Re: [PATCH] memcg: avoid unnecessary initialization

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

KAMEZAWA Hiroyuki wrote:
> An easy cut out from memcg: performance improvement patch set.
> Tested on: x86-64/linux-2.6.26-rc1-git6
> 
> Thanks,
> -Kame
> ==
> * remove over-killing initialization (in fast path)
> * makeing the condition for PAGE_CGROUP_FLAG_ACTIVE be more obvious.
> 
> Signed-off-by: KAMEAZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> 

Yes we don't need to init or del_init pc->lru.

Reviewed-by: Li Zefan <lizf@cn.fujitsu.com>

> ---
>  mm/memcontrol.c |   11 ++++++++---
>  1 file changed, 8 insertions(+), 3 deletions(-)
> 
> Index: linux-2.6.26-rc1/mm/memcontrol.c
> ===================================================================
> --- linux-2.6.26-rc1.orig/mm/memcontrol.c
> +++ linux-2.6.26-rc1/mm/memcontrol.c
> @@ -296,7 +296,7 @@ static void __mem_cgroup_remove_list(str
>  		MEM_CGROUP_ZSTAT(mz, MEM_CGROUP_ZSTAT_INACTIVE) -= 1;
>  
>  	mem_cgroup_charge_statistics(pc->mem_cgroup, pc->flags, false);
> -	list_del_init(&pc->lru);
> +	list_del(&pc->lru);
>  }
>  
>  static void __mem_cgroup_add_list(struct mem_cgroup_per_zone *mz,
> @@ -559,7 +559,7 @@ retry:
>  	}
>  	unlock_page_cgroup(page);
>  
> -	pc = kmem_cache_zalloc(page_cgroup_cache, gfp_mask);
> +	pc = kmem_cache_alloc(page_cgroup_cache, gfp_mask);
>  	if (pc == NULL)
>  		goto err;
>  
> @@ -606,9 +606,14 @@ retry:
>  	pc->ref_cnt = 1;
>  	pc->mem_cgroup = mem;
>  	pc->page = page;
> -	pc->flags = PAGE_CGROUP_FLAG_ACTIVE;
> +	/*
> +	 * If a page is accounted as a page cache, insert to inactive list.
> +	 * If anon, insert to active list.
> +	 */
>  	if (ctype == MEM_CGROUP_CHARGE_TYPE_CACHE)
>  		pc->flags = PAGE_CGROUP_FLAG_CACHE;
> +	else
> +		pc->flags = PAGE_CGROUP_FLAG_ACTIVE;
>  
>  	lock_page_cgroup(page);
>  	if (page_get_page_cgroup(page)) {
> 
> 
>