diff --git a/fs/exfat/exfat_fs.h b/fs/exfat/exfat_fs.h index 41a2c7dfc479..899b276f105b 100644 --- a/fs/exfat/exfat_fs.h +++ b/fs/exfat/exfat_fs.h @@ -120,6 +120,11 @@ enum { #define DIR_CACHE_SIZE \ (DIV_ROUND_UP(ES_MAX_ENTRY_NUM << DENTRY_SIZE_BITS, SECTOR_SIZE) + 1) +#define EXFAT_NAME_FILTER_ORDER 19 +#define EXFAT_NAME_FILTER_BITS BIT(EXFAT_NAME_FILTER_ORDER) +#define EXFAT_NAME_FILTER_BYTES (EXFAT_NAME_FILTER_BITS >> 3) +#define EXFAT_NAME_FILTER_MIN_DENTRIES 1024 + /* Superblock flags */ #define EXFAT_FLAGS_SHUTDOWN 1 @@ -285,6 +290,8 @@ struct exfat_inode_info { struct exfat_hint hint_stat; /* hint for first empty entry */ struct exfat_hint_femp hint_femp; + /* Complete, in-memory Bloom filter of directory names */ + unsigned long *name_filter; spinlock_t cache_lru_lock; struct list_head cache_lru; @@ -620,6 +627,12 @@ int exfat_read_volume_label(struct super_block *sb, int exfat_write_volume_label(struct super_block *sb, struct exfat_uni_name *label); +bool exfat_name_filter_maybe_contains(struct inode *inode, + const struct exfat_uni_name *name); +void exfat_name_filter_add(struct inode *inode, + const struct exfat_uni_name *name); +void exfat_name_filter_free(struct inode *inode); + static inline int exfat_chain_advance(struct super_block *sb, struct exfat_chain *chain, unsigned int step) { diff --git a/fs/exfat/inode.c b/fs/exfat/inode.c index ccd13630187e..0d0c6f817775 100644 --- a/fs/exfat/inode.c +++ b/fs/exfat/inode.c @@ -445,6 +445,7 @@ struct inode *exfat_build_inode(struct super_block *sb, void exfat_evict_inode(struct inode *inode) { truncate_inode_pages_final(&inode->i_data); + exfat_name_filter_free(inode); if (!inode->i_nlink) { i_size_write(inode, 0); diff --git a/fs/exfat/namei.c b/fs/exfat/namei.c index 3c5746fc57d9..83ded3b52a8c 100644 --- a/fs/exfat/namei.c +++ b/fs/exfat/namei.c @@ -526,6 +526,7 @@ static int exfat_add_entry(struct inode *inode, const char *path, } info->entry = dentry; + exfat_name_filter_add(inode, &uniname); info->flags = ALLOC_NO_FAT_CHAIN; info->type = type; @@ -803,7 +804,6 @@ static int exfat_unlink(struct inode *dir, struct dentry *dentry) /* update the directory entry */ exfat_remove_entries(inode, &es, ES_IDX_FILE, true); - err = exfat_put_dentry_set(&es, IS_DIRSYNC(inode)); if (err) goto unlock; @@ -958,7 +958,6 @@ static int exfat_rmdir(struct inode *dir, struct dentry *dentry) exfat_set_volume_dirty(sb); exfat_remove_entries(inode, &es, ES_IDX_FILE, true); - err = exfat_put_dentry_set(&es, IS_DIRSYNC(dir)); if (err) goto unlock; @@ -1216,6 +1215,8 @@ static int __exfat_rename(struct inode *old_parent_inode, ret = exfat_rename_file(new_parent_inode, &uni_name, ei); else ret = exfat_move_file(new_parent_inode, &uni_name, ei); + if (!ret) + exfat_name_filter_add(new_parent_inode, &uni_name); if (!ret && new_inode) { struct exfat_entry_set_cache es; @@ -1228,7 +1229,6 @@ static int __exfat_rename(struct inode *old_parent_inode, } exfat_remove_entries(new_inode, &es, ES_IDX_FILE, true); - ret = exfat_put_dentry_set(&es, IS_DIRSYNC(new_inode)); if (ret) goto del_out; diff --git a/fs/exfat/super.c b/fs/exfat/super.c index 4943cef97741..4924f0fad836 100644 --- a/fs/exfat/super.c +++ b/fs/exfat/super.c @@ -209,6 +209,7 @@ static struct inode *exfat_alloc_inode(struct super_block *sb) if (!ei) return NULL; + ei->name_filter = NULL; return &ei->vfs_inode; } -- 2.34.1