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Subject: Re: [RFC PATCH v2 9/9] mm: Introduce Copy-On-Write PTE table
Thread-Topic: [RFC PATCH v2 9/9] mm: Introduce Copy-On-Write PTE table
Thread-Index: AQHY0o4wEIMbrk5BdEK3BIHQI3SfK63zm3IAgAAVHoCAATBzgIABi4GAgAA/C4CAABIqAIAAAxgA
Date:   Thu, 29 Sep 2022 18:40:36 +0000
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On Sep 29, 2022, at 11:29 AM, Chih-En Lin <shiyn.lin@gmail.com> wrote:

> That case could be caught in copy_pte_range(): in case we'd have to alloc=
ate
>> a page via page_copy_prealloc(), we'd have to fall back to the ordinary
>> "separate page table for the child" way of doing things.
>>=20
>> But that looks doable to me.
>=20
> Sounds good. :)

Chih-En, I admit I did not fully read the entire correspondence and got dee=
p
into all the details.

I would note, however, that there are several additional components that I
did not see (and perhaps missed) in your patches. Basically, there are many
page-table manipulations that are done not through the page-fault handler o=
r
reclamation mechanisms. I did not see any of them being addressed.

So if/when you send a new version, please have a look at mprotect(),
madvise(), soft-dirty, userfaultfd and THP. In these cases, I presume, you
would have to COW-break (aka COW-unshare) the page-tables.