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>multiplied by the number of processes

Why aren't the pages shared like other dynamic libraries?

If we put the PID into the vDSO, this data page can no longer be shared among different processes (at least not in the same container).

We could use the rseq area for PID and TID.

Because you just asked to put data there that would differ per process?

That doesn't mean that code pages couldn't be shared. The data that differs per process is a single number in this case.

Having said that I agree that it's probably not worth it to put getpid() into vDSO.

A number here, a number there, before you know it, it is a lot.

If we're going to add all sorts of dross to the vdso, like getpid(), who knows what else will end up there?