Re: [PATCH v3 0/2] mm/ksm: add fork-exec support for prctl

[Andrew Morton]

On Thu, 21 Sep 2023 09:47:07 -0700 Stefan Roesch <shr@xxxxxxxxxxxx> wrote:

> A process can enable KSM with the prctl system call. When the process is
> forked the KSM flag is inherited by the child process.

I guess that's logical, as it's still the same program.

> However if the
> process is executing an exec system call directly after the fork, the
> KSM setting is cleared. This patch series addresses this problem.

Well...  who said it's a problem?  There's nothing in our documentation
about this(?).  Why is the current behavior wrong?  If the new program
wants KSM, it can turn on KSM.

This significant change in user-visible behavior deserves much more
explanation and justification, please.  Including an explanation of why
it's OK to change kernel behavior under existing users' feet like this,