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Date: Sat, 02 Mar 2013 08:10:51 +0800
From: Simon Jeons <simon.jeons@gmail.com>
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To: Hugh Dickins <hughd@google.com>
CC: Johannes Weiner <hannes@cmpxchg.org>, dormando <dormando@rydia.net>,
        Andrew Morton <akpm@linux-foundation.org>,
        Rik van Riel <riel@redhat.com>, Seiji Aguchi <seiji.aguchi@hds.com>,
        Satoru Moriya <satoru.moriya@hds.com>,
        Randy Dunlap <rdunlap@xenotime.net>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
        "lwoodman@redhat.com" <lwoodman@redhat.com>,
        Mel Gorman <mel@csn.ul.ie>
Subject: Re: [PATCH] add extra free kbytes tunable
References: <alpine.DEB.2.02.1302111734090.13090@dflat> <A5ED84D3BB3A384992CBB9C77DEDA4D414A98EBF@USINDEM103.corp.hds.com> <511EB5CB.2060602@redhat.com> <alpine.DEB.2.02.1302171546120.10836@dflat> <20130219152936.f079c971.akpm@linux-foundation.org> <alpine.DEB.2.02.1302192100100.23162@dflat> <20130222175634.GA4824@cmpxchg.org> <51307354.5000401@gmail.com> <51307583.2020006@gmail.com> <alpine.LNX.2.00.1303011431290.9961@eggly.anvils>
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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.