Re: [PATCH 9/12] memcg allocate all page_cgroup at boot

[Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>]

On Thu, 25 Sep 2008 15:32:06 +0900, KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:
> Allocate all page_cgroup at boot and remove page_cgroup poitner
> from struct page. This patch adds an interface as
> 
>  struct page_cgroup *lookup_page_cgroup(struct page*)
> 
> All FLATMEM/DISCONTIGMEM/SPARSEMEM  and MEMORY_HOTPLUG is supported.
> 
> Remove page_cgroup pointer reduces the amount of memory by
>  - 4 bytes per PAGE_SIZE.
>  - 8 bytes per PAGE_SIZE
> if memory controller is disabled. (even if configured.)
> meta data usage of this is no problem in FLATMEM/DISCONTIGMEM.
> On SPARSEMEM, this makes mem_section[] size twice.
> 
> On usual 8GB x86-32 server, this saves 8MB of NORMAL_ZONE memory.
> On my x86-64 server with 48GB of memory, this saves 96MB of memory.
> (and uses xx kbytes for mem_section.)
> I think this reduction makes sense.
> 
> By pre-allocation, kmalloc/kfree in charge/uncharge are removed. 
> This means
>   - we're not necessary to be afraid of kmalloc faiulre.
>     (this can happen because of gfp_mask type.)
>   - we can avoid calling kmalloc/kfree.
>   - we can avoid allocating tons of small objects which can be fragmented.
>   - we can know what amount of memory will be used for this extra-lru handling.
> 
> I added printk message as
> 
> 	"allocated %ld bytes of page_cgroup"
>         "please try cgroup_disable=memory option if you don't want"
> 
> maybe enough informative for users.
> 
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> 
>  include/linux/memcontrol.h  |   11 -
>  include/linux/mm_types.h    |    4 
>  include/linux/mmzone.h      |    9 +
>  include/linux/page_cgroup.h |   90 +++++++++++++++
>  mm/Makefile                 |    2 
>  mm/memcontrol.c             |  258 ++++++++++++--------------------------------
>  mm/page_alloc.c             |   12 --
>  mm/page_cgroup.c            |  253 +++++++++++++++++++++++++++++++++++++++++++
>  8 files changed, 431 insertions(+), 208 deletions(-)
> 
> Index: mmotm-2.6.27-rc7+/mm/page_cgroup.c
> ===================================================================
> --- /dev/null
> +++ mmotm-2.6.27-rc7+/mm/page_cgroup.c
> @@ -0,0 +1,253 @@
> +#include <linux/mm.h>
> +#include <linux/mmzone.h>
> +#include <linux/bootmem.h>
> +#include <linux/bit_spinlock.h>
> +#include <linux/page_cgroup.h>
> +#include <linux/hash.h>
> +#include <linux/memory.h>
> +
> +static void __meminit
> +__init_page_cgroup(struct page_cgroup *pc, unsigned long pfn)
> +{
> +	pc->flags = 0;
> +	pc->mem_cgroup = NULL;
> +	pc->page = pfn_to_page(pfn);
> +}
> +static unsigned long total_usage = 0;
> +
> +#ifdef CONFIG_FLAT_NODE_MEM_MAP
> +
> +
> +void __init pgdat_page_cgroup_init(struct pglist_data *pgdat)
> +{
> +	pgdat->node_page_cgroup = NULL;
> +}
> +
> +struct page_cgroup *lookup_page_cgroup(struct page *page)
> +{
> +	unsigned long pfn = page_to_pfn(page);
> +	unsigned long offset;
> +	struct page_cgroup *base;
> +
> +	base = NODE_DATA(page_to_nid(nid))->node_page_cgroup;
page_to_nid(page) :)

> +	if (unlikely(!base))
> +		return NULL;
> +
> +	offset = pfn - NODE_DATA(page_to_nid(page))->node_start_pfn;
> +	return base + offset;
> +}
> +
> +static int __init alloc_node_page_cgroup(int nid)
> +{
> +	struct page_cgroup *base, *pc;
> +	unsigned long table_size;
> +	unsigned long start_pfn, nr_pages, index;
> +
> +	start_pfn = NODE_DATA(nid)->node_start_pfn;
> +	nr_pages = NODE_DATA(nid)->node_spanned_pages;
> +
> +	table_size = sizeof(struct page_cgroup) * nr_pages;
> +
> +	base = __alloc_bootmem_node_nopanic(NODE_DATA(nid),
> +			table_size, PAGE_SIZE, __pa(MAX_DMA_ADDRESS));
> +	if (!base)
> +		return -ENOMEM;
> +	for (index = 0; index < nr_pages; index++) {
> +		pc = base + index;
> +		__init_page_cgroup(pc, start_pfn + index);
> +	}
> +	NODE_DATA(nid)->node_page_cgroup = base;
> +	total_usage += table_size;
> +	return 0;
> +}
> +
> +void __init free_node_page_cgroup(int nid)
> +{
> +	unsigned long table_size;
> +	unsigned long nr_pages;
> +	struct page_cgroup *base;
> +
> +	base = NODE_DATA(nid)->node_page_cgroup;
> +	if (!base)
> +		return;
> +	nr_pages = NODE_DATA(nid)->node_spanned_pages;
> +
> +	table_size = sizeof(struct page_cgroup) * nr_pages;
> +
> +	free_bootmem_node(NODE_DATA(nid),
> +			(unsigned long)base, table_size);
> +	NODE_DATA(nid)->node_page_cgroup = NULL;
> +}
> +
Hmm, who uses this function?

(snip)

> @@ -812,49 +708,41 @@ __mem_cgroup_uncharge_common(struct page
>  
>  	if (mem_cgroup_subsys.disabled)
>  		return;
> +	/* check the condition we can know from page */
>  
> -	/*
> -	 * Check if our page_cgroup is valid
> -	 */
> -	lock_page_cgroup(page);
> -	pc = page_get_page_cgroup(page);
> -	if (unlikely(!pc))
> -		goto unlock;
> -
> -	VM_BUG_ON(pc->page != page);
> +	pc = lookup_page_cgroup(page);
> +	if (unlikely(!pc || !PageCgroupUsed(pc)))
> +		return;
> +	preempt_disable();
> +	lock_page_cgroup(pc);
> +	if (unlikely(page_mapped(page))) {
> +		unlock_page_cgroup(pc);
> +		preempt_enable();
> +		return;
> +	}
Just for clarification, in what sequence will the page be mapped here?
mem_cgroup_uncharge_page checks whether the page is mapped.

> +	ClearPageCgroupUsed(pc);
> +	unlock_page_cgroup(pc);
>  
> -	if ((ctype == MEM_CGROUP_CHARGE_TYPE_MAPPED)
> -	    && ((PageCgroupCache(pc) || page_mapped(page))))
> -		goto unlock;
> -retry:
>  	mem = pc->mem_cgroup;
>  	mz = page_cgroup_zoneinfo(pc);
> +
>  	spin_lock_irqsave(&mz->lru_lock, flags);
> -	if (ctype == MEM_CGROUP_CHARGE_TYPE_MAPPED &&
> -	    unlikely(mem != pc->mem_cgroup)) {
> -		/* MAPPED account can be done without lock_page().
> -		   Check race with mem_cgroup_move_account() */
> -		spin_unlock_irqrestore(&mz->lru_lock, flags);
> -		goto retry;
> -	}
By these changes, ctype becomes unnecessary so it can be removed.

>  	__mem_cgroup_remove_list(mz, pc);
>  	spin_unlock_irqrestore(&mz->lru_lock, flags);
> -
> -	page_assign_page_cgroup(page, NULL);
> -	unlock_page_cgroup(page);
> -
> -
> -	res_counter_uncharge(&mem->res, PAGE_SIZE);
> +	pc->mem_cgroup = NULL;
>  	css_put(&mem->css);
> +	preempt_enable();
> +	res_counter_uncharge(&mem->res, PAGE_SIZE);
>  
> -	kmem_cache_free(page_cgroup_cache, pc);
>  	return;
> -unlock:
> -	unlock_page_cgroup(page);
>  }
>  


Thanks,
Daisuke Nishimura.

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