Date: Thu, 6 Nov 2008 20:25:34 +0900
From: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: "linux-mm@kvack.org" <linux-mm@kvack.org>,
       "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
       "balbir@linux.vnet.ibm.com" <balbir@linux.vnet.ibm.com>,
       "menage@google.com" <menage@google.com>, nishimura@mxp.nes.nec.co.jp
Subject: Re: [RFC][PATCH 4/6] memcg : swap cgroup
Message-Id: <20081106202534.80e5cf0a.nishimura@mxp.nes.nec.co.jp>
In-Reply-To: <20081105172141.1a12dc23.kamezawa.hiroyu@jp.fujitsu.com>
References: <20081105171637.1b393333.kamezawa.hiroyu@jp.fujitsu.com>
	<20081105172141.1a12dc23.kamezawa.hiroyu@jp.fujitsu.com>
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On Wed, 5 Nov 2008 17:21:41 +0900, KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:
> For accounting swap, we need a record per swap entry, at least.
> 
> This patch adds following function.
>   - swap_cgroup_swapon() .... called from swapon
>   - swap_cgroup_swapoff() ... called at the end of swapoff.
> 
>   - swap_cgroup_record() .... record information of swap entry.
>   - swap_cgroup_lookup() .... lookup information of swap entry.
> 
> This patch just implements "how to record information". No actual
> method for limit the usage of swap. These routine uses flat table
> to record and lookup. "wise" lookup system like radix-tree requires
> requires memory allocation at new records but swap-out is usually
> called under memory shortage (or memcg hits limit.)
> So, I used static allocation. (maybe dynamic allocation is not very
> hard but it adds additional memory allocation in memory shortage path.)
> 
> 
> Note1: In this, we use pointer to record information and this means
>       8bytes per swap entry. I think we can reduce this when we
>       create "id of cgroup" in the range of 0-65535 or 0-255.
> 
> Note2: array of swap_cgroup is allocated from HIGHMEM. maybe good for x86-32.
> 
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> 
>  include/linux/page_cgroup.h |   35 +++++++
>  mm/page_cgroup.c            |  201 ++++++++++++++++++++++++++++++++++++++++++++
>  mm/swapfile.c               |    8 +
>  3 files changed, 244 insertions(+)
> 
Is there any reason why they are defined not in memcontrol.[ch]
but in page_cgroup.[ch]?

> Index: mmotm-2.6.28-rc2+/mm/page_cgroup.c
> ===================================================================
> --- mmotm-2.6.28-rc2+.orig/mm/page_cgroup.c
> +++ mmotm-2.6.28-rc2+/mm/page_cgroup.c
> @@ -8,6 +8,8 @@
>  #include <linux/memory.h>
>  #include <linux/vmalloc.h>
>  #include <linux/cgroup.h>
> +#include <linux/swapops.h>
> +#include <linux/highmem.h>
>  
>  static void __meminit
>  __init_page_cgroup(struct page_cgroup *pc, unsigned long pfn)
> @@ -254,3 +256,202 @@ void __init pgdat_page_cgroup_init(struc
>  }
>  
>  #endif
> +
> +
> +#ifdef CONFIG_CGROUP_MEM_RES_CTLR_SWAP
> +
> +DEFINE_MUTEX(swap_cgroup_mutex);
> +struct swap_cgroup_ctrl {
> +	spinlock_t lock;
> +	struct page **map;
> +	unsigned long length;
> +};
> +
> +struct swap_cgroup_ctrl swap_cgroup_ctrl[MAX_SWAPFILES];
> +
> +/*
> + * This 8bytes seems big..maybe we can reduce this when we can use "id" for
> + * cgroup rather than pointer.
> + */
> +struct swap_cgroup {
> +	struct mem_cgroup	*val;
> +};
> +#define SC_PER_PAGE	(PAGE_SIZE/sizeof(struct swap_cgroup))
> +#define SC_POS_MASK	(SC_PER_PAGE - 1)
> +
> +/*
> + * allocate buffer for swap_cgroup.
> + */
> +static int swap_cgroup_prepare(int type)
> +{
> +	struct page *page;
> +	struct swap_cgroup_ctrl *ctrl;
> +	unsigned long idx, max;
> +
> +	if (!do_swap_account)
> +		return 0;
> +	ctrl = &swap_cgroup_ctrl[type];
> +
> +	for (idx = 0; idx < ctrl->length; idx++) {
> +		page = alloc_page(GFP_KERNEL | __GFP_HIGHMEM | __GFP_ZERO);
> +		if (!page)
> +			goto not_enough_page;
> +		ctrl->map[idx] = page;
> +	}
> +	return 0;
> +not_enough_page:
> +	max = idx;
> +	for (idx = 0; idx < max; idx++)
> +		__free_page(ctrl->map[idx]);
> +
> +	return -ENOMEM;
> +}
> +
> +/**
> + * swap_cgroup_record - record mem_cgroup for this swp_entry.
> + * @ent: swap entry to be recorded into
> + * @mem: mem_cgroup to be recorded
> + *
> + * Returns old value at success, NULL at failure.
> + * (Of course, old value can be NULL.)
> + */
> +struct mem_cgroup *swap_cgroup_record(swp_entry_t ent, struct mem_cgroup *mem)
> +{
> +	unsigned long flags;
> +	int type = swp_type(ent);
> +	unsigned long offset = swp_offset(ent);
> +	unsigned long idx = offset / SC_PER_PAGE;
> +	unsigned long pos = offset & SC_POS_MASK;
> +	struct swap_cgroup_ctrl *ctrl;
> +	struct page *mappage;
> +	struct swap_cgroup *sc;
> +	struct mem_cgroup *old;
> +
> +	if (!do_swap_account)
> +		return NULL;
> +
> +	ctrl = &swap_cgroup_ctrl[type];
> +
> +	mappage = ctrl->map[idx];
> +	spin_lock_irqsave(&ctrl->lock, flags);
> +	sc = kmap_atomic(mappage, KM_USER0);
> +	sc += pos;
> +	old = sc->val;
> +	sc->val = mem;
> +	kunmap_atomic(mappage, KM_USER0);
> +	spin_unlock_irqrestore(&ctrl->lock, flags);
> +	return old;
> +}
> +
> +/**
> + * lookup_swap_cgroup - lookup mem_cgroup tied to swap entry
> + * @ent: swap entry to be looked up.
> + *
> + * Returns pointer to mem_cgroup at success. NULL at failure.
> + */
> +struct mem_cgroup *lookup_swap_cgroup(swp_entry_t ent)
> +{
> +	int type = swp_type(ent);
> +	unsigned long flags;
> +	unsigned long offset = swp_offset(ent);
> +	unsigned long idx = offset / SC_PER_PAGE;
> +	unsigned long pos = offset & SC_POS_MASK;
> +	struct swap_cgroup_ctrl *ctrl;
> +	struct page *mappage;
> +	struct swap_cgroup *sc;
> +	struct mem_cgroup *ret;
> +
> +	if (!do_swap_account)
> +		return NULL;
> +
> +	ctrl = &swap_cgroup_ctrl[type];
> +
> +	mappage = ctrl->map[idx];
> +
> +	spin_lock_irqsave(&ctrl->lock, flags);
> +	sc = kmap_atomic(mappage, KM_USER0);
> +	sc += pos;
> +	ret = sc->val;
> +	kunmap_atomic(mapppage, KM_USER0);
> +	spin_unlock_irqrestore(&ctrl->lock, flags);
> +	return ret;
> +}
> +
> +int swap_cgroup_swapon(int type, unsigned long max_pages)
> +{
> +	void *array;
> +	unsigned long array_size;
> +	unsigned long length;
> +	struct swap_cgroup_ctrl *ctrl;
> +
> +	if (!do_swap_account)
> +		return 0;
> +
> +	length = ((max_pages/SC_PER_PAGE) + 1);
> +	array_size = length * sizeof(void *);
> +
> +	array = vmalloc(array_size);
> +	if (!array)
> +		goto nomem;
> +
> +	memset(array, 0, array_size);
> +	ctrl = &swap_cgroup_ctrl[type];
> +	mutex_lock(&swap_cgroup_mutex);
> +	ctrl->length = length;
> +	ctrl->map = array;
> +	if (swap_cgroup_prepare(type)) {
> +		/* memory shortage */
> +		ctrl->map = NULL;
> +		ctrl->length = 0;
> +		vfree(array);
> +		mutex_unlock(&swap_cgroup_mutex);
> +		goto nomem;
> +	}
> +	mutex_unlock(&swap_cgroup_mutex);
> +
> +	printk(KERN_INFO
> +		"swap_cgroup: uses %ld bytes vmalloc and %ld bytes buffres\n",
> +		array_size, length * PAGE_SIZE);
> +	printk(KERN_INFO
> +	"swap_cgroup can be disabled by noswapaccount boot option.\n");
> +
> +	return 0;
> +nomem:
> +	printk(KERN_INFO "couldn't allocate enough memory for swap_cgroup.\n");
> +	printk(KERN_INFO
> +		"swap_cgroup can be disabled by noswapaccount boot option\n");
> +	return -ENOMEM;
> +}
> +
> +void swap_cgroup_swapoff(int type)
> +{
> +	int i;
> +	struct swap_cgroup_ctrl *ctrl;
> +
> +	if (!do_swap_account)
> +		return;
> +
> +	mutex_lock(&swap_cgroup_mutex);
> +	if (ctrl->map) {
> +		ctrl = &swap_cgroup_ctrl[type];
This line should be before "if (ctrl->map)"(otherwise "ctrl" will be undefined!).


Thanks,
Daisuke Nishimura.

> +		for (i = 0; i < ctrl->length; i++) {
> +			struct page *page = ctrl->map[i];
> +			if (page)
> +				__free_page(page);
> +		}
> +		vfree(ctrl->map);
> +		ctrl->map = NULL;
> +		ctrl->length = 0;
> +	}
> +	mutex_unlock(&swap_cgroup_mutex);
> +}
> +
> +static int __init swap_cgroup_init(void)
> +{
> +	int i;
> +	for (i = 0; i < MAX_SWAPFILES; i++)
> +		spin_lock_init(&swap_cgroup_ctrl[i].lock);
> +	return 0;
> +}
> +late_initcall(swap_cgroup_init);
> +#endif
> Index: mmotm-2.6.28-rc2+/include/linux/page_cgroup.h
> ===================================================================
> --- mmotm-2.6.28-rc2+.orig/include/linux/page_cgroup.h
> +++ mmotm-2.6.28-rc2+/include/linux/page_cgroup.h
> @@ -105,4 +105,39 @@ static inline void page_cgroup_init(void
>  }
>  
>  #endif
> +
> +#ifdef CONFIG_CGROUP_MEM_RES_CTLR_SWAP
> +#include <linux/swap.h>
> +extern struct mem_cgroup *
> +swap_cgroup_record(swp_entry_t ent, struct mem_cgroup *mem);
> +extern struct mem_cgroup *lookup_swap_cgroup(swp_entry_t ent);
> +extern int swap_cgroup_swapon(int type, unsigned long max_pages);
> +extern void swap_cgroup_swapoff(int type);
> +#else
> +#include <linux/swap.h>
> +
> +static inline
> +struct mem_cgroup *swap_cgroup_record(swp_entry_t ent, struct mem_cgroup *mem)
> +{
> +	return NULL;
> +}
> +
> +static inline
> +struct mem_cgroup *lookup_swap_cgroup(swp_entry_t ent)
> +{
> +	return NULL;
> +}
> +
> +static inline int
> +swap_cgroup_swapon(int type, unsigned long max_pages)
> +{
> +	return 0;
> +}
> +
> +static inline void swap_cgroup_swapoff(int type)
> +{
> +	return;
> +}
> +
> +#endif
>  #endif
> Index: mmotm-2.6.28-rc2+/mm/swapfile.c
> ===================================================================
> --- mmotm-2.6.28-rc2+.orig/mm/swapfile.c
> +++ mmotm-2.6.28-rc2+/mm/swapfile.c
> @@ -32,6 +32,7 @@
>  #include <asm/pgtable.h>
>  #include <asm/tlbflush.h>
>  #include <linux/swapops.h>
> +#include <linux/page_cgroup.h>
>  
>  static DEFINE_SPINLOCK(swap_lock);
>  static unsigned int nr_swapfiles;
> @@ -1345,6 +1346,9 @@ asmlinkage long sys_swapoff(const char _
>  	spin_unlock(&swap_lock);
>  	mutex_unlock(&swapon_mutex);
>  	vfree(swap_map);
> +	/* Destroy swap account informatin */
> +	swap_cgroup_swapoff(type);
> +
>  	inode = mapping->host;
>  	if (S_ISBLK(inode->i_mode)) {
>  		struct block_device *bdev = I_BDEV(inode);
> @@ -1669,6 +1673,10 @@ asmlinkage long sys_swapon(const char __
>  		nr_good_pages = swap_header->info.last_page -
>  				swap_header->info.nr_badpages -
>  				1 /* header page */;
> +
> +		if (!error)
> +			error = swap_cgroup_swapon(type, maxpages);
> +
>  		if (error)
>  			goto bad_swap;
>  	}
> 
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