Discrepancy between sum of smaps rss and process rss

Discrepancy between sum of smaps rss and process rss

[Daniel Colascione]

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Hi linux-mm,

Do we expect the reporter process-wide RSS figure to differ from that of
the sum of the RSS fields of the individual VMAs as reported via smaps?
They're tracked very differently: the former is the sum
of MM_FILEPAGES, MM_ANONPAGES, and MM_SHMEMPAGES, while the latter comes
from counting pages in smaps_pte_entry (huge pages don't appear in this
context). The sum of the smaps rss fields is sometimes larger than the
counter-based values from status. Same with the anonymous sizes and the new
anonymous RSS in status.

Weirdly, I can't reproduce the discrepancy in a minimal UML boot with
init=/bin/sh (either with 4.4.88 or with latest master), but I can see this
discrepancy appear on both Android systems and normal Ubuntu 14.04 systems.

Before I spend more time debugging: is there something obvious that I
missed? Where should I be looking?

Thanks!

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