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Subject[PATCH, RFC] remove task_cache entirely
kernel/fork.c contains a disabled cache for task stuctures. task 
structures are placed into the task cache only if "tsk==current", and
"tsk==current" is impossible. There is even a WARN_ON against that in
__put_task_struct().

What should we do with it? I would remove it entirely - it's dead code.
Any objections?

One problem is that order-1 allocations are not cached per-cpu - what
about using kmem_cache_alloc for the stack?

--
Manfred


--- 2.5/kernel/fork.c 2003-07-13 13:15:01.000000000 +0200
+++ build-2.5/kernel/fork.c 2003-07-13 13:14:00.000000000 +0200
@@ -53,13 +53,6 @@

rwlock_t tasklist_lock __cacheline_aligned = RW_LOCK_UNLOCKED; /* outer */

-/*
- * A per-CPU task cache - this relies on the fact that
- * the very last portion of sys_exit() is executed with
- * preemption turned off.
- */
-static task_t *task_cache[NR_CPUS] __cacheline_aligned;
-
int nr_processes(void)
{
int cpu;
@@ -80,26 +73,8 @@

static void free_task(struct task_struct *tsk)
{
- /*
- * The task cache is effectively disabled right now.
- * Do we want it? The slab cache already has per-cpu
- * stuff, but the thread info (usually a order-1 page
- * allocation) doesn't.
- */
- if (tsk != current) {
- free_thread_info(tsk->thread_info);
- free_task_struct(tsk);
- } else {
- int cpu = get_cpu();
-
- tsk = task_cache[cpu];
- if (tsk) {
- free_thread_info(tsk->thread_info);
- free_task_struct(tsk);
- }
- task_cache[cpu] = current;
- put_cpu();
- }
+ free_thread_info(tsk->thread_info);
+ free_task_struct(tsk);
}

void __put_task_struct(struct task_struct *tsk)
@@ -220,25 +195,18 @@
{
struct task_struct *tsk;
struct thread_info *ti;
- int cpu = get_cpu();

prepare_to_copy(orig);

- tsk = task_cache[cpu];
- task_cache[cpu] = NULL;
- put_cpu();
- if (!tsk) {
- tsk = alloc_task_struct();
- if (!tsk)
- return NULL;
-
- ti = alloc_thread_info(tsk);
- if (!ti) {
- free_task_struct(tsk);
- return NULL;
- }
- } else
- ti = tsk->thread_info;
+ tsk = alloc_task_struct();
+ if (!tsk)
+ return NULL;
+
+ ti = alloc_thread_info(tsk);
+ if (!ti) {
+ free_task_struct(tsk);
+ return NULL;
+ }

*ti = *orig->thread_info;
*tsk = *orig;
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