On Tue, Apr 1, 2014 at 2:31 PM, Davidlohr Bueso <davidlohr@xxxxxx> wrote: > On Tue, 2014-04-01 at 14:10 -0400, KOSAKI Motohiro wrote: >> On Tue, Apr 1, 2014 at 1:01 PM, Davidlohr Bueso <davidlohr@xxxxxx> wrote: >> > On Mon, 2014-03-31 at 17:05 -0700, Andrew Morton wrote: >> >> On Mon, 31 Mar 2014 16:25:32 -0700 Davidlohr Bueso <davidlohr@xxxxxx> wrote: >> >> >> >> > On Mon, 2014-03-31 at 16:13 -0700, Andrew Morton wrote: >> >> > > On Mon, 31 Mar 2014 15:59:33 -0700 Davidlohr Bueso <davidlohr@xxxxxx> wrote: >> >> > > >> >> > > > > >> >> > > > > - Shouldn't there be a way to alter this namespace's shm_ctlmax? >> >> > > > >> >> > > > Unfortunately this would also add the complexity I previously mentioned. >> >> > > >> >> > > But if the current namespace's shm_ctlmax is too small, you're screwed. >> >> > > Have to shut down the namespace all the way back to init_ns and start >> >> > > again. >> >> > > >> >> > > > > - What happens if we just nuke the limit altogether and fall back to >> >> > > > > the next check, which presumably is the rlimit bounds? >> >> > > > >> >> > > > afaik we only have rlimit for msgqueues. But in any case, while I like >> >> > > > that simplicity, it's too late. Too many workloads (specially DBs) rely >> >> > > > heavily on shmmax. Removing it and relying on something else would thus >> >> > > > cause a lot of things to break. >> >> > > >> >> > > It would permit larger shm segments - how could that break things? It >> >> > > would make most or all of these issues go away? >> >> > > >> >> > >> >> > So sysadmins wouldn't be very happy, per man shmget(2): >> >> > >> >> > EINVAL A new segment was to be created and size < SHMMIN or size > >> >> > SHMMAX, or no new segment was to be created, a segment with given key >> >> > existed, but size is greater than the size of that segment. >> >> >> >> So their system will act as if they had set SHMMAX=enormous. What >> >> problems could that cause? >> > >> > So, just like any sysctl configurable, only privileged users can change >> > this value. If we remove this option, users can theoretically create >> > huge segments, thus ignoring any custom limit previously set. This is >> > what I fear. Think of it kind of like mlock's rlimit. And for that >> > matter, why does sysctl exist at all, the same would go for the rest of >> > the limits. >> >> Hmm. It's hard to agree. AFAIK 32MB is just borrowed from other Unix >> and it doesn't respect any Linux internals. > > Agreed, it's stupid, but it's what Linux chose to use since forever. > >> Look, non privileged user >> can user unlimited memory, at least on linux. So I don't find out any >> difference between regular anon and shmem. > > Fine, let's try it, if users complain we can revert. > >> >> So, I personally like 0 byte per default. > > If by this you mean 0 bytes == unlimited, then I agree. It's less harsh > then removing it entirely. So instead of removing the limit we can just > set it by default to 0, and in newseg() if shm_ctlmax == 0 then we don't > return EINVAL if the passed size is great (obviously), otherwise, if the > user _explicitly_ set it via sysctl then we respect that. Andrew, do you > agree with this? If so I'll send a patch. Yes, my 0 bytes mean unlimited. I totally agree we shouldn't remove the knob entirely. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>