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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Mon, 16 Mar 2020 09:21:34 +0800
From:   "Huang\, Ying" <ying.huang@...el.com>
To:     Wei Yang <richard.weiyang@...il.com>
Cc:     Mika Penttil?? <mika.penttila@...tfour.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

Wei Yang <richard.weiyang@...il.com> writes:

> 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.

Another exception is the pages freed lazily via MADV_FREE.

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

You can use `git blame` to find out the commit which introduces this
flag.  Which describes why this flag is introduced.

Best Regards,
Huang, Ying

>>
>>--Mika