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Subject: Re: [RFC 2/3] mm: Add a new page flag PageLayzyFree() for MADV_FREE
To:     Wei Yang <richard.weiyang@gmail.com>,
        "Huang, Ying" <ying.huang@intel.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org,
        Dave Hansen <dave.hansen@linux.intel.com>,
        David Hildenbrand <david@redhat.com>,
        Mel Gorman <mgorman@suse.de>, Vlastimil Babka <vbabka@suse.cz>,
        Zi Yan <ziy@nvidia.com>, Michal Hocko <mhocko@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Minchan Kim <minchan@kernel.org>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Hugh Dickins <hughd@google.com>
References: <20200228033819.3857058-1-ying.huang@intel.com>
 <20200228033819.3857058-3-ying.huang@intel.com>
 <20200315081854.rcqlmfckeqrh7fbt@master>
From:   =?UTF-8?Q?Mika_Penttil=c3=a4?= <mika.penttila@nextfour.com>
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Date:   Sun, 15 Mar 2020 10:54:03 +0200
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On 15.3.2020 10.18, Wei Yang wrote:
> On Fri, Feb 28, 2020 at 11:38:18AM +0800, Huang, Ying wrote:
>> From: Huang Ying <ying.huang@intel.com>
>>
>> Now !PageSwapBacked() is used as the flag for the pages freed lazily
>> via MADV_FREE.  This isn't obvious enough.  So Dave suggested to add a
>> new page flag for that to improve the code readability.
> I am confused with the usage of PageSwapBacked().
>
> Previously I thought this flag means the page is swapin, set in
> swapin_readahead(). While I found page_add_new_anon_rmap() would set it too.
> This means every anon page would carry this flag. Then what is this flag
> means?
>
>

But not all PageSwapBacked() pages are anon, like shmem.


--Mika