Messages in this thread | | | Date | Sun, 04 May 2014 12:29:08 +0300 | From | Marian Marinov <> | Subject | Re: [PATCH] IPC initialize shmmax and shmall from the current value not the default |
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On 05/04/2014 04:20 AM, Davidlohr Bueso wrote: > On Sun, 2014-05-04 at 03:28 +0300, Marian Marinov wrote: >> On 05/04/2014 02:53 AM, Davidlohr Bueso wrote: >>> On Sun, 2014-05-04 at 01:48 +0300, Marian Marinov wrote: >>>> When we are creating new IPC namespace that should be cloned from the current namespace it is a good idea to copy the >>>> values of the current shmmax and shmall to the new namespace. >>> >>> Why is this a good idea? >>> >>> This would break userspace that relies on the current behavior. >>> Furthermore we've recently changed the default value of both these >>> limits to be as large as you can get, thus deprecating them. I don't >>> like the idea of this being replaced by namespaces. >>> >>> Thanks, >>> Davidlohr >>> >> >> The current behavior is create_ipc_ns()->shm_init_ns() >> >> void shm_init_ns(struct ipc_namespace *ns) >> { >> ns->shm_ctlmax = SHMMAX; >> ns->shm_ctlall = SHMALL; >> ns->shm_ctlmni = SHMMNI; >> ns->shm_rmid_forced = 0; >> ns->shm_tot = 0; >> ipc_init_ids(&shm_ids(ns)); >> } >> >> This means that whenever you are creating an IPC namespace it gets its SHMMAX and SHMALL values from the defaults for >> the kernel. > > This is exactly what I meant by 'current behavior'. > >> If for some reason you want to have smaller(or bigger, for older kernels) limit. This means changing the values in >> /proc/sys/kernel/shmmax and /proc/sys/kernel/shmall. However the program that is started with the new IPC namespace may >> lack privileges to write to these files and so it can not modify them. > > I see no reason why namespaces should behave any different than the rest > of the system, wrt this. And this changes how *and* when these limits > are set, which impacts at a userspace level with no justification. > >> What I'm proposing is simply to copy the current values of the host machine, as set by a privileged process before the >> namespace creation. >> >> Maybe a better approach would be to allow the changes to be done by processes having CAP_SYS_RESOURCE inside the new >> namespace? > > Why do you need this? Is there any real impact/issue you're seeing? > I'm using Linux Containers and I need to be able to either start containers with different SHMMAX or set different SHMMAX to already running containers without giving them full root access.
-Marian
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