linux-kernel - Re: [PATCH] add extra free kbytes tunable

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Date:	Sat, 02 Mar 2013 08:10:51 +0800
From:	Simon Jeons <simon.jeons@...il.com>
To:	Hugh Dickins <hughd@...gle.com>
CC:	Johannes Weiner <hannes@...xchg.org>,
	dormando <dormando@...ia.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>,
	Seiji Aguchi <seiji.aguchi@....com>,
	Satoru Moriya <satoru.moriya@....com>,
	Randy Dunlap <rdunlap@...otime.net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"lwoodman@...hat.com" <lwoodman@...hat.com>,
	Mel Gorman <mel@....ul.ie>
Subject: Re: [PATCH] add extra free kbytes tunable

On 03/02/2013 06:33 AM, Hugh Dickins wrote:
> On Fri, 1 Mar 2013, Simon Jeons wrote:
>> On 03/01/2013 05:22 PM, Simon Jeons wrote:
>>> On 02/23/2013 01:56 AM, Johannes Weiner wrote:
>>>> Mapped file pages have to get scanned twice before they are reclaimed
>>>> because we don't have enough usage information after the first scan.
>>> It seems that just VM_EXEC mapped file pages are protected.
>>> Issue in page reclaim subsystem:
>>> static inline int page_is_file_cache(struct page *page)
>>> {
>>>      return !PageSwapBacked(page);
>>> }
>>> AFAIK, PG_swapbacked is set if anonymous page added to swap cache, and be
>>> cleaned if removed from swap cache. So anonymous pages which are reclaimed
>>> and add to swap cache won't have this flag, then they will be treated as
>> s/are/aren't
> PG_swapbacked != PG_swapcache

Oh, I see. Thanks Hugh, thanks for your patient. :)

In function __add_to_swap_cache if add to radix tree successfully will 
result in increase NR_FILE_PAGES, why? This is anonymous page instead of 
file backed page.

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