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Message-ID: <tencent_82716EB4F15F579C738C3CC3AFE62E822207@qq.com>
Date: Fri, 4 Jul 2025 10:43:57 +0800
From: Yuwen Chen <ywen.chen@...mail.com>
To: hch@...radead.org
Cc: adilger.kernel@...ger.ca,
brauner@...nel.org,
chao@...nel.org,
jaegeuk@...nel.org,
linux-ext4@...r.kernel.org,
linux-f2fs-devel@...ts.sourceforge.net,
linux-fsdevel@...r.kernel.org,
linux-kernel@...r.kernel.org,
tytso@....edu,
viro@...iv.linux.org.uk,
ywen.chen@...mail.com
Subject: [PATCH v3 1/2] libfs: reduce the number of memory allocations in generic_ci_match
During path traversal, the generic_ci_match function may be called
multiple times. The number of memory allocations and releases
in it accounts for a relatively high proportion in the flamegraph.
This patch significantly reduces the number of memory allocations
in generic_ci_match through pre - allocation.
Signed-off-by: Yuwen Chen <ywen.chen@...mail.com>
---
fs/ext4/namei.c | 2 +-
fs/f2fs/dir.c | 2 +-
fs/libfs.c | 33 ++++++++++++++++++++++++++++++---
include/linux/fs.h | 8 +++++++-
4 files changed, 39 insertions(+), 6 deletions(-)
diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
index a178ac2294895..f235693bd71aa 100644
--- a/fs/ext4/namei.c
+++ b/fs/ext4/namei.c
@@ -1443,7 +1443,7 @@ static bool ext4_match(struct inode *parent,
return generic_ci_match(parent, fname->usr_fname,
&fname->cf_name, de->name,
- de->name_len) > 0;
+ de->name_len, NULL) > 0;
}
#endif
diff --git a/fs/f2fs/dir.c b/fs/f2fs/dir.c
index c36b3b22bfffd..4c6611fbd9574 100644
--- a/fs/f2fs/dir.c
+++ b/fs/f2fs/dir.c
@@ -197,7 +197,7 @@ static inline int f2fs_match_name(const struct inode *dir,
if (fname->cf_name.name)
return generic_ci_match(dir, fname->usr_fname,
&fname->cf_name,
- de_name, de_name_len);
+ de_name, de_name_len, NULL);
#endif
f.usr_fname = fname->usr_fname;
diff --git a/fs/libfs.c b/fs/libfs.c
index 9ea0ecc325a81..d2a6b2a4fe11c 100644
--- a/fs/libfs.c
+++ b/fs/libfs.c
@@ -1863,6 +1863,26 @@ static const struct dentry_operations generic_ci_dentry_ops = {
#endif
};
+#define DECRYPTED_NAME_PREALLOC_MIN_LEN 64
+static inline char *decrypted_name_prealloc_resize(
+ struct decrypted_name_prealloc *prealloc,
+ size_t wantlen)
+{
+ char *retbuf = NULL;
+
+ if (prealloc->name && wantlen >= prealloc->namelen)
+ return prealloc->name;
+
+ retbuf = kmalloc(wantlen + DECRYPTED_NAME_PREALLOC_MIN_LEN, GFP_KERNEL);
+ if (!retbuf)
+ return NULL;
+
+ kfree(prealloc->name);
+ prealloc->name = retbuf;
+ prealloc->namelen = wantlen + DECRYPTED_NAME_PREALLOC_MIN_LEN;
+ return retbuf;
+}
+
/**
* generic_ci_match() - Match a name (case-insensitively) with a dirent.
* This is a filesystem helper for comparison with directory entries.
@@ -1873,6 +1893,7 @@ static const struct dentry_operations generic_ci_dentry_ops = {
* @folded_name: Optional pre-folded name under lookup
* @de_name: Dirent name.
* @de_name_len: dirent name length.
+ * @prealloc: decrypted name memory buffer
*
* Test whether a case-insensitive directory entry matches the filename
* being searched. If @folded_name is provided, it is used instead of
@@ -1884,7 +1905,8 @@ static const struct dentry_operations generic_ci_dentry_ops = {
int generic_ci_match(const struct inode *parent,
const struct qstr *name,
const struct qstr *folded_name,
- const u8 *de_name, u32 de_name_len)
+ const u8 *de_name, u32 de_name_len,
+ struct decrypted_name_prealloc *prealloc)
{
const struct super_block *sb = parent->i_sb;
const struct unicode_map *um = sb->s_encoding;
@@ -1899,7 +1921,11 @@ int generic_ci_match(const struct inode *parent,
if (WARN_ON_ONCE(!fscrypt_has_encryption_key(parent)))
return -EINVAL;
- decrypted_name.name = kmalloc(de_name_len, GFP_KERNEL);
+ if (!prealloc)
+ decrypted_name.name = kmalloc(de_name_len, GFP_KERNEL);
+ else
+ decrypted_name.name = decrypted_name_prealloc_resize(
+ prealloc, de_name_len);
if (!decrypted_name.name)
return -ENOMEM;
res = fscrypt_fname_disk_to_usr(parent, 0, 0, &encrypted_name,
@@ -1928,7 +1954,8 @@ int generic_ci_match(const struct inode *parent,
res = utf8_strncasecmp(um, name, &dirent);
out:
- kfree(decrypted_name.name);
+ if (!prealloc)
+ kfree(decrypted_name.name);
if (res < 0 && sb_has_strict_encoding(sb)) {
pr_err_ratelimited("Directory contains filename that is invalid UTF-8");
return 0;
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 4ec77da65f144..65307c8c11485 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -3651,10 +3651,16 @@ extern int generic_file_fsync(struct file *, loff_t, loff_t, int);
extern int generic_check_addressable(unsigned, u64);
extern void generic_set_sb_d_ops(struct super_block *sb);
+
+struct decrypted_name_prealloc {
+ char *name;
+ size_t namelen;
+};
extern int generic_ci_match(const struct inode *parent,
const struct qstr *name,
const struct qstr *folded_name,
- const u8 *de_name, u32 de_name_len);
+ const u8 *de_name, u32 de_name_len,
+ struct decrypted_name_prealloc *prealloc);
#if IS_ENABLED(CONFIG_UNICODE)
int generic_ci_d_hash(const struct dentry *dentry, struct qstr *str);
--
2.34.1
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