The patch titled
Subject: docs: add information about ipc sysctls limitations
has been added to the -mm mm-nonmm-unstable branch. Its filename is
docs-add-information-about-ipc-sysctls-limitations.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/docs-add-information-about-ipc-sysctls-limitations.patch
This patch will later appear in the mm-nonmm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Alexey Gladkov <legion@xxxxxxxxxx>
Subject: docs: add information about ipc sysctls limitations
Date: Mon, 15 Jan 2024 15:46:42 +0000
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.
Link: https://lkml.kernel.org/r/09e99911071766958af488beb4e8a728a4f12135.1705333426.git.legion@xxxxxxxxxx
Signed-off-by: Alexey Gladkov <legion@xxxxxxxxxx>
Signed-off-by: Eric W. Biederman <ebiederm@xxxxxxxxxxxx>
Acked-by: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
Link: https://lkml.kernel.org/r/ede20ddf7be48b93e8084c3be2e920841ee1a641.1663756794.git.legion@xxxxxxxxxx
Cc: Christian Brauner <brauner@xxxxxxxxxx>
Cc: Davidlohr Bueso <dave@xxxxxxxxxxxx>
Cc: Joel Granados <joel.granados@xxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Luis Chamberlain <mcgrof@xxxxxxxxxx>
Cc: Manfred Spraul <manfred@xxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
Documentation/admin-guide/sysctl/kernel.rst | 14 +++++++++++---
1 file changed, 11 insertions(+), 3 deletions(-)
--- a/Documentation/admin-guide/sysctl/kernel.rst~docs-add-information-about-ipc-sysctls-limitations
+++ a/Documentation/admin-guide/sysctl/kernel.rst
@@ -594,6 +594,9 @@ default (``MSGMNB``).
``msgmni`` is the maximum number of IPC queues. 32000 by default
(``MSGMNI``).
+All of these parameters are set per ipc namespace. The maximum number of bytes
+in POSIX message queues is limited by ``RLIMIT_MSGQUEUE``. This limit is
+respected hierarchically in the each user namespace.
msg_next_id, sem_next_id, and shm_next_id (System V IPC)
========================================================
@@ -1274,15 +1277,20 @@ are doing anyway :)
shmall
======
-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 used
+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)``.
If you are not sure what the default ``PAGE_SIZE`` is on your Linux
system, you can run the following command::
# getconf PAGE_SIZE
+To reduce or disable the ability to allocate shared memory, you must create a
+new ipc namespace, set this parameter to the required value and prohibit the
+creation of a new ipc namespace in the current user namespace or cgroups can
+be used.
shmmax
======
_
Patches currently in -mm which might be from legion@xxxxxxxxxx are
sysctl-allow-change-system-v-ipc-sysctls-inside-ipc-namespace.patch
docs-add-information-about-ipc-sysctls-limitations.patch
sysctl-allow-to-change-limits-for-posix-messages-queues.patch
