Ok, so I don't know who is interested, but I suspect this same issue
exists in ext4 too, so I'm cc'ing various random people who have doen ext3
changes and the linux-ext4 list.
This patch fixes a 200+ byte stack usage that just didn't make any sense,
and actually improves code generation a bit. Sadly, ext3 still has a
number of other functions that have excessive stack usage:
ext3_group_add [built-in.o]: 440
ext3_get_blocks_handle [built-in.o]: 296
ext3_find_entry [built-in.o]: 296
ext3_truncate [built-in.o]: 232
ext3_get_parent [built-in.o]: 232
ext3_add_entry [built-in.o]: 216
ext3_warning [built-in.o]: 216
ext3_abort [built-in.o]: 216
ext3_error [built-in.o]: 208
...
and while ext3_get_parent was pretty high up, it's certainly not the
biggest problem.
The warning/abort/error functions, btw, are due to gcc idiocy with varargs
handling on x86-64 (it allocates stack for SSE register spilling, even
though it doesn't spill any SSE registers when in kernel mode). That's a
compiler issue. But "ext3_group_add()" and the other things up there
really are just our badness.
At least ext3_group_add() is in a rather shallow callchain. That is not
true with find_entry and friends.
Anyway, with this patch, one of them is gone, and we get rid of code like
dotdot.d_parent = child; /* confusing, isn't it! */
that is no longer relevant.
---
From: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Date: Wed Aug 27 11:26:52 2008 -0700
Subject: [ext3] Don't use 'struct dentry' for internal lookups
It's more efficient to pass down only the actual parts of the dentry that
matter: the parent inode and the name. This actually shrinks the code
size a bit:
text data bss dec hex filename
87363 1024 16 88403 15953 fs/ext3/built-in.o.old
87327 1024 16 88367 1592f fs/ext3/built-in.o.new
but more importantly, it makes it unnecessary to build up a fake 'struct
dentry' on the stack in ext3_get_parent, so that function entirely
disappears from the stack footprint list.
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
---
fs/ext3/namei.c | 68 ++++++++++++++++++++++++++----------------------------
1 files changed, 33 insertions(+), 35 deletions(-)
diff --git a/fs/ext3/namei.c b/fs/ext3/namei.c
index de13e91..ed8c60d 100644
--- a/fs/ext3/namei.c
+++ b/fs/ext3/namei.c
@@ -159,7 +159,7 @@ static void dx_set_count (struct dx_entry *entries, unsigned value);
static void dx_set_limit (struct dx_entry *entries, unsigned value);
static unsigned dx_root_limit (struct inode *dir, unsigned infosize);
static unsigned dx_node_limit (struct inode *dir);
-static struct dx_frame *dx_probe(struct dentry *dentry,
+static struct dx_frame *dx_probe(const struct qstr *d_name,
struct inode *dir,
struct dx_hash_info *hinfo,
struct dx_frame *frame,
@@ -176,8 +176,10 @@ static int ext3_htree_next_block(struct inode *dir, __u32 hash,
struct dx_frame *frame,
struct dx_frame *frames,
__u32 *start_hash);
-static struct buffer_head * ext3_dx_find_entry(struct dentry *dentry,
- struct ext3_dir_entry_2 **res_dir, int *err);
+static struct buffer_head * ext3_dx_find_entry(struct inode *dir,
+ const struct qstr *d_name,
+ struct ext3_dir_entry_2 **res_dir,
+ int *err);
static int ext3_dx_add_entry(handle_t *handle, struct dentry *dentry,
struct inode *inode);
@@ -342,7 +344,7 @@ struct stats dx_show_entries(struct dx_hash_info *hinfo, struct inode *dir,
* back to userspace.
*/
static struct dx_frame *
-dx_probe(struct dentry *dentry, struct inode *dir,
+dx_probe(const struct qstr *d_name, struct inode *dir,
struct dx_hash_info *hinfo, struct dx_frame *frame_in, int *err)
{
unsigned count, indirect;
@@ -353,8 +355,6 @@ dx_probe(struct dentry *dentry, struct inode *dir,
u32 hash;
frame->bh = NULL;
- if (dentry)
- dir = dentry->d_parent->d_inode;
if (!(bh = ext3_bread (NULL,dir, 0, 0, err)))
goto fail;
root = (struct dx_root *) bh->b_data;
@@ -370,8 +370,8 @@ dx_probe(struct dentry *dentry, struct inode *dir,
}
hinfo->hash_version = root->info.hash_version;
hinfo->seed = EXT3_SB(dir->i_sb)->s_hash_seed;
- if (dentry)
- ext3fs_dirhash(dentry->d_name.name, dentry->d_name.len, hinfo);
+ if (d_name)
+ ext3fs_dirhash(d_name->name, d_name->len, hinfo);
hash = hinfo->hash;
if (root->info.unused_flags & 1) {
@@ -645,7 +645,7 @@ int ext3_htree_fill_tree(struct file *dir_file, __u32 start_hash,
}
hinfo.hash = start_hash;
hinfo.minor_hash = 0;
- frame = dx_probe(NULL, dir_file->f_path.dentry->d_inode, &hinfo, frames, &err);
+ frame = dx_probe(NULL, dir, &hinfo, frames, &err);
if (!frame)
return err;
@@ -803,15 +803,15 @@ static inline int ext3_match (int len, const char * const name,
*/
static inline int search_dirblock(struct buffer_head * bh,
struct inode *dir,
- struct dentry *dentry,
+ const struct qstr *d_name,
unsigned long offset,
struct ext3_dir_entry_2 ** res_dir)
{
struct ext3_dir_entry_2 * de;
char * dlimit;
int de_len;
- const char *name = dentry->d_name.name;
- int namelen = dentry->d_name.len;
+ const char *name = d_name->name;
+ int namelen = d_name->len;
de = (struct ext3_dir_entry_2 *) bh->b_data;
dlimit = bh->b_data + dir->i_sb->s_blocksize;
@@ -850,7 +850,8 @@ static inline int search_dirblock(struct buffer_head * bh,
* The returned buffer_head has ->b_count elevated. The caller is expected
* to brelse() it when appropriate.
*/
-static struct buffer_head * ext3_find_entry (struct dentry *dentry,
+static struct buffer_head * ext3_find_entry (struct inode *dir,
+ const struct qstr *d_name,
struct ext3_dir_entry_2 ** res_dir)
{
struct super_block * sb;
@@ -863,16 +864,15 @@ static struct buffer_head * ext3_find_entry (struct dentry *dentry,
buffer */
int num = 0;
int nblocks, i, err;
- struct inode *dir = dentry->d_parent->d_inode;
int namelen;
*res_dir = NULL;
sb = dir->i_sb;
- namelen = dentry->d_name.len;
+ namelen = d_name->len;
if (namelen > EXT3_NAME_LEN)
return NULL;
if (is_dx(dir)) {
- bh = ext3_dx_find_entry(dentry, res_dir, &err);
+ bh = ext3_dx_find_entry(dir, d_name, res_dir, &err);
/*
* On success, or if the error was file not found,
* return. Otherwise, fall back to doing a search the
@@ -923,7 +923,7 @@ restart:
brelse(bh);
goto next;
}
- i = search_dirblock(bh, dir, dentry,
+ i = search_dirblock(bh, dir, d_name,
block << EXT3_BLOCK_SIZE_BITS(sb), res_dir);
if (i == 1) {
EXT3_I(dir)->i_dir_start_lookup = block;
@@ -957,7 +957,7 @@ cleanup_and_exit:
return ret;
}
-static struct buffer_head * ext3_dx_find_entry(struct dentry *dentry,
+static struct buffer_head * ext3_dx_find_entry(struct inode *dir, const struct qstr *d_name,
struct ext3_dir_entry_2 **res_dir, int *err)
{
struct super_block * sb;
@@ -968,14 +968,13 @@ static struct buffer_head * ext3_dx_find_entry(struct dentry *dentry,
struct buffer_head *bh;
unsigned long block;
int retval;
- int namelen = dentry->d_name.len;
- const u8 *name = dentry->d_name.name;
- struct inode *dir = dentry->d_parent->d_inode;
+ int namelen = d_name->len;
+ const u8 *name = d_name->name;
sb = dir->i_sb;
/* NFS may look up ".." - look at dx_root directory block */
if (namelen > 2 || name[0] != '.'||(name[1] != '.' && name[1] != '\0')){
- if (!(frame = dx_probe(dentry, NULL, &hinfo, frames, err)))
+ if (!(frame = dx_probe(d_name, dir, &hinfo, frames, err)))
return NULL;
} else {
frame = frames;
@@ -1036,7 +1035,7 @@ static struct dentry *ext3_lookup(struct inode * dir, struct dentry *dentry, str
if (dentry->d_name.len > EXT3_NAME_LEN)
return ERR_PTR(-ENAMETOOLONG);
- bh = ext3_find_entry(dentry, &de);
+ bh = ext3_find_entry(dir, &dentry->d_name, &de);
inode = NULL;
if (bh) {
unsigned long ino = le32_to_cpu(de->inode);
@@ -1059,15 +1058,14 @@ struct dentry *ext3_get_parent(struct dentry *child)
unsigned long ino;
struct dentry *parent;
struct inode *inode;
- struct dentry dotdot;
+ static const struct qstr dotdot = {
+ .name = "..",
+ .len = 2,
+ };
struct ext3_dir_entry_2 * de;
struct buffer_head *bh;
- dotdot.d_name.name = "..";
- dotdot.d_name.len = 2;
- dotdot.d_parent = child; /* confusing, isn't it! */
-
- bh = ext3_find_entry(&dotdot, &de);
+ bh = ext3_find_entry(child->d_inode, &dotdot, &de);
inode = NULL;
if (!bh)
return ERR_PTR(-ENOENT);
@@ -1503,7 +1501,7 @@ static int ext3_dx_add_entry(handle_t *handle, struct dentry *dentry,
struct ext3_dir_entry_2 *de;
int err;
- frame = dx_probe(dentry, NULL, &hinfo, frames, &err);
+ frame = dx_probe(&dentry->d_name, dir, &hinfo, frames, &err);
if (!frame)
return err;
entries = frame->entries;
@@ -2056,7 +2054,7 @@ static int ext3_rmdir (struct inode * dir, struct dentry *dentry)
return PTR_ERR(handle);
retval = -ENOENT;
- bh = ext3_find_entry (dentry, &de);
+ bh = ext3_find_entry(dir, &dentry->d_name, &de);
if (!bh)
goto end_rmdir;
@@ -2118,7 +2116,7 @@ static int ext3_unlink(struct inode * dir, struct dentry *dentry)
handle->h_sync = 1;
retval = -ENOENT;
- bh = ext3_find_entry (dentry, &de);
+ bh = ext3_find_entry(dir, &dentry->d_name, &de);
if (!bh)
goto end_unlink;
@@ -2276,7 +2274,7 @@ static int ext3_rename (struct inode * old_dir, struct dentry *old_dentry,
if (IS_DIRSYNC(old_dir) || IS_DIRSYNC(new_dir))
handle->h_sync = 1;
- old_bh = ext3_find_entry (old_dentry, &old_de);
+ old_bh = ext3_find_entry(old_dir, &old_dentry->d_name, &old_de);
/*
* Check for inode number is _not_ due to possible IO errors.
* We might rmdir the source, keep it as pwd of some process
@@ -2289,7 +2287,7 @@ static int ext3_rename (struct inode * old_dir, struct dentry *old_dentry,
goto end_rename;
new_inode = new_dentry->d_inode;
- new_bh = ext3_find_entry (new_dentry, &new_de);
+ new_bh = ext3_find_entry(new_dir, &new_dentry->d_name, &new_de);
if (new_bh) {
if (!new_inode) {
brelse (new_bh);
@@ -2355,7 +2353,7 @@ static int ext3_rename (struct inode * old_dir, struct dentry *old_dentry,
struct buffer_head *old_bh2;
struct ext3_dir_entry_2 *old_de2;
- old_bh2 = ext3_find_entry(old_dentry, &old_de2);
+ old_bh2 = ext3_find_entry(old_dir, &old_dentry->d_name, &old_de2);
if (old_bh2) {
retval = ext3_delete_entry(handle, old_dir,
old_de2, old_bh2);
--
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