linux-kernel - Re: [PATCH v2] mm: add free_hot_cold_page

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Date:	Fri, 11 Nov 2011 15:19:58 +0400
From:	Konstantin Khlebnikov <khlebnikov@...nvz.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"minchan.kim@...il.com" <minchan.kim@...il.com>
Subject: Re: [PATCH v2] mm: add free_hot_cold_page_list helper

Andrew Morton wrote:
> On Tue, 01 Nov 2011 11:45:02 +0300
> Konstantin Khlebnikov<khlebnikov@...nvz.org>  wrote:
>
>> This patch adds helper free_hot_cold_page_list() to free list of 0-order pages.
>> It frees pages directly from the list without temporary page-vector.
>> It also calls trace_mm_pagevec_free() to simulate pagevec_free() behaviour.
>>
>> bloat-o-meter:
>>
>> add/remove: 1/1 grow/shrink: 1/3 up/down: 267/-295 (-28)
>> function                                     old     new   delta
>> free_hot_cold_page_list                        -     264    +264
>> get_page_from_freelist                      2129    2132      +3
>> __pagevec_free                               243     239      -4
>> split_free_page                              380     373      -7
>> release_pages                                606     510     -96
>> free_page_list                               188       -    -188
>
> Here's what you changed:
>
> --- a/mm/page_alloc.c~mm-add-free_hot_cold_page_list-helper-v2
> +++ a/mm/page_alloc.c
> @@ -1210,6 +1210,9 @@ out:
>   	local_irq_restore(flags);
>   }
>
> +/*
> + * Free a list of 0-order pages
> + */
>   void free_hot_cold_page_list(struct list_head *list, int cold)
>   {
>   	struct page *page, *next;
> @@ -1218,8 +1221,6 @@ void free_hot_cold_page_list(struct list
>   		trace_mm_pagevec_free(page, cold);
>   		free_hot_cold_page(page, cold);
>   	}
> -
> -	INIT_LIST_HEAD(list);
>   }
>
>   /*
> _
>
> However I can't find any sign that you addressed Minchin's original
> review comment regarding free_hot_cold_page_list():
>
> : I understand you want to minimize changes without breaking current ABI
> : with trace tools.
> : But apparently, It's not a pagvec_free. It just hurts readability.
> : As I take a look at the code, mm_pagevec_free isn't related to pagevec
> : but I guess it can represent 0-order pages free because 0-order pages
> : are freed only by pagevec until now.
> : So, how about renaming it with mm_page_free or mm_page_free_zero_order?
> : If you do, you need to do s/MM_PAGEVEC_FREE/MM_FREE_FREE/g in
> : trace-pagealloc-postprocess.pl.
>

Now I try to handle this, but this events logic little bit messy:
kernel always emit mm_page_free_direct event even if we free it in batch.
We really need two events for page-free? Maybe we can just remove pagevec-free and
rename page_free_direct into page_free?

BTW, pagevec_free now absolutely unused, I'll remove it in separate patch.
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