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Message-ID: <20260122234621.3403276-1-jim.cromie@gmail.com>
Date: Thu, 22 Jan 2026 16:46:21 -0700
From: Jim Cromie <jim.cromie@...il.com>
To: linux-kernel@...r.kernel.org
Cc: Jim Cromie <jim.cromie@...il.com>,
Luis Chamberlain <mcgrof@...nel.org>,
Petr Pavlu <petr.pavlu@...e.com>,
Daniel Gomez <da.gomez@...nel.org>,
Sami Tolvanen <samitolvanen@...gle.com>,
Aaron Tomlin <atomlin@...mlin.com>,
linux-modules@...r.kernel.org
Subject: [RFC PATCH 1/1] module: speed modprobe by adding name_crc to struct module
"modprobe foo" currently does strcmp on the name, this can be improved.
So this commit:
1. adds name_crc to struct module
2. modpost.c computes the value and
3. outputs it for "modinfo foo" to see/use.
4. adds hotpath to find_module_all()
this uses name_crc to do quick "name-check"
falls back to strcmp only to guard against collisions.
This should significantly reduce modprobe workload, and shorten module
load-time.
Since it alters struct module, its binary incompatible. This means:
1. RFC for its wide "blast radius".
2. suitable for major version bump *only*
3. it opens door for further struct module reorg, to:
a. segregate fields by "temperature"
b. pack out paholes.
c. improve cache locality (by reordering coldest on bottom)
name should be cold now.
bikeshedding is appropriate here.
NB: this isn't a substitute for CONFIG_MODULE_SIG.
It reimplements crc_le(), doesn't reuse kernel's version.
CC: Luis Chamberlain <mcgrof@...nel.org>
CC: Petr Pavlu <petr.pavlu@...e.com>
CC: Daniel Gomez <da.gomez@...nel.org>
CC: Sami Tolvanen <samitolvanen@...gle.com>
CC: Aaron Tomlin <atomlin@...mlin.com>
CC: linux-modules@...r.kernel.org
Signed-off-by: Jim Cromie <jim.cromie@...il.com>
'#' will be ignored, and an empty message aborts the commit.
---
include/linux/module.h | 15 ++++++++-------
kernel/module/main.c | 8 ++++++--
scripts/mod/modpost.c | 18 ++++++++++++++++++
scripts/mod/modpost.h | 6 +++++-
4 files changed, 37 insertions(+), 10 deletions(-)
diff --git a/include/linux/module.h b/include/linux/module.h
index d80c3ea57472..4ea6c5ae3374 100644
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -402,10 +402,18 @@ struct klp_modinfo {
struct module {
enum module_state state;
+ u32 name_hash;
/* Member of list of modules */
struct list_head list;
+ /* Sysfs stuff. */
+ struct module_kobject mkobj;
+ struct module_attribute *modinfo_attrs;
+ const char *version;
+ const char *srcversion;
+ struct kobject *holders_dir;
+
/* Unique handle for this module */
char name[MODULE_NAME_LEN];
@@ -414,13 +422,6 @@ struct module {
unsigned char build_id[BUILD_ID_SIZE_MAX];
#endif
- /* Sysfs stuff. */
- struct module_kobject mkobj;
- struct module_attribute *modinfo_attrs;
- const char *version;
- const char *srcversion;
- struct kobject *holders_dir;
-
/* Exported symbols */
const struct kernel_symbol *syms;
const u32 *crcs;
diff --git a/kernel/module/main.c b/kernel/module/main.c
index d855f43a2be3..685218b2c5ef 100644
--- a/kernel/module/main.c
+++ b/kernel/module/main.c
@@ -39,6 +39,7 @@
#include <linux/mutex.h>
#include <linux/rculist.h>
#include <linux/uaccess.h>
+#include <linux/crc32.h>
#include <asm/cacheflush.h>
#include <linux/set_memory.h>
#include <asm/mmu_context.h>
@@ -431,13 +432,16 @@ struct module *find_module_all(const char *name, size_t len,
bool even_unformed)
{
struct module *mod;
+ u32 incoming_name_hash = crc32_le(0, name, len);
list_for_each_entry_rcu(mod, &modules, list,
lockdep_is_held(&module_mutex)) {
if (!even_unformed && mod->state == MODULE_STATE_UNFORMED)
continue;
- if (strlen(mod->name) == len && !memcmp(mod->name, name, len))
- return mod;
+ if (mod->name_hash == incoming_name_hash) {
+ if (strlen(mod->name) == len && !memcmp(mod->name, name, len))
+ return mod;
+ }
}
return NULL;
}
diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
index 755b842f1f9b..ae90e0bf9330 100644
--- a/scripts/mod/modpost.c
+++ b/scripts/mod/modpost.c
@@ -21,6 +21,22 @@
#include <stdbool.h>
#include <errno.h>
+/* Local CRC32 implementation for modpost.c */
+#define CRCPOLY_LE 0xEDB88320
+
+typedef uint32_t u32;
+
+static u32 crc32_le(u32 crc, char *p, size_t len)
+{
+ int i;
+ while (len--) {
+ crc ^= *p++;
+ for (i = 0; i < 8; i++)
+ crc = (crc >> 1) ^ ((crc & 1) ? CRCPOLY_LE : 0);
+ }
+ return crc;
+}
+
#include <hash.h>
#include <hashtable.h>
#include <list.h>
@@ -1581,6 +1597,7 @@ static void read_symbols(const char *modname)
/* strip trailing .o */
mod = new_module(modname, strlen(modname) - strlen(".o"));
+ mod->name_hash = crc32_le(0, mod->name, strlen(mod->name));
/* save .no_trim_symbol section for later use */
if (info.no_trim_symbol_len) {
@@ -1834,6 +1851,7 @@ static void add_header(struct buffer *b, struct module *mod)
buf_printf(b, "#include <linux/compiler.h>\n");
buf_printf(b, "\n");
buf_printf(b, "MODULE_INFO(name, KBUILD_MODNAME);\n");
+ buf_printf(b, "MODULE_INFO(name_crc, \"0x%08x\");\n", mod->name_hash);
buf_printf(b, "\n");
buf_printf(b, "__visible struct module __this_module\n");
buf_printf(b, "__section(\".gnu.linkonce.this_module\") = {\n");
diff --git a/scripts/mod/modpost.h b/scripts/mod/modpost.h
index 2aecb8f25c87..3fc3cfd0a039 100644
--- a/scripts/mod/modpost.h
+++ b/scripts/mod/modpost.h
@@ -11,11 +11,14 @@
#include <fcntl.h>
#include <unistd.h>
#include <elf.h>
+#include <stdint.h>
#include "../../include/linux/module_symbol.h"
#include <list_types.h>
#include "elfconfig.h"
+typedef uint32_t u32;
+
/* On BSD-alike OSes elf.h defines these according to host's word size */
#undef ELF_ST_BIND
#undef ELF_ST_TYPE
@@ -126,7 +129,8 @@ struct module {
bool seen;
bool has_init;
bool has_cleanup;
- char srcversion[25];
+ char srcversion[25];
+ u32 name_hash;
// Missing namespace dependencies
struct list_head missing_namespaces;
// Actual imported namespaces
--
2.52.0
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