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From: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
To: Christophe Leroy <christophe.leroy@csgroup.eu>,
 Rui Salvaterra <rsalvaterra@gmail.com>
Subject: Re: [Regression 5.7-rc1] Random hangs on 32-bit PowerPC (PowerBook6,
 7)
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Date: Wed, 20 May 2020 19:13:36 +0530
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Christophe Leroy <christophe.leroy@csgroup.eu> writes:

> Le 18/05/2020 =C3=A0 17:19, Rui Salvaterra a =C3=A9crit=C2=A0:
>> Hi again, Christophe,
>>=20
>> On Mon, 18 May 2020 at 15:03, Christophe Leroy
>> <christophe.leroy@csgroup.eu> wrote:
>>>
>>> Can you try reverting 697ece78f8f749aeea40f2711389901f0974017a ? It may
>>> have broken swap.
>>=20
>> Yeah, that was a good call. :) Linux 5.7-rc1 with the revert on top
>> survives the beating. I'll be happy to test a definitive patch!
>>=20
>
> Yeah I discovered recently that the way swap is implemented on powerpc=20
> expects RW and other important bits not be one of the 3 least=20
> significant bits (see __pte_to_swp_entry() )

The last 3 bits are there to track the _PAGE_PRESENT right? What is the
RW dependency there? Are you suggesting of read/write migration entry?
A swap entry should not retain the pte rw bits right?=20

A swap entry is built using swap type + offset. And it should not have a
dependency on pte RW bits. Along with type and offset we also should
have the ability to mark it as a pte entry and also set not present
bits. With that understanding what am I missing here?

>
> I guess the easiest for the time being is to revert the commit with a=20
> proper explanation of the issue, then one day we'll modify the way=20
> powerpc manages swap.
>

-aneesh