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c=relaxed/simple; d=linux-foundation.org; s=korg; t=1695342773; bh=A+v01Q6QfPOT5GvSCgfxalz/bjawMm8CUUKFpuPhXtQ=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=IL14HIDWESUt2Qml3tdEpv1jobiReIc/d141sl+CBb8zQTIbl7HHTNqjzPfdxee+f NF08oFI5iX6RcYrE9P7RJh82ZHqVEpaiVKB2SiriNUv8x7ouLx8JKf+10wErg7tc21 CFdltrsAfsxsSVFZ+OvmbaNl9WrAOcKCT3ORXwFY= Date: Thu, 21 Sep 2023 17:32:51 -0700 From: Andrew Morton To: Stefan Roesch Cc: kernel-team@fb.com, david@redhat.com, hannes@cmpxchg.org, riel@surriel.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH v3 0/2] mm/ksm: add fork-exec support for prctl Message-Id: <20230921173251.54b854fb0ec7af2bf3e3ec3b@linux-foundation.org> In-Reply-To: <20230921164709.3627565-1-shr@devkernel.io> References: <20230921164709.3627565-1-shr@devkernel.io> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 4AC1740002 X-Rspam-User: X-Rspamd-Server: rspam11 X-Stat-Signature: ph3yawikcyk1i7a4o9ykq4xkrwafzf7u X-HE-Tag: 1695342777-211937 X-HE-Meta: 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 958T5By0 B1H1bNl880opWsD5w7Ge72sQpzFowEfk5R/gJeP2EytHkT7zhdOnLOJ9Sp2hLh16Q0EbXJYBFR9Cg4an8bmmx/OJ1vvm/GKXQZ4azvrhqxeyn3s0H6w48PG0L91RR91L1PjdZf5DAQa29KPjqskqge59xDDh8LcaJ8bCVhyD+eHonuOArzknMn1NFt0zSQnk3ovQrq8pl54qXWAAlv33D87hdrHq3NkyOf/X8HOBYMIGezoDlqrSW9zIJVQJgYAaJpU8zR7upY+nrBBn7NTDDehi7pa+YiZcbgKHOZtMafruGNtUm+PtVZAKBqLOZJKG6YBILJso2E6GnWY8= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Thu, 21 Sep 2023 09:47:07 -0700 Stefan Roesch 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,