linux-kernel - Re: [RFC 2/3] mm: Add a new page flag PageLayzyFree() for MADV

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Message-ID: <20200315122217.45mioaxzuulwvx2f@master>
Date:   Sun, 15 Mar 2020 12:22:17 +0000
From:   Wei Yang <richard.weiyang@...il.com>
To:     Mika Penttil?? <mika.penttila@...tfour.com>
Cc:     Wei Yang <richard.weiyang@...il.com>,
        "Huang, Ying" <ying.huang@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        David Hildenbrand <david@...hat.com>,
        Mel Gorman <mgorman@...e.de>, Vlastimil Babka <vbabka@...e.cz>,
        Zi Yan <ziy@...dia.com>, Michal Hocko <mhocko@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Minchan Kim <minchan@...nel.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Hugh Dickins <hughd@...gle.com>
Subject: Re: [RFC 2/3] mm: Add a new page flag PageLayzyFree() for MADV_FREE

On Sun, Mar 15, 2020 at 10:54:03AM +0200, Mika Penttil?? wrote:
>
>
>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@...el.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.
>

Yes, while it looks shmem is the only exception.

I am still struggling to understand the meaning of this flag.

>
>--Mika

-- 
Wei Yang
Help you, Help me