Clean up some Mac memory code.

base/process/process_metrics.h

Index: base/process/process_metrics.h
diff --git a/base/process/process_metrics.h b/base/process/process_metrics.h
index 33cb64e24430f4bacf29d7a1ea8d3f873476f6d4..a68ef49113c9c2f4dbfe367986f5fce986b4e49e 100644
--- a/base/process/process_metrics.h
+++ b/base/process/process_metrics.h
@@ -63,8 +63,8 @@ struct IoCounters {
 // shareable:      0
 // swapped         Pages swapped out to zram.
 //
-// On OS X: TODO(thakis): Revise.
-// priv:           Memory.
+// On macOS:
+// priv:           Resident size (RSS) including shared memory.

[Alexei Svitkine (slow), 2017/03/29 20:12:26]

Note: based on what the GetCommittedAndWorkingSetKBytes() code.

[erikchen, 2017/03/29 20:25:14]

GetCommittedAndWorkingSetKBytes returns pmap->stats.resident_count
[see osfmk/i386/pmap.h and osfmk/kern/task.c].

This provides an underestimate of RSS [by any reasonable definition]. See
Appendix C under
https://docs.google.com/document/d/1zcfWSsgwTY8WYYlxd0G8QTR6_b2j38uMfjjXBOuMZ...,
look at section titled  "macOS: Use task_info(TASK_VM_INFO, …)".

I've intentionally avoided touching this comment because I want to overhaul this
entire file once my design doc has been fully reviewed.

[Alexei Svitkine (slow), 2017/03/29 21:02:39]

I see - should I just update the TODO to you and reference a crbug then?

Reason I wanted to provide more info is because in the meantime, this is being
used for Memory.Total2 and other metrics and having more info about what that's
counting rather than less is better in the meantime. I could expand my change
here and add a warning about it - similar (but shorter) to what you have in the
doc. WDYT?

[erikchen, 2017/03/29 21:10:38]

You're welcome to add a warning and a more accurate description.

[Alexei Svitkine (slow), 2017/03/29 21:16:54]

Done. PTAL.

 // shared:         0
 // shareable:      0
 //