Re: [RFC v2] mm: add page preemption

[Hillf Danton <hdanton@sina.com>]

Date: Mon, 28 Oct 2019 11:56:17 -0400 Johannes Weiner wrote:
> 
> On Sat, Oct 26, 2019 at 07:28:08PM +0800, Hillf Danton wrote:
> > 
> > The cpu preemption feature makes a task able to preempt other tasks
> > of lower priorities for cpu. It has been around for a while.
> > 
> > This work introduces task prio into page reclaiming in order to add
> > the page preemption feature that makes a task able to preempt other
> > tasks of lower priorities for page.
> > 
> > No page will be reclaimed on behalf of tasks of lower priorities
> 
> ... at which point they'll declare OOM and kill the high-pri task?

Fixed. Thanks.

--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -164,6 +164,11 @@ static bool oom_unkillable_task(struct t
 		return true;
 	if (p->flags & PF_KTHREAD)
 		return true;
+
+#ifdef CONFIG_PAGE_PREEMPTION
+	if (p->prio < current->prio)
+		return true;
+#endif
 	return false;
 }
 
--


> Please have a look at the cgroup2 memory.low control. This memory
> prioritization problem has already been solved.

Scooter never runs in subway. Fixed.

--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -197,8 +198,18 @@ struct page {
 	/* Usage count. *DO NOT USE DIRECTLY*. See page_ref.h */
 	atomic_t _refcount;
 
+	/* 32/56 bytes above */
+
 #ifdef CONFIG_MEMCG
 	struct mem_cgroup *mem_cgroup;
+#else
+#ifdef CONFIG_64BIT
+	union {
+		int prio;
+		void *__pad;
+	};
+#define CONFIG_PAGE_PREEMPTION PP
+#endif
 #endif
 
 	/*
--