Re: [PATCH 6/7] memcg: speed up by percpu

[Li Zefan <lizf@cn.fujitsu.com>]

KAMEZAWA Hiroyuki wrote:
> This patch adds per-cpu look up cache for get_page_cgroup().
> Works well when nearby pages are accessed continuously.
> (And it's an usual case under buddy allocator.
> 
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> 
> 
>  include/linux/page_cgroup.h |   37 +++++++++++++++++++++++++++++++++++--
>  mm/page_cgroup.c            |   26 +++++++++++++++++++++-----
>  2 files changed, 56 insertions(+), 7 deletions(-)
> 
> Index: mm-2.6.25-rc5-mm1/mm/page_cgroup.c
> ===================================================================
> --- mm-2.6.25-rc5-mm1.orig/mm/page_cgroup.c
> +++ mm-2.6.25-rc5-mm1/mm/page_cgroup.c
> @@ -17,11 +17,10 @@
>  #include <linux/memcontrol.h>
>  #include <linux/page_cgroup.h>
>  #include <linux/err.h>
> +#include <linux/interrupt.h>
>  
>  
> -
> -#define PCGRP_SHIFT	(CONFIG_CGROUP_PAGE_CGROUP_ORDER)
> -#define PCGRP_SIZE	(1 << PCGRP_SHIFT)
> +DEFINE_PER_CPU(struct page_cgroup_cache, pcpu_page_cgroup_cache);
>  
>  struct page_cgroup_head {
>  	struct page_cgroup pc[PCGRP_SIZE];
> @@ -71,6 +70,19 @@ void free_page_cgroup(struct page_cgroup
>  }
>  
>  

redundant empty line.

> +static void save_result(struct page_cgroup  *base, unsigned long idx)
> +{
> +	int hash = idx & (PAGE_CGROUP_NR_CACHE - 1);
> +	struct page_cgroup_cache *pcp;
> +	/* look up is done under preempt_disable(). then, don't call
> +	   this under interrupt(). */
> +	preempt_disable();
> +	pcp = &__get_cpu_var(pcpu_page_cgroup_cache);
> +	pcp->ents[hash].idx = idx;
> +	pcp->ents[hash].base = base;
> +	preempt_enable();
> +}
> +
>  /*
>   * Look up page_cgroup struct for struct page (page's pfn)
>   * if (allocate == true), look up and allocate new one if necessary.
> @@ -78,7 +90,7 @@ void free_page_cgroup(struct page_cgroup
>   */
>  
>  struct page_cgroup *
> -get_page_cgroup(struct page *page, gfp_t gfpmask, bool allocate)
> +__get_page_cgroup(struct page *page, gfp_t gfpmask, bool allocate)
>  {
>  	struct page_cgroup_root *root;
>  	struct page_cgroup_head *head;
> @@ -107,8 +119,12 @@ retry:
>  	head = radix_tree_lookup(&root->root_node, idx);
>  	rcu_read_unlock();
>  
> -	if (likely(head))
> +	if (likely(head)) {
> +		if (!in_interrupt())
> +			save_result(&head->pc[0], idx);
>  		return &head->pc[pfn - base_pfn];
> +	}
> +
>  	if (allocate == false)
>  		return NULL;
>  
> Index: mm-2.6.25-rc5-mm1/include/linux/page_cgroup.h
> ===================================================================
> --- mm-2.6.25-rc5-mm1.orig/include/linux/page_cgroup.h
> +++ mm-2.6.25-rc5-mm1/include/linux/page_cgroup.h
> @@ -25,6 +25,20 @@ struct page_cgroup {
>  #define PAGE_CGROUP_FLAG_ACTIVE (0x2)	/* is on active list */
>  #define PAGE_CGROUP_FLAG_MIGRATION (0x4) /* is on active list */
>  
> +/* per cpu cashing for fast access */
> +#define PAGE_CGROUP_NR_CACHE	(0x8)
> +struct page_cgroup_cache {
> +	struct {
> +		unsigned long idx;
> +		struct page_cgroup *base;
> +	} ents[PAGE_CGROUP_NR_CACHE];
> +};
> +
> +DECLARE_PER_CPU(struct page_cgroup_cache, pcpu_page_cgroup_cache);
> +
> +#define PCGRP_SHIFT	(CONFIG_CGROUP_PAGE_CGROUP_ORDER)
> +#define PCGRP_SIZE	(1 << PCGRP_SHIFT)
> +
>  /*
>   * Lookup and return page_cgroup struct.
>   * returns NULL when
> @@ -33,9 +47,28 @@ struct page_cgroup {
>   * return -ENOMEM if cannot allocate memory.
>   * If allocate==false, gfpmask will be ignored as a result.
>   */
> -
>  struct page_cgroup *
> -get_page_cgroup(struct page *page, gfp_t gfpmask, bool allocate);
> +__get_page_cgroup(struct page *page, gfp_t gfpmask, bool allocate);
> +
> +static inline struct page_cgroup *
> +get_page_cgroup(struct page *page, gfp_t gfpmask, bool allocate)

This function is too big to be inline

> +{
> +	unsigned long pfn = page_to_pfn(page);
> +	struct page_cgroup_cache *pcp;
> +	struct page_cgroup *ret;
> +	unsigned long idx = pfn >> PCGRP_SHIFT;
> +	int hnum = (idx) & (PAGE_CGROUP_NR_CACHE - 1);
> +
> +	preempt_disable();
> +	pcp = &__get_cpu_var(pcpu_page_cgroup_cache);
> +	if (pcp->ents[hnum].idx == idx && pcp->ents[hnum].base)
> +		ret = pcp->ents[hnum].base + (pfn - (idx << PCGRP_SHIFT));
> +	else
> +		ret = NULL;
> +	preempt_enable();
> +
> +	return (ret)? ret : __get_page_cgroup(page, gfpmask, allocate);
> +}
>  
>  #else
>  
> 

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