Re: [RESEND PATCH v3 2/3] docs: Add information about ipc sysctls limitations
From: Manfred Spraul <hidden>
Date: 2024-01-21 15:58:55
Hi Alexey, On 1/15/24 16:46, Alexey Gladkov wrote:
quoted hunk
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 <legion@kernel.org> Acked-by: "Eric W. Biederman" <redacted> Link: https://lkml.kernel.org/r/ede20ddf7be48b93e8084c3be2e920841ee1a641.1663756794.git.legion@kernel.org Signed-off-by: Eric W. Biederman <redacted> --- 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/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.
This block is about mqueue, not about SHM. Could you mention the change also in the change description. And: It is not fully clear to me what you mean with "respected hierarchically"
quoted hunk
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.
cgroups are an alternative to which part of the sentence? "prohibit the creation of a new ipc namespace"? or to the whole sentence? +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 + * use cgroups -- Manfred