Any read or write (by root only) flushes all the per-cpu vm statistics into their global totals, for more accurate reports when testing e.g. cat /proc/sys/vm/stat_refresh /proc/meminfo
As a side-effect, it also checks for negative totals (elsewhere reported as 0) and “fails” with EINVAL if any are found, with a warning in dmesg. (At time of writing, a few stats are known sometimes to be found negative, with no ill effects: errors and warnings on these stats are suppressed.)
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