Re: [PATCH 1/7] mm: memcontrol: charge swap to cgroup2

[Kamezawa Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

On 2015/12/10 20:39, Vladimir Davydov wrote:
> In the legacy hierarchy we charge memsw, which is dubious, because:
> 
>   - memsw.limit must be >= memory.limit, so it is impossible to limit
>     swap usage less than memory usage. Taking into account the fact that
>     the primary limiting mechanism in the unified hierarchy is
>     memory.high while memory.limit is either left unset or set to a very
>     large value, moving memsw.limit knob to the unified hierarchy would
>     effectively make it impossible to limit swap usage according to the
>     user preference.
> 
>   - memsw.usage != memory.usage + swap.usage, because a page occupying
>     both swap entry and a swap cache page is charged only once to memsw
>     counter. As a result, it is possible to effectively eat up to
>     memory.limit of memory pages *and* memsw.limit of swap entries, which
>     looks unexpected.
> 
> That said, we should provide a different swap limiting mechanism for
> cgroup2.
> 
> This patch adds mem_cgroup->swap counter, which charges the actual
> number of swap entries used by a cgroup. It is only charged in the
> unified hierarchy, while the legacy hierarchy memsw logic is left
> intact.
> 
> The swap usage can be monitored using new memory.swap.current file and
> limited using memory.swap.max.
> 
> Signed-off-by: Vladimir Davydov <vdavydov@virtuozzo.com>

setting swap.max=0 will work like mlock ?

Thanks,
-Kame


> ---
>   include/linux/memcontrol.h |   1 +
>   include/linux/swap.h       |   5 ++
>   mm/memcontrol.c            | 123 +++++++++++++++++++++++++++++++++++++++++----
>   mm/shmem.c                 |   4 ++
>   mm/swap_state.c            |   5 ++
>   5 files changed, 129 insertions(+), 9 deletions(-)
> 
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index c6a5ed2f2744..993c9a26b637 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -169,6 +169,7 @@ struct mem_cgroup {
>   
>   	/* Accounted resources */
>   	struct page_counter memory;
> +	struct page_counter swap;
>   	struct page_counter memsw;
>   	struct page_counter kmem;
>   
> diff --git a/include/linux/swap.h b/include/linux/swap.h
> index 457181844b6e..f4b3ccdcba91 100644
> --- a/include/linux/swap.h
> +++ b/include/linux/swap.h
> @@ -368,11 +368,16 @@ static inline int mem_cgroup_swappiness(struct mem_cgroup *mem)
>   #endif
>   #ifdef CONFIG_MEMCG_SWAP
>   extern void mem_cgroup_swapout(struct page *page, swp_entry_t entry);
> +extern int mem_cgroup_charge_swap(struct page *page, swp_entry_t entry);
>   extern void mem_cgroup_uncharge_swap(swp_entry_t entry);
>   #else
>   static inline void mem_cgroup_swapout(struct page *page, swp_entry_t entry)
>   {
>   }
> +static inline int mem_cgroup_charge_swap(struct page *page, swp_entry_t entry)
> +{
> +	return 0;
> +}
>   static inline void mem_cgroup_uncharge_swap(swp_entry_t entry)
>   {
>   }
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 7f5c6abf5421..9d10e2819ec4 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -1212,7 +1212,7 @@ void mem_cgroup_print_oom_info(struct mem_cgroup *memcg, struct task_struct *p)
>   		pr_cont(":");
>   
>   		for (i = 0; i < MEM_CGROUP_STAT_NSTATS; i++) {
> -			if (i == MEM_CGROUP_STAT_SWAP && !do_memsw_account())
> +			if (i == MEM_CGROUP_STAT_SWAP && !do_swap_account)
>   				continue;
>   			pr_cont(" %s:%luKB", mem_cgroup_stat_names[i],
>   				K(mem_cgroup_read_stat(iter, i)));
> @@ -1248,12 +1248,15 @@ static unsigned long mem_cgroup_get_limit(struct mem_cgroup *memcg)
>   {
>   	unsigned long limit;
>   
> -	limit = memcg->memory.limit;
> +	limit = READ_ONCE(memcg->memory.limit);
>   	if (mem_cgroup_swappiness(memcg)) {
>   		unsigned long memsw_limit;
> +		unsigned long swap_limit;
>   
> -		memsw_limit = memcg->memsw.limit;
> -		limit = min(limit + total_swap_pages, memsw_limit);
> +		memsw_limit = READ_ONCE(memcg->memsw.limit);
> +		swap_limit = min(READ_ONCE(memcg->swap.limit),
> +				 (unsigned long)total_swap_pages);
> +		limit = min(limit + swap_limit, memsw_limit);
>   	}
>   	return limit;
>   }
> @@ -4226,6 +4229,7 @@ mem_cgroup_css_alloc(struct cgroup_subsys_state *parent_css)
>   		page_counter_init(&memcg->memory, NULL);
>   		memcg->high = PAGE_COUNTER_MAX;
>   		memcg->soft_limit = PAGE_COUNTER_MAX;
> +		page_counter_init(&memcg->swap, NULL);
>   		page_counter_init(&memcg->memsw, NULL);
>   		page_counter_init(&memcg->kmem, NULL);
>   	}
> @@ -4276,6 +4280,7 @@ mem_cgroup_css_online(struct cgroup_subsys_state *css)
>   		page_counter_init(&memcg->memory, &parent->memory);
>   		memcg->high = PAGE_COUNTER_MAX;
>   		memcg->soft_limit = PAGE_COUNTER_MAX;
> +		page_counter_init(&memcg->swap, &parent->swap);
>   		page_counter_init(&memcg->memsw, &parent->memsw);
>   		page_counter_init(&memcg->kmem, &parent->kmem);
>   #if defined(CONFIG_MEMCG_LEGACY_KMEM) && defined(CONFIG_INET)
> @@ -4291,6 +4296,7 @@ mem_cgroup_css_online(struct cgroup_subsys_state *css)
>   		page_counter_init(&memcg->memory, NULL);
>   		memcg->high = PAGE_COUNTER_MAX;
>   		memcg->soft_limit = PAGE_COUNTER_MAX;
> +		page_counter_init(&memcg->swap, NULL);
>   		page_counter_init(&memcg->memsw, NULL);
>   		page_counter_init(&memcg->kmem, NULL);
>   #if defined(CONFIG_MEMCG_LEGACY_KMEM) && defined(CONFIG_INET)
> @@ -5291,7 +5297,7 @@ int mem_cgroup_try_charge(struct page *page, struct mm_struct *mm,
>   		if (page->mem_cgroup)
>   			goto out;
>   
> -		if (do_memsw_account()) {
> +		if (do_swap_account) {
>   			swp_entry_t ent = { .val = page_private(page), };
>   			unsigned short id = lookup_swap_cgroup_id(ent);
>   
> @@ -5754,26 +5760,66 @@ void mem_cgroup_swapout(struct page *page, swp_entry_t entry)
>   	memcg_check_events(memcg, page);
>   }
>   
> +/*
> + * mem_cgroup_charge_swap - charge a swap entry
> + * @page: page being added to swap
> + * @entry: swap entry to charge
> + *
> + * Try to charge @entry to the memcg that @page belongs to.
> + *
> + * Returns 0 on success, -ENOMEM on failure.
> + */
> +int mem_cgroup_charge_swap(struct page *page, swp_entry_t entry)
> +{
> +	struct mem_cgroup *memcg;
> +	struct page_counter *counter;
> +	unsigned short oldid;
> +
> +	if (!cgroup_subsys_on_dfl(memory_cgrp_subsys) || !do_swap_account)
> +		return 0;
> +
> +	memcg = page->mem_cgroup;
> +
> +	/* Readahead page, never charged */
> +	if (!memcg)
> +		return 0;
> +
> +	if (!mem_cgroup_is_root(memcg) &&
> +	    !page_counter_try_charge(&memcg->swap, 1, &counter))
> +		return -ENOMEM;
> +
> +	oldid = swap_cgroup_record(entry, mem_cgroup_id(memcg));
> +	VM_BUG_ON_PAGE(oldid, page);
> +	mem_cgroup_swap_statistics(memcg, true);
> +
> +	css_get(&memcg->css);
> +	return 0;
> +}
> +
>   /**
>    * mem_cgroup_uncharge_swap - uncharge a swap entry
>    * @entry: swap entry to uncharge
>    *
> - * Drop the memsw charge associated with @entry.
> + * Drop the swap charge associated with @entry.
>    */
>   void mem_cgroup_uncharge_swap(swp_entry_t entry)
>   {
>   	struct mem_cgroup *memcg;
>   	unsigned short id;
>   
> -	if (!do_memsw_account())
> +	if (!do_swap_account)
>   		return;
>   
>   	id = swap_cgroup_record(entry, 0);
>   	rcu_read_lock();
>   	memcg = mem_cgroup_from_id(id);
>   	if (memcg) {
> -		if (!mem_cgroup_is_root(memcg))
> -			page_counter_uncharge(&memcg->memsw, 1);
> +		if (!mem_cgroup_is_root(memcg)) {
> +			if (cgroup_subsys_on_dfl(memory_cgrp_subsys))
> +				page_counter_uncharge(&memcg->swap, 1);
> +			else
> +				page_counter_uncharge(&memcg->memsw, 1);
> +		}
>   		mem_cgroup_swap_statistics(memcg, false);
>   		css_put(&memcg->css);
>   	}
> @@ -5797,6 +5843,63 @@ static int __init enable_swap_account(char *s)
>   }
>   __setup("swapaccount=", enable_swap_account);
>   
> +static u64 swap_current_read(struct cgroup_subsys_state *css,
> +			     struct cftype *cft)
> +{
> +	struct mem_cgroup *memcg = mem_cgroup_from_css(css);
> +
> +	return (u64)page_counter_read(&memcg->swap) * PAGE_SIZE;
> +}
> +
> +static int swap_max_show(struct seq_file *m, void *v)
> +{
> +	struct mem_cgroup *memcg = mem_cgroup_from_css(seq_css(m));
> +	unsigned long max = READ_ONCE(memcg->swap.limit);
> +
> +	if (max == PAGE_COUNTER_MAX)
> +		seq_puts(m, "max\n");
> +	else
> +		seq_printf(m, "%llu\n", (u64)max * PAGE_SIZE);
> +
> +	return 0;
> +}
> +
> +static ssize_t swap_max_write(struct kernfs_open_file *of,
> +			      char *buf, size_t nbytes, loff_t off)
> +{
> +	struct mem_cgroup *memcg = mem_cgroup_from_css(of_css(of));
> +	unsigned long max;
> +	int err;
> +
> +	buf = strstrip(buf);
> +	err = page_counter_memparse(buf, "max", &max);
> +	if (err)
> +		return err;
> +
> +	mutex_lock(&memcg_limit_mutex);
> +	err = page_counter_limit(&memcg->swap, max);
> +	mutex_unlock(&memcg_limit_mutex);
> +	if (err)
> +		return err;
> +
> +	return nbytes;
> +}
> +
> +static struct cftype swap_files[] = {
> +	{
> +		.name = "swap.current",
> +		.flags = CFTYPE_NOT_ON_ROOT,
> +		.read_u64 = swap_current_read,
> +	},
> +	{
> +		.name = "swap.max",
> +		.flags = CFTYPE_NOT_ON_ROOT,
> +		.seq_show = swap_max_show,
> +		.write = swap_max_write,
> +	},
> +	{ }	/* terminate */
> +};
> +
>   static struct cftype memsw_cgroup_files[] = {
>   	{
>   		.name = "memsw.usage_in_bytes",
> @@ -5828,6 +5931,8 @@ static int __init mem_cgroup_swap_init(void)
>   {
>   	if (!mem_cgroup_disabled() && really_do_swap_account) {
>   		do_swap_account = 1;
> +		WARN_ON(cgroup_add_dfl_cftypes(&memory_cgrp_subsys,
> +					       swap_files));
>   		WARN_ON(cgroup_add_legacy_cftypes(&memory_cgrp_subsys,
>   						  memsw_cgroup_files));
>   	}
> diff --git a/mm/shmem.c b/mm/shmem.c
> index 9b051115a100..659a90d8305c 100644
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -912,6 +912,9 @@ static int shmem_writepage(struct page *page, struct writeback_control *wbc)
>   	if (!swap.val)
>   		goto redirty;
>   
> +	if (mem_cgroup_charge_swap(page, swap))
> +		goto free_swap;
> +
>   	/*
>   	 * Add inode to shmem_unuse()'s list of swapped-out inodes,
>   	 * if it's not already there.  Do it now before the page is
> @@ -940,6 +943,7 @@ static int shmem_writepage(struct page *page, struct writeback_control *wbc)
>   	}
>   
>   	mutex_unlock(&shmem_swaplist_mutex);
> +free_swap:
>   	swapcache_free(swap);
>   redirty:
>   	set_page_dirty(page);
> diff --git a/mm/swap_state.c b/mm/swap_state.c
> index d783872d746c..dea39cb03967 100644
> --- a/mm/swap_state.c
> +++ b/mm/swap_state.c
> @@ -170,6 +170,11 @@ int add_to_swap(struct page *page, struct list_head *list)
>   	if (!entry.val)
>   		return 0;
>   
> +	if (mem_cgroup_charge_swap(page, entry)) {
> +		swapcache_free(entry);
> +		return 0;
> +	}
> +
>   	if (unlikely(PageTransHuge(page)))
>   		if (unlikely(split_huge_page_to_list(page, list))) {
>   			swapcache_free(entry);
>