[Devel] Re: [RFC][PATCH 2/7] RSS controller core

[Balbir Singh]

Pavel Emelianov wrote:
> This includes setup of RSS container within generic
> process containers, all the declarations used in RSS
> accounting, and core code responsible for accounting.
> 
> 
> ------------------------------------------------------------------------
> 
> diff -upr linux-2.6.20.orig/include/linux/rss_container.h linux-2.6.20-0/include/linux/rss_container.h
> --- linux-2.6.20.orig/include/linux/rss_container.h	2007-03-06 13:39:17.000000000 +0300
> +++ linux-2.6.20-0/include/linux/rss_container.h	2007-03-06 13:33:28.000000000 +0300
> @@ -0,0 +1,68 @@
> +#ifndef __RSS_CONTAINER_H__
> +#define __RSS_CONTAINER_H__
> +/*
> + * RSS container
> + *
> + * Copyright 2007 OpenVZ SWsoft Inc
> + *
> + * Author: Pavel Emelianov <xemul at openvz.org>
> + *
> + */
> +
> +struct page_container;
> +struct rss_container;
> +
> +#ifdef CONFIG_RSS_CONTAINER
> +int container_rss_prepare(struct page *, struct vm_area_struct *vma,
> +		struct page_container **);
> +
> +void container_rss_add(struct page_container *);
> +void container_rss_del(struct page_container *);
> +void container_rss_release(struct page_container *);
> +
> +int mm_init_container(struct mm_struct *mm, struct task_struct *tsk);
> +void mm_free_container(struct mm_struct *mm);
> +
> +unsigned long container_isolate_pages(unsigned long nr_to_scan,
> +		struct rss_container *rss, struct list_head *dst,
> +		int active, unsigned long *scanned);
> +unsigned long container_nr_physpages(struct rss_container *rss);
> +
> +unsigned long container_try_to_free_pages(struct rss_container *);
> +void container_out_of_memory(struct rss_container *);
> +
> +void container_rss_init_early(void);
> +#else
> +static inline int container_rss_prepare(struct page *pg,
> +		struct vm_area_struct *vma, struct page_container **pc)
> +{
> +	*pc = NULL; /* to make gcc happy */
> +	return 0;
> +}
> +
> +static inline void container_rss_add(struct page_container *pc)
> +{
> +}
> +
> +static inline void container_rss_del(struct page_container *pc)
> +{
> +}
> +
> +static inline void container_rss_release(struct page_container *pc)
> +{
> +}
> +
> +static inline int mm_init_container(struct mm_struct *mm, struct task_struct *t)
> +{
> +	return 0;
> +}
> +
> +static inline void mm_free_container(struct mm_struct *mm)
> +{
> +}
> +
> +static inline void container_rss_init_early(void)
> +{
> +}
> +#endif
> +#endif
> diff -upr linux-2.6.20.orig/init/Kconfig linux-2.6.20-0/init/Kconfig
> --- linux-2.6.20.orig/init/Kconfig	2007-03-06 13:33:28.000000000 +0300
> +++ linux-2.6.20-0/init/Kconfig	2007-03-06 13:33:28.000000000 +0300
> @@ -265,6 +265,13 @@ config CPUSETS
>  	bool
>  	select CONTAINERS
> 
> +config RSS_CONTAINER
> +	bool "RSS accounting container"
> +	select RESOURCE_COUNTERS
> +	help
> +	  Provides a simple Resource Controller for monitoring and
> +	  controlling the total Resident Set Size of the tasks in a container
> +

The wording looks very familiar :-). It would be useful to add
"The reclaim logic is now container aware, when the container goes overlimit
the page reclaimer reclaims pages belonging to this container. If we are
unable to reclaim enough pages to satisfy the request, the process is
killed with an out of memory warning"

>  config SYSFS_DEPRECATED
>  	bool "Create deprecated sysfs files"
>  	default y
> diff -upr linux-2.6.20.orig/mm/Makefile linux-2.6.20-0/mm/Makefile
> --- linux-2.6.20.orig/mm/Makefile	2007-02-04 21:44:54.000000000 +0300
> +++ linux-2.6.20-0/mm/Makefile	2007-03-06 13:33:28.000000000 +0300
> @@ -29,3 +29,5 @@ obj-$(CONFIG_MEMORY_HOTPLUG) += memory_h
>  obj-$(CONFIG_FS_XIP) += filemap_xip.o
>  obj-$(CONFIG_MIGRATION) += migrate.o
>  obj-$(CONFIG_SMP) += allocpercpu.o
> +
> +obj-$(CONFIG_RSS_CONTAINER) += rss_container.o
> diff -upr linux-2.6.20.orig/mm/rss_container.c linux-2.6.20-0/mm/rss_container.c
> --- linux-2.6.20.orig/mm/rss_container.c	2007-03-06 13:39:17.000000000 +0300
> +++ linux-2.6.20-0/mm/rss_container.c	2007-03-06 13:33:28.000000000 +0300
> @@ -0,0 +1,307 @@
> +/*
> + * RSS accounting container
> + *
> + * Copyright 2007 OpenVZ SWsoft Inc
> + *
> + * Author: Pavel Emelianov <xemul at openvz.org>
> + *
> + */
> +
> +#include <linux/list.h>
> +#include <linux/sched.h>
> +#include <linux/mm.h>
> +#include <linux/res_counter.h>
> +#include <linux/rss_container.h>
> +
> +static struct container_subsys rss_subsys;
> +
> +struct rss_container {
> +	struct res_counter res;
> +	struct list_head page_list;
> +	struct container_subsys_state css;
> +};
> +
> +struct page_container {
> +	struct page *page;
> +	struct rss_container *cnt;
> +	struct list_head list;
> +};
> +

Yes, this is what I was planning to get to -- a per container LRU list.
But you have just one list, don't you need active and inactive lists?
When the global LRU is manipulated, shouldn't this list be updated as
well, so that reclaim will pick the best pages.

> +static inline struct rss_container *rss_from_cont(struct container *cnt)
> +{
> +	return container_of(container_subsys_state(cnt, &rss_subsys),
> +			struct rss_container, css);
> +}
> +
> +int mm_init_container(struct mm_struct *mm, struct task_struct *tsk)
> +{
> +	struct rss_container *cnt;
> +
> +	cnt = rss_from_cont(task_container(tsk, &rss_subsys));
> +	if (css_get(&cnt->css))
> +		return -EBUSY;
> +
> +	mm->rss_container = cnt;
> +	return 0;
> +}
> +
> +void mm_free_container(struct mm_struct *mm)
> +{
> +	css_put(&mm->rss_container->css);
> +}
> +
> +int container_rss_prepare(struct page *page, struct vm_area_struct *vma,
> +		struct page_container **ppc)
> +{
> +	struct rss_container *rss;
> +	struct page_container *pc;
> +
> +	rcu_read_lock();
> +	rss = rcu_dereference(vma->vm_mm->rss_container);
> +	css_get_current(&rss->css);
> +	rcu_read_unlock();
> +
> +	pc = kmalloc(sizeof(struct page_container), GFP_KERNEL);
> +	if (pc == NULL)
> +		goto out_nomem;
> +
> +	while (res_counter_charge(&rss->res, 1)) {
> +		if (container_try_to_free_pages(rss))
> +			continue;
> +

The return codes of the functions is a bit confusing, ideally
container_try_to_free_pages() should return 0 on success. Also
res_counter_charge() has a WARN_ON(1) if the limit is exceeded.
The system administrator can figure out the details from failcnt,
I suspect when the container is running close to it's limit,
dmesg will have too many WARNING messages.

How much memory do you try to reclaim in container_try_to_free_pages()?
With my patches, I was planning to export this knob to userspace with
a default value. This will help the administrator decide how much
of the working set/container LRU should be freed on reaching the limit.
I cannot find the definition of container_try_to_free_pages() in
this patch.



> +		container_out_of_memory(rss);
> +		if (test_thread_flag(TIF_MEMDIE))
> +			goto out_charge;
> +	}
> +
> +	pc->page = page;
> +	pc->cnt = rss;
> +	*ppc = pc;
> +	return 0;
> +
> +out_charge:
> +	kfree(pc);
> +out_nomem:
> +	css_put(&rss->css);
> +	return -ENOMEM;
> +}
> +
> +void container_rss_release(struct page_container *pc)
> +{
> +	struct rss_container *rss;
> +
> +	rss = pc->cnt;
> +	res_counter_uncharge(&rss->res, 1);
> +	css_put(&rss->css);
> +	kfree(pc);
> +}
> +
> +void container_rss_add(struct page_container *pc)
> +{
> +	struct page *pg;
> +	struct rss_container *rss;
> +
> +	pg = pc->page;
> +	rss = pc->cnt;
> +
> +	spin_lock(&rss->res.lock);
> +	list_add(&pc->list, &rss->page_list);

This is not good, it won't give us LRU behaviour which is
useful for determining which pages to free.

> +	spin_unlock(&rss->res.lock);
> +
> +	page_container(pg) = pc;
> +}
> +
> +void container_rss_del(struct page_container *pc)
> +{
> +	struct page *page;
> +	struct rss_container *rss;
> +
> +	page = pc->page;
> +	rss = pc->cnt;
> +
> +	spin_lock(&rss->res.lock);
> +	list_del(&pc->list);
> +	res_counter_uncharge_locked(&rss->res, 1);
> +	spin_unlock(&rss->res.lock);
> +
> +	css_put(&rss->css);
> +	kfree(pc);
> +}
> +
> +unsigned long container_isolate_pages(unsigned long nr_to_scan,
> +		struct rss_container *rss, struct list_head *dst,
> +		int active, unsigned long *scanned)
> +{
> +	unsigned long nr_taken = 0;
> +	struct page *page;
> +	struct page_container *pc;
> +	unsigned long scan;
> +	struct list_head *src;
> +	LIST_HEAD(pc_list);
> +	struct zone *z;
> +
> +	spin_lock_irq(&rss->res.lock);
> +	src = &rss->page_list;
> +

Which part of the working set are we pushing out, this looks like
we are using FIFO to determine which pages to reclaim. This needs
to be FIXED.

> +	for (scan = 0; scan < nr_to_scan && !list_empty(src); scan++) {
> +		pc = list_entry(src->prev, struct page_container, list);
> +		page = pc->page;
> +		z = page_zone(page);
> +
> +		list_move(&pc->list, &pc_list);
> +
> +		spin_lock(&z->lru_lock);
> +		if (PageLRU(page)) {
> +			if ((active && PageActive(page)) ||
> +					(!active && !PageActive(page))) {
> +				if (likely(get_page_unless_zero(page))) {
> +					ClearPageLRU(page);
> +					nr_taken++;
> +					list_move(&page->lru, dst);
> +				}
> +			}
> +		}
> +		spin_unlock(&z->lru_lock);
> +	}
> +
> +	list_splice(&pc_list, src);

This would lead to LRU churning, I would recommend using list_splice_tail()
instead. Since this code has a lot in common with isolate_lru_pages, it
would be nice to reuse the code in vmscan.c

NOTE: Code duplication is a back door for subtle bugs and solving the same
issue twice :-)

> +	spin_unlock_irq(&rss->res.lock);
> +
> +	*scanned = scan;
> +	return nr_taken;
> +}
> +
> +unsigned long container_nr_physpages(struct rss_container *rss)
> +{
> +	return rss->res.usage;
> +}
> +
> +static void rss_move_task(struct container_subsys *ss,
> +		struct container *cont,
> +		struct container *old_cont,
> +		struct task_struct *p)
> +{
> +	struct mm_struct *mm;
> +	struct rss_container *rss, *old_rss;
> +
> +	mm = get_task_mm(p);
> +	if (mm == NULL)
> +		goto out;
> +
> +	rss = rss_from_cont(cont);
> +	old_rss = rss_from_cont(old_cont);
> +	if (old_rss != mm->rss_container)
> +		goto out_put;
> +
> +	css_get_current(&rss->css);
> +	rcu_assign_pointer(mm->rss_container, rss);
> +	css_put(&old_rss->css);
> +

I see that the charges are not migrated. Is that good?
If a user could find a way of migrating his/her task from
one container to another, it could create an issue with
the user's task taking up a big chunk of the RSS limit.

Can we migrate any task or just the thread group leader.
In my patches, I allowed migration of just the thread
group leader. Imagine if you have several threads, no
matter which container they belong to, their mm gets
charged (usage will not show up in the container's usage).
This could confuse the system administrator.

> +out_put:
> +	mmput(mm);
> +out:
> +	return;
> +}
> +
> +static int rss_create(struct container_subsys *ss, struct container *cont)
> +{
> +	struct rss_container *rss;
> +
> +	rss = kzalloc(sizeof(struct rss_container), GFP_KERNEL);
> +	if (rss == NULL)
> +		return -ENOMEM;
> +
> +	res_counter_init(&rss->res);
> +	INIT_LIST_HEAD(&rss->page_list);
> +	cont->subsys[rss_subsys.subsys_id] = &rss->css;
> +	return 0;
> +}
> +
> +static void rss_destroy(struct container_subsys *ss,
> +		struct container *cont)
> +{
> +	kfree(rss_from_cont(cont));
> +}
> +
> +
> +static ssize_t rss_read(struct container *cont, struct cftype *cft,
> +		struct file *file, char __user *userbuf,
> +		size_t nbytes, loff_t *ppos)
> +{
> +	return res_counter_read(&rss_from_cont(cont)->res, cft->private,
> +			userbuf, nbytes, ppos);
> +}
> +
> +static ssize_t rss_write(struct container *cont, struct cftype *cft,
> +		struct file *file, const char __user *userbuf,
> +		size_t nbytes, loff_t *ppos)
> +{
> +	return res_counter_write(&rss_from_cont(cont)->res, cft->private,
> +			userbuf, nbytes, ppos);
> +}
> +
> +
> +static struct cftype rss_usage = {
> +	.name = "rss_usage",
> +	.private = RES_USAGE,
> +	.read = rss_read,
> +};
> +
> +static struct cftype rss_limit = {
> +	.name = "rss_limit",
> +	.private = RES_LIMIT,
> +	.read = rss_read,
> +	.write = rss_write,
> +};
> +
> +static struct cftype rss_failcnt = {
> +	.name = "rss_failcnt",
> +	.private = RES_FAILCNT,
> +	.read = rss_read,
> +};
> +
> +static int rss_populate(struct container_subsys *ss,
> +		struct container *cont)
> +{
> +	int rc;
> +
> +	if ((rc = container_add_file(cont, &rss_usage)) < 0)
> +		return rc;
> +	if ((rc = container_add_file(cont, &rss_failcnt)) < 0)
> +		return rc;
> +	if ((rc = container_add_file(cont, &rss_limit)) < 0)
> +		return rc;
> +
> +	return 0;
> +}
> +
> +static struct rss_container init_rss_container;
> +
> +static __init int rss_create_early(struct container_subsys *ss,
> +		struct container *cont)
> +{
> +	struct rss_container *rss;
> +
> +	rss = &init_rss_container;
> +	res_counter_init(&rss->res);
> +	INIT_LIST_HEAD(&rss->page_list);
> +	cont->subsys[rss_subsys.subsys_id] = &rss->css;
> +	ss->create = rss_create;
> +	return 0;
> +}
> +
> +static struct container_subsys rss_subsys = {
> +	.name = "rss",
> +	.create = rss_create_early,
> +	.destroy = rss_destroy,
> +	.populate = rss_populate,
> +	.attach = rss_move_task,
> +};
> +
> +void __init container_rss_init_early(void)
> +{
> +	container_register_subsys(&rss_subsys);
> +	init_mm.rss_container = rss_from_cont(
> +			task_container(&init_task, &rss_subsys));
> +	css_get_current(&init_mm.rss_container->css);
> +}
> 


-- 
	Warm Regards,
	Balbir Singh
	Linux Technology Center
	IBM, ISTL