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SubjectRe: [patch -mm v2] mm: introduce oom_adj_child
Date
> On Fri, 31 Jul 2009, KOSAKI Motohiro wrote:
>
> > diff --git a/fs/proc/base.c b/fs/proc/base.c
> > index 3ce5ae9..c64499e 100644
> > --- a/fs/proc/base.c
> > +++ b/fs/proc/base.c
> > @@ -1008,7 +1008,7 @@ static ssize_t oom_adjust_read(struct file *file, char __user *buf,
> > return -ESRCH;
> > task_lock(task);
> > if (task->mm)
> > - oom_adjust = task->mm->oom_adj;
> > + oom_adjust = task->signal->oom_adj;
> > else
> > oom_adjust = OOM_DISABLE;
> > task_unlock(task);
>
> This may display a /proc/pid/oom_adj that is radically different from
> task->mm->oom_adj_cached without knowledge to userspace and you can't
> simply display task->mm>oom_adj_cached here because it gets reset on every
> write to /proc/pid/oom_adj.

Is this necessary?
different value was only happen when vfork process change oom_adj. but
vfork()ed process call exec() soon.
userland monitor program don't confuse.
Plus, if you can post any troublesome testcase, I can fix it.
this is not essential code in this patch.



> > @@ -1046,12 +1046,13 @@ static ssize_t oom_adjust_write(struct file *file, const char __user *buf,
> > put_task_struct(task);
> > return -EINVAL;
> > }
> > - if (oom_adjust < task->mm->oom_adj && !capable(CAP_SYS_RESOURCE)) {
> > + if (oom_adjust < task->signal->oom_adj && !capable(CAP_SYS_RESOURCE)) {
> > task_unlock(task);
> > put_task_struct(task);
> > return -EACCES;
> > }
> > - task->mm->oom_adj = oom_adjust;
> > + task->signal->oom_adj = oom_adjust;
> > + task->mm->oom_adj_cached = OOM_CACHE_DEFAULT;
> > task_unlock(task);
> > put_task_struct(task);
> > if (end - buffer == 0)
> > diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> > index 7acc843..f93f97f 100644
> > --- a/include/linux/mm_types.h
> > +++ b/include/linux/mm_types.h
> > @@ -240,7 +240,8 @@ struct mm_struct {
> >
> > unsigned long saved_auxv[AT_VECTOR_SIZE]; /* for /proc/PID/auxv */
> >
> > - s8 oom_adj; /* OOM kill score adjustment (bit shift) */
> > + s8 oom_adj_cached; /* mirror from signal_struct->oom_adj.
> > + in vfork case, multiple processes use the same mm. */
> >
> > cpumask_t cpu_vm_mask;
> >
> > diff --git a/include/linux/oom.h b/include/linux/oom.h
> > index a7979ba..a219480 100644
> > --- a/include/linux/oom.h
> > +++ b/include/linux/oom.h
> > @@ -3,6 +3,7 @@
> >
> > /* /proc/<pid>/oom_adj set to -17 protects from the oom-killer */
> > #define OOM_DISABLE (-17)
> > +#define OOM_CACHE_DEFAULT (15)
> > /* inclusive */
> > #define OOM_ADJUST_MIN (-16)
> > #define OOM_ADJUST_MAX 15
> > diff --git a/include/linux/sched.h b/include/linux/sched.h
> > index 3ab08e4..e10b12b 100644
> > --- a/include/linux/sched.h
> > +++ b/include/linux/sched.h
> > @@ -629,6 +629,8 @@ struct signal_struct {
> > unsigned audit_tty;
> > struct tty_audit_buf *tty_audit_buf;
> > #endif
> > +
> > + s8 oom_adj; /* OOM kill score adjustment (bit shift) */
> > };
> >
> > /* Context switch must be unlocked if interrupts are to be enabled */
>
> I don't believe oom_adj is an appropriate use of signal_struct, sorry.

Real world and life aren't so simple... and linux too.
At least, regression is definitely worst result. any other way
is better than it.


>
> > diff --git a/kernel/exit.c b/kernel/exit.c
> > index 869dc22..c741a45 100644
> > --- a/kernel/exit.c
> > +++ b/kernel/exit.c
> > @@ -688,6 +689,7 @@ static void exit_mm(struct task_struct * tsk)
> > enter_lazy_tlb(mm, current);
> > /* We don't want this task to be frozen prematurely */
> > clear_freeze_flag(tsk);
> > + mm->oom_adj_cached = OOM_CACHE_DEFAULT;
> > task_unlock(tsk);
> > mm_update_next_owner(mm);
> > mmput(mm);
>
> This is similiar to an early proposal that wanted to keep an array of
> oom_adj values for tasks attached to the mm in mm_struct. The problem is
> that you're obviously losing information about all threads attached to the
> mm any time one of the threads exits or writes to /proc/pid/oom_adj. That
> information can only be regenerated with a tasklist scan.

I agree this. but I can't imazine this darkside. Can you please explain this?
maybe, we can improve this implementaion obviously. reset at each thread exitting
is caused by my lazy and small patch preference.
a bit line adding can change this.

>
> > diff --git a/kernel/fork.c b/kernel/fork.c
> > index 9b42695..b7cb474 100644
> > --- a/kernel/fork.c
> > +++ b/kernel/fork.c
> > @@ -426,6 +427,7 @@ static struct mm_struct * mm_init(struct mm_struct * mm, struct task_struct *p)
> > init_rwsem(&mm->mmap_sem);
> > INIT_LIST_HEAD(&mm->mmlist);
> > mm->flags = (current->mm) ? current->mm->flags : default_dump_filter;
> > + mm->oom_adj_cached = OOM_CACHE_DEFAULT;
> > mm->core_state = NULL;
> > mm->nr_ptes = 0;
> > set_mm_counter(mm, file_rss, 0);
> > diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> > index 175a67a..eae2d78 100644
> > --- a/mm/oom_kill.c
> > +++ b/mm/oom_kill.c
> > @@ -58,7 +58,7 @@ unsigned long badness(struct task_struct *p, unsigned long uptime)
> > unsigned long points, cpu_time, run_time;
> > struct mm_struct *mm;
> > struct task_struct *child;
> > - int oom_adj;
> > + s8 oom_adj;
> >
> > task_lock(p);
> > mm = p->mm;
> > @@ -66,7 +66,10 @@ unsigned long badness(struct task_struct *p, unsigned long uptime)
> > task_unlock(p);
> > return 0;
> > }
> > - oom_adj = mm->oom_adj;
> > +
> > + if (mm->oom_adj_cached < p->signal->oom_adj)
> > + mm->oom_adj_cached = p->signal->oom_adj;
>
> This conditional will never be true since mm->oom_adj_cached is
> initialized to 15, which is the upper bound on which p->signal->oom_adj
> may ever be, so mm->oom_adj_cached never gets changed from
> OOM_CACHE_DEFAULT.

Ah, good catch. this condition shold be reserve. thanks.


> Thus, this patch doesn't even work, and you probably would have noticed
> that if you'd checked /proc/pid/oom_score for any pid.
>
> Even if mm->oom_adj_cached _was_ properly updated here,
> /proc/pid/oom_score would be out of sync with more negative oom_adj values
> for threads sharing the mm_struct since it calls badness() for only a
> single thread.

Hm, I don't think this is serious problem. but I can fix it easily
because badness() isn't fast-path.



>
> > + oom_adj = mm->oom_adj_cached;
> > if (oom_adj == OOM_DISABLE) {
> > task_unlock(p);
> > return 0;
> > @@ -350,7 +354,7 @@ static int oom_kill_task(struct task_struct *p)
> >
> > task_lock(p);
> > mm = p->mm;
> > - if (!mm || mm->oom_adj == OOM_DISABLE) {
> > + if (!mm || p->signal->oom_adj == OOM_DISABLE) {
> > task_unlock(p);
> > return 1;
> > }





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