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

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Date:   Fri, 1 Jun 2018 14:24:23 +0100
From:   Alex Richman <alex.r@...abs.co.uk>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     linux-man@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: mlock() confusing 1 half of system RAM limit

Ah, that's it.  Increased the limit on the mount and it works fine now.

Thanks!
- Alex.

On 01/06/18 14:05, Michal Hocko wrote:
> 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.

-- 
Alex Richman
alex.r@...abs.co.uk
Engineering
GB Labs
2 Orpheus House,
Calleva park,
Reading
RG7 8TA
Tel:+44 (0)118 455 5000
www.gblabs.com

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