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modules: Use a better scheme for refcounting

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Current refcounting for modules (done if CONFIG_MODULE_UNLOAD=y) is
using a lot of memory.

Each 'struct module' contains an [NR_CPUS] array of full cache lines.

This patch uses existing infrastructure (percpu_modalloc() &
percpu_modfree()) to allocate percpu space for the refcount storage.

Instead of wasting NR_CPUS*128 bytes (on i386), we now use
nr_cpu_ids*sizeof(local_t) bytes.

On a typical distro, where NR_CPUS=8, shiping 2000 modules, we reduce
size of module files by about 2 Mbytes. (1Kb per module)

Instead of having all refcounters in the same memory node - with TLB misses
because of vmalloc() - this new implementation permits to have better
NUMA properties, since each  CPU will use storage on its preferred node,
thanks to percpu storage.

Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Eric Dumazet 2009-02-03 13:31:36 +10:30 • committed by Linus Torvalds
parent 27421e211a
commit 720eba31f4
2 changed files with 41 additions and 19 deletions
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25
include/linux/module.h
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@ -219,11 +219,6 @@ void *__symbol_get_gpl(const char *symbol);
#endif
struct module_ref
{
local_t count;
} ____cacheline_aligned;
enum module_state
{
MODULE_STATE_LIVE,
@ -344,8 +339,11 @@ struct module
/* Destruction function. */
void (*exit)(void);
/* Reference counts */
struct module_ref ref[NR_CPUS];
#ifdef CONFIG_SMP
char *refptr;
#else
local_t ref;
#endif
#endif
};
#ifndef MODULE_ARCH_INIT
@ -395,13 +393,22 @@ void __symbol_put(const char *symbol);
#define symbol_put(x) __symbol_put(MODULE_SYMBOL_PREFIX #x)
void symbol_put_addr(void *addr);
static inline local_t *__module_ref_addr(struct module *mod, int cpu)
{
#ifdef CONFIG_SMP
return (local_t *) (mod->refptr + per_cpu_offset(cpu));
#else
return &mod->ref;
#endif
}
/* Sometimes we know we already have a refcount, and it's easier not
to handle the error case (which only happens with rmmod --wait). */
static inline void __module_get(struct module *module)
{
if (module) {
BUG_ON(module_refcount(module) == 0);
local_inc(&module->ref[get_cpu()].count);
local_inc(__module_ref_addr(module, get_cpu()));
put_cpu();
}
}
@ -413,7 +420,7 @@ static inline int try_module_get(struct module *module)
if (module) {
unsigned int cpu = get_cpu();
if (likely(module_is_live(module)))
local_inc(&module->ref[cpu].count);
local_inc(__module_ref_addr(module, cpu));
else
ret = 0;
put_cpu();