Adjust "vm_memory_high_watermark" code to be more forgiving/strict about bad data (such as a memory limit of zero)

[tianon]

See also #148 and #147.

[tianon]

Ok, this is confirmed to be FALSE; time to keep digging (although this PR's changes are probably still sane, possibly minus the 0 special-casing):

$ docker info > /dev/null
WARNING: No memory limit support
WARNING: No swap limit support
WARNING: No kernel memory limit support
WARNING: No oom kill disable support
WARNING: No cpu cfs quota support
WARNING: No cpu cfs period support
$ docker run --rm bash ls -l /sys/fs/cgroup/memory
ls: /sys/fs/cgroup/memory: No such file or directory

[AnatolyRugalev]

@tianon could you please information about this var to README please? I just spend an hour trying to figure out what is wrong with my container

UPD: ah, sorry. Didn't know that docs are in another repo

[tianon]

Docs PR is up at docker-library/docs#879. 👍

[tianon]

Yesss, thanks to @jamesmallen, I've managed to hack something together to reproduce the issue:

$ echo 18446744073709551615 > lol-limit
$ docker run -it --rm -v "$PWD/lol-limit":/sys/fs/cgroup/memory/memory.limit_in_bytes rabbitmq:alpine
...

=INFO REPORT==== 11-Apr-2017::20:23:20 ===
Memory limit set to 0MB of 32148MB total.

...

[tianon]

PR is updated! I've tested that several values calculate correctly now (uses awk for all math processing, since we can't know what the scale of these numbers will be, but know that they need to handle at least 64bit unsigned integers).

[tianon]

By bind-mounting an empty file over /proc/meminfo (with my lol-limit from above to get 18446744073709551615), I got { vm_memory_high_watermark, { absolute, 7378697629483821056 } } (which is 40% of 18446744073709551615 👍).

I mean, RabbitMQ then gets (rightfully) grumpy, but it's a valid test of our code at least. 👍

=WARNING REPORT==== 11-Apr-2017::20:36:59 ===
Unknown total memory size for your OS {unix,linux}. Assuming memory size is 1024MB.

=INFO REPORT==== 11-Apr-2017::20:36:59 ===
Memory limit set to 1024MB of 1024MB total.

[tianon]

(And by bad things, I mean throws some scary output, and then starts successfully, like a true trooper. 🤘)

[AnatolyRugalev]

@tianon wow this is a huge numbers. Great work!