linux-kernel - Re: [PATCH] Add a new test 'migrate.cow_after_fork' that verifies correct RMAP handling of Copy-On-Write pages after fork(). Before a write, parent and child share the same PFN; after a write, the child’s PFN differs, confirming proper COW duplication.

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Message-Id: <20251014142957.4253f2fc62e9e49bfc4433ab@linux-foundation.org>
Date: Tue, 14 Oct 2025 14:29:57 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: Itamar-Dalal <dalalitamar@...il.com>
Cc: linux-mm@...ck.org, linux-kselftest@...r.kernel.org,
 linux-kernel@...r.kernel.org, david@...hat.com, lorenzo.stoakes@...cle.com,
 riel@...riel.com, Liam.Howlett@...cle.com, vbabka@...e.cz,
 harry.yoo@...cle.com, jannh@...gle.com, rppt@...nel.org, surenb@...gle.com,
 mhocko@...e.com, shuah@...nel.org
Subject: Re: [PATCH] Add a new test 'migrate.cow_after_fork' that verifies
 correct RMAP handling of Copy-On-Write pages after fork(). Before a write,
 parent and child share the same PFN; after a write, the child’s PFN differs, confirming proper COW duplication.

On Tue, 14 Oct 2025 22:49:44 +0300 Itamar-Dalal <dalalitamar@...il.com> wrote:

> Subject: [PATCH] Add a new test 'migrate.cow_after_fork' that verifies correct RMAP handling of Copy-On-Write pages after fork(). Before a write, parent and child share the same PFN; after a write, the child’s PFN differs, confirming proper COW duplication.
> Date: Tue, 14 Oct 2025 22:49:44 +0300
> X-Mailer: git-send-email 2.34.1
> 
> Signed-off-by: Itamar-Dalal <dalalitamar@...il.com>
> ---
>  tools/testing/selftests/mm/rmap.c | 45 ++++++++++++++++++++++++++++++-
>  1 file changed, 44 insertions(+), 1 deletion(-)

OK, somehow your changelog was pasted into the email Subject, so please
resend.

Please prefix the Subject: with something which tells readers what part
of the kernel is affected. eg,

:
: Subject: selfstests/mm/rmap: verify correct RMAP handling of COW pages after fork()
:

Then enter the details in the changelog body, eg:

:
: Before a write, parent and child share the same PFN. After a write, the
: child’s PFN differs.  Check this to confirm proper COW duplication.
: