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

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Date:   Sun, 15 Mar 2020 10:54:03 +0200
From:   Mika Penttilä <mika.penttila@...tfour.com>
To:     Wei Yang <richard.weiyang@...il.com>,
        "Huang, Ying" <ying.huang@...el.com>
Cc:     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 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.


--Mika