linux-kernel - Re: [PATCH v4 1/3] memcg: clean up existing move charge code

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Message-Id: <20120313144501.d031f25d.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Tue, 13 Mar 2012 14:45:01 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Daisuke Nishimura <nishimura@....nes.nec.co.jp>,
	Hillf Danton <dhillf@...il.com>,
	David Rientjes <rientjes@...gle.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v4 1/3] memcg: clean up existing move charge code

On Mon, 12 Mar 2012 18:30:54 -0400
Naoya Horiguchi <n-horiguchi@...jp.nec.com> wrote:

> We'll introduce the thp variant of move charge code in later patches,
> but before doing that let's start with refactoring existing code.
> Here we replace lengthy function name is_target_pte_for_mc() with
> shorter one in order to avoid ugly line breaks.
> And for better readability, we explicitly use MC_TARGET_* instead of
> simply using integers.
> 
> Signed-off-by: Naoya Horiguchi <n-horiguchi@...jp.nec.com>

Thanks.

Seems ok to me.
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...futjisu.com>

Hmm. some nitpicks.

> ---
>  mm/memcontrol.c |   20 ++++++++++----------
>  1 files changed, 10 insertions(+), 10 deletions(-)
> 
> diff --git linux-next-20120307.orig/mm/memcontrol.c linux-next-20120307/mm/memcontrol.c
> index a288855..3d16618 100644
> --- linux-next-20120307.orig/mm/memcontrol.c
> +++ linux-next-20120307/mm/memcontrol.c
> @@ -5069,7 +5069,7 @@ one_by_one:
>  }
>  
>  /**
> - * is_target_pte_for_mc - check a pte whether it is valid for move charge
> + * get_mctgt_type - get target type of moving charge
>   * @vma: the vma the pte to be checked belongs
>   * @addr: the address corresponding to the pte to be checked
>   * @ptent: the pte to be checked
> @@ -5092,7 +5092,7 @@ union mc_target {
>  };
>  
>  enum mc_target_type {
> -	MC_TARGET_NONE,	/* not used */
> +	MC_TARGET_NONE, 

How about

	MC_TARGET_NONE = 0,

Becasue you use 
	if (get_mctgt_type()) 
later.



>  	MC_TARGET_PAGE,
>  	MC_TARGET_SWAP,
>  };
> @@ -5173,12 +5173,12 @@ static struct page *mc_handle_file_pte(struct vm_area_struct *vma,
>  	return page;
>  }
>  
> -static int is_target_pte_for_mc(struct vm_area_struct *vma,
> +static enum mc_target_type get_mctgt_type(struct vm_area_struct *vma,
>  		unsigned long addr, pte_t ptent, union mc_target *target)

I admit old name is too long. But...Hm...get_mctgt_type()...how about

	move_charge_type() or
	mctgt_type() or
	mc_type() ?

I don't have good sense of naming ;(

>  {
>  	struct page *page = NULL;
>  	struct page_cgroup *pc;
> -	int ret = 0;
> +	enum mc_target_type ret = MC_TARGET_NONE;
>  	swp_entry_t ent = { .val = 0 };
>  
>  	if (pte_present(ptent))
> @@ -5189,7 +5189,7 @@ static int is_target_pte_for_mc(struct vm_area_struct *vma,
>  		page = mc_handle_file_pte(vma, addr, ptent, &ent);
>  
>  	if (!page && !ent.val)
> -		return 0;
> +		return ret;
>  	if (page) {
>  		pc = lookup_page_cgroup(page);
>  		/*
> @@ -5206,7 +5206,7 @@ static int is_target_pte_for_mc(struct vm_area_struct *vma,
>  			put_page(page);
>  	}
>  	/* There is a swap entry and a page doesn't exist or isn't charged */
> -	if (ent.val && !ret &&
> +	if (ent.val && ret != MC_TARGET_NONE &&

If you do MC_TARGET_NONE = 0 in above, using !ret seems ok to me.

>  			css_id(&mc.from->css) == lookup_swap_cgroup_id(ent)) {
>  		ret = MC_TARGET_SWAP;
>  		if (target)
> @@ -5227,7 +5227,7 @@ static int mem_cgroup_count_precharge_pte_range(pmd_t *pmd,
>  
>  	pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
>  	for (; addr != end; pte++, addr += PAGE_SIZE)
> -		if (is_target_pte_for_mc(vma, addr, *pte, NULL))
> +		if (get_mctgt_type(vma, addr, *pte, NULL))
>  			mc.precharge++;	/* increment precharge temporarily */
>  	pte_unmap_unlock(pte - 1, ptl);
>  	cond_resched();
> @@ -5397,8 +5397,8 @@ retry:
>  		if (!mc.precharge)
>  			break;
>  
> -		type = is_target_pte_for_mc(vma, addr, ptent, &target);
> -		switch (type) {
> +		target_type = get_mctgt_type(vma, addr, ptent, &target);
> +		switch (target_type) {

It 'target_type' is unused later
 
	switch(get_mctgt_type(vma, addr, ptent, &target))

is ok ?

Thanks,
-Kame

>  		case MC_TARGET_PAGE:
>  			page = target.page;
>  			if (isolate_lru_page(page))
> @@ -5411,7 +5411,7 @@ retry:
>  				mc.moved_charge++;
>  			}
>  			putback_lru_page(page);
> -put:			/* is_target_pte_for_mc() gets the page */
> +put:			/* get_mctgt_type() gets the page */
>  			put_page(page);
>  			break;
>  		case MC_TARGET_SWAP:
> -- 
> 1.7.7.6
> 
> --
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