On 2024/8/29 4:25, Andrew Morton wrote:
On Wed, 28 Aug 2024 11:49:51 +0800 Hongbo Li <lihongbo22@xxxxxxxxxx> wrote:
Anything which is calling these functions is not performance-sensitive,
so optimizing for space is preferred. An out-of-line function which
returns a const char * will achieve this?
I think this helper can achieve this. Because it is tiny enough, the
compiler will handle this like #define macro (do the replacement)
without allocating extra functional stack. On the contrary, if it is
implemented as a non-inline function, it will cause extra functional
stack when it was called every time. And it also should be implemented
in a source file (.c file), not in header file(.h file).
No, my concern is that if, for example, str_high_low() gets used in 100
.c files then we get 100 copies of the strings "high" and "low" in
vmlinux. Making str_high_low() uninlined would fix this.
At first, I didn't consider these aspects.
However a quick experiment tells me that the compiler and linker are
indeed able to perform this cross-object-file optimization:
That's very good!
Thanks,
Hongbo
--- a/fs/open.c~a
+++ a/fs/open.c
@@ -34,6 +34,8 @@
#include <linux/mnt_idmapping.h>
#include <linux/filelock.h>
+#include <linux/string_choices.h>
+
#include "internal.h"
int do_truncate(struct mnt_idmap *idmap, struct dentry *dentry,
@@ -42,6 +44,8 @@ int do_truncate(struct mnt_idmap *idmap,
int ret;
struct iattr newattrs;
+ printk("%s\n", frozzle(dentry == NULL));
+
/* Not pretty: "inode->i_size" shouldn't really be signed. But it is. */
if (length < 0)
return -EINVAL;
--- a/fs/inode.c~a
+++ a/fs/inode.c
@@ -22,6 +22,9 @@
#include <linux/iversion.h>
#include <linux/rw_hint.h>
#include <trace/events/writeback.h>
+
+#include <linux/string_helpers.h>
+
#include "internal.h"
/*
@@ -110,6 +113,8 @@ static struct inodes_stat_t inodes_stat;
static int proc_nr_inodes(const struct ctl_table *table, int write, void *buffer,
size_t *lenp, loff_t *ppos)
{
+ printk("%s\n", frozzle(table == NULL));
+
inodes_stat.nr_inodes = get_nr_inodes();
inodes_stat.nr_unused = get_nr_inodes_unused();
return proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
--- a/include/linux/string_choices.h~a
+++ a/include/linux/string_choices.h
@@ -4,6 +4,11 @@
#include <linux/types.h>
+static inline const char *frozzle(bool v)
+{
+ return v ? "frizzle" : "frazzle";
+}
+
static inline const char *str_enable_disable(bool v)
{
return v ? "enable" : "disable";
_
x1:/usr/src/25> strings vmlinux|grep frazzle
frazzle
x1:/usr/src/25>
See, only one copy!
