Re: mlock() confusing 1 half of system RAM limit

[Michal Hocko]

On Fri 01-06-18 13:26:59, Alex Richman wrote:
> I am using a shm MAP_SHARED, along these lines:
> > shm_fd = shm_open(handle, (O_RDWR | O_CREAT), (S_IRWXU | S_IRWXG |
> S_IRWXO));
> > ftruncate(shm_fd, channel->sled_size)
> > channel->sled = mmap(NULL, channel->sled_size, (PROT_READ | PROT_WRITE),
> > (MAP_SHARED | MAP_NORESERVE), shm_fd, 0);
> > mlock(channel->sled, channel->sled_size) /* Fails with ENOMEM. */
> 
> But shmmax is unlimited on my box:
> # sysctl -a | grep shm
> kernel.shm_next_id = -1
> kernel.shm_rmid_forced = 0
> kernel.shmall = 18446744073692774399
> kernel.shmmax = 18446744073692774399
> kernel.shmmni = 4096
> 
> Any ideas?

shm_open uses tmpfs/shmem under the cover and that has the internal
limit as explained above.
-- 
Michal Hocko
SUSE Labs