Dave Peterson <[email protected]> wrote:
>
> On Friday 14 April 2006 00:26, Andrew Morton wrote:
> > task_lock() can be used to pin a task's ->mm. To use task_lock() in
> > badness() we'd need to either
> >
> > a) nest task_lock()s. I don't know if we're doing that anywhere else,
> > but the parent->child ordering is a natural one. or
> >
> > b) take a ref on the parent's mm_struct, drop the parent's task_lock()
> > while we walk the children, then do mmput() on the parent's mm outside
> > tasklist_lock. This is probably better.
>
> Looking a bit more closely at the code, I see that
> select_bad_process() iterates over all tasks, repeatedly calling
> badness(). This would complicate option 'b' since the iteration is
> done while holding tasklist_lock. An alternative to option 'a' that
> avoids nesting task_lock()s would be to define a couple of new
> functions that might look something like this:
>
> void mmput_atomic(struct mm_struct *mm)
> {
> if (atomic_dec_and_test(&mm->mm_users)) {
> add mm to a global list of expired mm_structs
> }
> }
>
> void mmput_atomic_cleanup(void)
> {
> empty the global list of expired mm_structs and do
> cleanup stuff for each one
> }
I think that's way too elaborate.
What's wrong with this?
--- 25/mm/oom_kill.c~a Fri Apr 14 12:37:51 2006
+++ 25-akpm/mm/oom_kill.c Fri Apr 14 12:44:49 2006
@@ -47,15 +47,25 @@ int sysctl_panic_on_oom;
unsigned long badness(struct task_struct *p, unsigned long uptime)
{
unsigned long points, cpu_time, run_time, s;
- struct list_head *tsk;
+ struct mm_struct *mm;
+ struct task_struct *child;
- if (!p->mm)
+ task_lock(p);
+ mm = p->mm;
+ if (!mm) {
+ task_unlock(p);
return 0;
+ }
/*
* The memory size of the process is the basis for the badness.
*/
- points = p->mm->total_vm;
+ points = mm->total_vm;
+
+ /*
+ * After this unlock we can no longer dereference local variable `mm'
+ */
+ task_unlock(p);
/*
* Processes which fork a lot of child processes are likely
@@ -65,11 +75,11 @@ unsigned long badness(struct task_struct
* child is eating the vast majority of memory, adding only half
* to the parents will make the child our kill candidate of choice.
*/
- list_for_each(tsk, &p->children) {
- struct task_struct *chld;
- chld = list_entry(tsk, struct task_struct, sibling);
- if (chld->mm != p->mm && chld->mm)
- points += chld->mm->total_vm/2 + 1;
+ list_for_each_entry(child, &p->children, sibling) {
+ task_lock(child);
+ if (child->mm != mm && child->mm)
+ points += child->mm->total_vm/2 + 1;
+ task_unlock(child);
}
/*
_
-
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