From nobody Thu Apr 2 23:18:19 2026 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id B10B7C54EE9 for ; Tue, 20 Sep 2022 18:10:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230240AbiITSJ6 (ORCPT ); Tue, 20 Sep 2022 14:09:58 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42924 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231285AbiITSJo (ORCPT ); Tue, 20 Sep 2022 14:09:44 -0400 Received: from us-smtp-delivery-44.mimecast.com (us-smtp-delivery-44.mimecast.com [207.211.30.44]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7C04E60DA for ; Tue, 20 Sep 2022 11:09:35 -0700 (PDT) Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-185-DMmJYzxEOWSPHuBH53reNA-1; Tue, 20 Sep 2022 14:09:23 -0400 X-MC-Unique: DMmJYzxEOWSPHuBH53reNA-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.rdu2.redhat.com [10.11.54.6]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id D5E38802801; Tue, 20 Sep 2022 18:09:22 +0000 (UTC) Received: from comp-core-i7-2640m-0182e6.redhat.com (unknown [10.40.208.17]) by smtp.corp.redhat.com (Postfix) with ESMTP id EC0032166B26; Tue, 20 Sep 2022 18:09:20 +0000 (UTC) From: Alexey Gladkov To: LKML , Linux Containers , linux-doc@vger.kernel.org, linux-man@vger.kernel.org Cc: Andrew Morton , Christian Brauner , "Eric W . Biederman" , Kees Cook , Manfred Spraul , Jonathan Corbet Subject: [PATCH v2 3/3] docs: Add information about ipc sysctls limitations Date: Tue, 20 Sep 2022 20:08:22 +0200 Message-Id: In-Reply-To: References: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.1 on 10.11.54.6 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" After 25b21cb2f6d6 ("[PATCH] IPC namespace core") and 4e9823111bdc ("[PATCH] IPC namespace - shm") the shared memory page count stopped being global and started counting per ipc namespace. The documentation and shmget(2) still says that shmall is a global option. shmget(2): SHMALL System-wide limit on the total amount of shared memory, measured in units of the system page size. On Linux, this limit can be read and modified via /proc/sys/kernel/shmall. I think the changes made in 2006 should be documented. Signed-off-by: Alexey Gladkov Acked-by: "Eric W. Biederman" --- Documentation/admin-guide/sysctl/kernel.rst | 14 +++++++++++--- 1 file changed, 11 insertions(+), 3 deletions(-) diff --git a/Documentation/admin-guide/sysctl/kernel.rst b/Documentation/ad= min-guide/sysctl/kernel.rst index ee6572b1edad..c8b89bd8f004 100644 --- a/Documentation/admin-guide/sysctl/kernel.rst +++ b/Documentation/admin-guide/sysctl/kernel.rst @@ -541,6 +541,9 @@ default (``MSGMNB``). ``msgmni`` is the maximum number of IPC queues. 32000 by default (``MSGMNI``). =20 +All of these parameters are set per ipc namespace. The maximum number of b= ytes +in POSIX message queues is limited by ``RLIMIT_MSGQUEUE``. This limit is +respected hierarchically in the each user namespace. =20 msg_next_id, sem_next_id, and shm_next_id (System V IPC) =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D @@ -1181,15 +1184,20 @@ are doing anyway :) shmall =3D=3D=3D=3D=3D=3D =20 -This parameter sets the total amount of shared memory pages that -can be used system wide. Hence, ``shmall`` should always be at least -``ceil(shmmax/PAGE_SIZE)``. +This parameter sets the total amount of shared memory pages that can be us= ed +inside ipc namespace. The shared memory pages counting occurs for each ipc +namespace separately and is not inherited. Hence, ``shmall`` should always= be at +least ``ceil(shmmax/PAGE_SIZE)``. =20 If you are not sure what the default ``PAGE_SIZE`` is on your Linux system, you can run the following command:: =20 # getconf PAGE_SIZE =20 +To reduce or disable the ability to allocate shared memory, you must creat= e a +new ipc namespace, set this parameter to the required value and prohibit t= he +creation of a new ipc namespace in the current user namespace or cgroups c= an +be used. =20 shmmax =3D=3D=3D=3D=3D=3D --=20 2.33.4