linux-kernel - Re: [PATCH -mm] vmscan: merge duplicate code in shrink_active

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Date:	Tue, 12 May 2009 09:32:48 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Wu Fengguang <fengguang.wu@...el.com>
CC:	Minchan Kim <minchan.kim@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"hannes@...xchg.org" <hannes@...xchg.org>,
	"peterz@...radead.org" <peterz@...radead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"tytso@....edu" <tytso@....edu>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"elladan@...imo.com" <elladan@...imo.com>,
	"npiggin@...e.de" <npiggin@...e.de>,
	"cl@...ux-foundation.org" <cl@...ux-foundation.org>,
	"kosaki.motohiro@...fujitsu.com" <kosaki.motohiro@...fujitsu.com>
Subject: Re: [PATCH -mm] vmscan: merge duplicate code in	shrink_active_list()

Wu Fengguang wrote:
> On Tue, May 12, 2009 at 03:26:33PM +0800, Minchan Kim wrote:
>> On Tue, 12 May 2009 10:53:19 +0800
>> Wu Fengguang <fengguang.wu@...el.com> wrote:
>>
>>> The "move pages to active list" and "move pages to inactive list"
>>> code blocks are mostly identical and can be served by a function.
>>>
>>> Thanks to Andrew Morton for pointing this out.
>>>
>>> Signed-off-by: Wu Fengguang <fengguang.wu@...el.com>
>>> ---
>>>  mm/vmscan.c |   84 ++++++++++++++++++++------------------------------
>>>  1 file changed, 35 insertions(+), 49 deletions(-)
>>>
>>> --- linux.orig/mm/vmscan.c
>>> +++ linux/mm/vmscan.c
>>> @@ -1225,6 +1225,36 @@ static inline void note_zone_scanning_pr
>>>   * But we had to alter page->flags anyway.
>>>   */
>>>  
>>> +void move_active_pages_to_lru(enum lru_list lru, struct list_head *list)
>>> +{
>>> +	unsigned long pgmoved = 0;
>>> +
>>> +	while (!list_empty(&list)) {
>>> +		page = lru_to_page(&list);
>>> +		prefetchw_prev_lru_page(page, &list, flags);
>>> +
>>> +		VM_BUG_ON(PageLRU(page));
>>> +		SetPageLRU(page);
>>> +
>>> +		VM_BUG_ON(!PageActive(page));
>>> +		if (lru < LRU_ACTIVE)
>>> +			ClearPageActive(page);
>> Arithmetic on the LRU list is not good code for redability, I think. 
>> How about adding comment? 
>>
>> if (lru < LRU_ACTIVE) /* In case of moving from active list to inactive */
>>
>> Ignore me if you think this is trivial. 
> 
> Good suggestion. Or this simple one: "we are de-activating"?

lru < LRU_ACTIVE will never be true for file pages,
either active or inactive.

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