Can we trust top/ps to really report what is going on.

Not usually; Linux allows memory overcommit. As I understand it (and simplifying somewhat), any application can request as much memory as is present on the machine (the VIRT column in top), but only the RES column is actually in use at any time. If all of the RES memory exceeds physical memory, it's swap time.

Without knowing what you watched grow and shrink in top, it's difficult to explain what happened.

In reply to Re: OS memory reclamation with threads on linux by chromatic
in thread OS memory reclamation with threads on linux by zentara

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