the attached patch removes the cmpxchg from the PID allocator and replaces
it with a spinlock. This spinlock is hit only a couple of times per
bootup, so it's not a performance issue.
Ingo
--- linux/kernel/pid.c.orig Wed Sep 25 10:36:13 2002
+++ linux/kernel/pid.c Wed Sep 25 10:38:55 2002
@@ -53,6 +53,8 @@
static pidmap_t *map_limit = pidmap_array + PIDMAP_ENTRIES;
+static spinlock_t pidmap_lock __cacheline_aligned_in_smp = SPIN_LOCK_UNLOCKED;
+
inline void free_pidmap(int pid)
{
pidmap_t *map = pidmap_array + pid / BITS_PER_PAGE;
@@ -77,8 +79,13 @@
* Free the page if someone raced with us
* installing it:
*/
- if (cmpxchg(&map->page, NULL, (void *) page))
+ spin_lock(&pidmap_lock);
+ if (map->page)
free_page(page);
+ else
+ map->page = (void *)page;
+ spin_unlock(&pidmap_lock);
+
if (!map->page)
break;
}
-
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This archive was generated by hypermail 2b29 : Mon Sep 30 2002 - 22:00:22 EST