summaryrefslogtreecommitdiff
path: root/Documentation/admin-guide/sysctl
diff options
context:
space:
mode:
authorAlexey Gladkov <legion@kernel.org>2024-01-15 18:46:42 +0300
committerAndrew Morton <akpm@linux-foundation.org>2024-02-23 02:38:52 +0300
commit9220066ea807e3efce21476bffcac16743e9db22 (patch)
tree03b0331dad1db446d68ce32e15fb376411955999 /Documentation/admin-guide/sysctl
parent50ec499b9a43e46200c9f7b7d723ab2e4af540b3 (diff)
downloadlinux-9220066ea807e3efce21476bffcac16743e9db22.tar.xz
docs: add information about ipc sysctls limitations
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@kernel.org Signed-off-by: Alexey Gladkov <legion@kernel.org> Signed-off-by: Eric W. Biederman <ebiederm@xmission.com> Acked-by: "Eric W. Biederman" <ebiederm@xmission.com> Link: https://lkml.kernel.org/r/ede20ddf7be48b93e8084c3be2e920841ee1a641.1663756794.git.legion@kernel.org Cc: Christian Brauner <brauner@kernel.org> Cc: Davidlohr Bueso <dave@stgolabs.net> Cc: Joel Granados <joel.granados@gmail.com> Cc: Kees Cook <keescook@chromium.org> Cc: Luis Chamberlain <mcgrof@kernel.org> Cc: Manfred Spraul <manfred@colorfullife.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to 'Documentation/admin-guide/sysctl')
-rw-r--r--Documentation/admin-guide/sysctl/kernel.rst14
1 files changed, 11 insertions, 3 deletions
diff --git a/Documentation/admin-guide/sysctl/kernel.rst b/Documentation/admin-guide/sysctl/kernel.rst
index 6584a1f9bfe3..bc578663619d 100644
--- a/Documentation/admin-guide/sysctl/kernel.rst
+++ b/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
======