Description of problem: Consider the following case: # swapoff -a # free -m total used free shared buff/cache available Mem: 7686 1522 5244 312 918 5619 Swap: 0 0 0 # awk '/VmSwap/ && $2>0 {print}' /proc/*/status | sort -nr | head -n 5 VmSwap: 252 kB VmSwap: 128 kB VmSwap: 120 kB VmSwap: 100 kB VmSwap: 92 kB # VmSwap being > 0 is caused by mm counter caching and the values might be slightly off. A precise snapshot of a process memory use can be found in /proc/<pid>/smaps or /proc/<pid>/pagemap. pgmap(1), included in libpagemap, gets its data (USS/PSS/SWAP/RES/SHR) from /proc/<pid>/pagemap and should be accurate. It would be nice to have such uncached metrics available from PCP as well.
I don't know what are the requirement of pcp, but please note that getting the mm usage from smaps or pagemap is much more expensive than from status.
(In reply to Jerome Marchand from comment #1) > I don't know what are the requirement of pcp, but please note that getting > the mm usage from smaps or pagemap is much more expensive than from status. Good point - this can be seen already by running pgmap, it takes a few moments before getting any data. On the PCP side I'd expect these to be available somewhere under proc.psinfo so certainly not being logged by default. Thanks.
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There is nowadays a smaps_rollup file which is lighter weight to sample, if anyone has cycles to hack on this.
This was tackled awhile back... commit 21cdcaa07a64cc7f6b8aa9ae7b3ecbe60f4d2a78 Author: Nathan Scott <nathans> Date: Fri Mar 20 11:28:43 2020 +1100 pmdaproc: support proc.smaps.* metrics from /proc/pid/smaps_rollup Resolves https://github.com/performancecopilot/pcp/issues/569