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

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Date:   Fri, 1 Jun 2018 10:53:57 +0100
From:   Alex Richman <alex.r@...abs.co.uk>
To:     linux-man@...r.kernel.org, linux-mm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: mlock() confusing 1 half of system RAM limit

Hi,

I'm seeing a 1/2 of system RAM limit when calling mlock().  mlock(2) says:
 > ENOMEM (Linux 2.4 and earlier) the calling process tried to lock more 
than half of RAM.
Which implies to me that the 1 half of system RAM limit should be only 
Linux 2.4 and earlier, but I'm running linux 4.4.127 and still seeing 
the limit.

This is on a system with 66007168 KB total memory, locking 33794621440 
bytes works, locking 33795653632 bytes does not work.

Anyone know if this is the man pages or the kernel or something unrelated?

More details here: 
https://stackoverflow.com/questions/50639709/mlock-of-large-shm-address-range-fails-with-enomem-even-with-lots-of-free-memo

Thanks,
- Alex.

-- 
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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