Re: [PATCH -mm 2/4] oom: select_bad_process: PF_EXITING checkshould take ->mm into account

From: Oleg Nesterov
Date: Tue Apr 06 2010 - 09:41:46 EST

On 04/06, anfei wrote:
> On Tue, Apr 06, 2010 at 02:18:11PM +0200, Oleg Nesterov wrote:
> >
> > I do not really know what is the "right" solution. Even if we fix this
> > check for mt case, we also have CLONE_VM tasks.
> >
> What about checking mm->mm_users too? If there are any other users,
> just let badness judge. CLONE_VM tasks but not mt seem rare, and
> badness doesn't consider it too.

Even if we forget about get_task_mm() which increments mm_users, it is not
clear to me how to do this check correctly.

Say, mm_users > 1 but SIGNAL_GROUP_EXIT is set. This means this process is
exiting and (ignoring CLONE_VM task) it is going to release its ->mm. But
otoh mm can be NULL.

Perhaps we can do

if ((PF_EXITING && thread_group_empty(p) ||
(p->signal->flags & SIGNAL_GROUP_EXIT) {
// OK, it is exiting

bool has_mm = false;
do {
if (t->mm) {
has_mm = true;
} while_each_thread(p, t);

if (!has_mm)

if (p != current)
return ERR_PTR(-1);

I dunno.


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