Use isolate's cg-oom-killed to detect "memory limit exceeded" conditions - #1471
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gollux
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Jul 23, 2025
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I agree, but please wait with merging until the end of this IOI.
pxsit
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Jul 28, 2025
PHP has a memory_limit setting that limits the amount of memory the interpreter even tries to allocate; this limit is 128M by default. Exceeding this causes PHP to exit with code 255 (and print a message on stdout). This commit changes the limit to infinity, and lets isolate's memory limit handle it instead. This gives the correct feedback to contestants.
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Closes #912.
I deleted the extra text from killed-by-signal's help text because it's not relevant there anymore (I hope). I didn't re-add it to the new error's help text because in my experience, it's not true: in all cases I have tried, the oom killer has been precise enough that the reported memory use is exactly the task's memory limit (up to the rounding precision, at least). The behaviour that was described in that deleted paragraph might have been possible with non-cgroups isolate? I'm not sure.
Also, PHP has a
memory_limitsetting that limits the amount of memory the interpreter even tries to allocate; this limit is 128M by default. Exceeding this causes PHP to exit with code 255 (and print a message on stdout). This broke the new tests (and in fact, this could have been caught earlier: all the other oom tests were killed by signal, whereas php was nonzero exit code, but this fact was not checked by the test). Actually, this was a bigger problem, in that PHP enforced a 128MB memory limit, ignoring whatever the task's memory limit was. This would be possible to fix in php.ini on worker machines, but the contest administrators would have to be aware of it. I fixed it by changing the limit to -1 (meaning "infinite") using a command-line argument.