linux-kernel - Re: [PATCH] mips/mm: Add page soft dirty tracking

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Date:   Sun, 26 Apr 2020 19:09:26 +0200
From:   Paul Cercueil <paul@...pouillou.net>
To:     Thomas Bogendoerfer <tsbogend@...ha.franken.de>
Cc:     Guoyun Sun <sunguoyun@...ngson.cn>,
        Paul Burton <paulburton@...nel.org>,
        Daniel Silsby <dansilsby@...il.com>,
        Jiaxun Yang <jiaxun.yang@...goat.com>,
        Dmitry Korotin <dkorotin@...ecomp.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Steven Price <steven.price@....com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Anshuman Khandual <anshuman.khandual@....com>,
        linux-mips@...r.kernel.org, linux-kernel@...r.kernel.org,
        TieZhu Yang <yangtiezhu@...ngson.cn>,
        Xuefeng Li <lixuefeng@...ngson.cn>
Subject: Re: [PATCH] mips/mm: Add page soft dirty tracking

Hi Thomas,

Le dim. 26 avril 2020 à 18:54, Thomas Bogendoerfer 
<tsbogend@...ha.franken.de> a écrit :
> On Tue, Apr 21, 2020 at 05:15:27PM +0800, Guoyun Sun wrote:
>>  User space checkpoint and restart tool (CRIU) needs the page's 
>> change
>>  to be soft tracked. This allows to do a pre checkpoint and then dump
>>  only touched pages.
>> 
>>  Signed-off-by: Guoyun Sun <sunguoyun@...ngson.cn>
>>  ---
>>   arch/mips/Kconfig                    |  1 +
>>   arch/mips/include/asm/pgtable-bits.h |  8 ++++--
>>   arch/mips/include/asm/pgtable.h      | 48 
>> ++++++++++++++++++++++++++++++++++--
> 
> this breaks all 32bit builds where CPU support RIXI, because it 
> overflows
> pgtable_bits.

I think we'd need to make PTEs 64-bit at some point.

We wanted to add support for huge-pages on 32-bit MIPS and faced the 
same issue.

-Paul

> Thomas.
> 
> --
> Crap can work. Given enough thrust pigs will fly, but it's not 
> necessarily a
> good idea.                                                [ RFC1925, 
> 2.3 ]