The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/1c1ec069eb9f7b0ffc61e17e00d5ac2c5657cbc2

commit 1c1ec069eb9f7b0ffc61e17e00d5ac2c5657cbc2
Author: lgrey <lgrey@chromium.org>
Date: Mon Nov 07 16:33:44 2016

Per offline discussion, leaving "ChromeOS.MemoryPressureLevel" code in place for ChromeOS while history builds up in "Memory.PressureLevel"

BUG= 655304 

Review-Url: https://codereview.chromium.org/2434103003
Cr-Commit-Position: refs/heads/master@{#430292}

[modify] https://crrev.com/1c1ec069eb9f7b0ffc61e17e00d5ac2c5657cbc2/base/BUILD.gn
[modify] https://crrev.com/1c1ec069eb9f7b0ffc61e17e00d5ac2c5657cbc2/base/memory/memory_pressure_monitor.cc
[modify] https://crrev.com/1c1ec069eb9f7b0ffc61e17e00d5ac2c5657cbc2/base/memory/memory_pressure_monitor.h
[modify] https://crrev.com/1c1ec069eb9f7b0ffc61e17e00d5ac2c5657cbc2/base/memory/memory_pressure_monitor_chromeos.cc
[modify] https://crrev.com/1c1ec069eb9f7b0ffc61e17e00d5ac2c5657cbc2/base/memory/memory_pressure_monitor_chromeos.h
[modify] https://crrev.com/1c1ec069eb9f7b0ffc61e17e00d5ac2c5657cbc2/base/memory/memory_pressure_monitor_mac.cc
[modify] https://crrev.com/1c1ec069eb9f7b0ffc61e17e00d5ac2c5657cbc2/base/memory/memory_pressure_monitor_mac.h
[add] https://crrev.com/1c1ec069eb9f7b0ffc61e17e00d5ac2c5657cbc2/base/memory/memory_pressure_monitor_unittest.cc
[modify] https://crrev.com/1c1ec069eb9f7b0ffc61e17e00d5ac2c5657cbc2/base/memory/memory_pressure_monitor_win.cc

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/f518237b7651d1eeb115bffcc51f11ee0e9078cc

commit f518237b7651d1eeb115bffcc51f11ee0e9078cc
Author: lgrey <lgrey@chromium.org>
Date: Mon Nov 28 15:51:57 2016

[Mac] Report statistics more regularly in Mac memory pressure monitor

Currently, we only report UMA statistics on receiving a pressure
change event from the system. This means that we could be missing
many ticks of "normal" pressure from sessions that never encounter
pressure, skewing our stats. Other platforms don't have this issue
since they poll.

This change piggybacks statistic reporting on GetCurrentPressureLevel()
which is called regularly by RendererFrameManager::GetMaxNumberOfSavedFrames()
This also allows us to enable reporting for Sierra.

To make this work, GetCurrentPressureLevel is now declared non-const.
There don't appear to be any const MemoryPressureMonitors in the codebase
at the moment, so this should be safe.

BUG= 655304 

Review-Url: https://codereview.chromium.org/2495003004
Cr-Commit-Position: refs/heads/master@{#434660}

[modify] https://crrev.com/f518237b7651d1eeb115bffcc51f11ee0e9078cc/base/memory/memory_pressure_monitor.h
[modify] https://crrev.com/f518237b7651d1eeb115bffcc51f11ee0e9078cc/base/memory/memory_pressure_monitor_chromeos.cc
[modify] https://crrev.com/f518237b7651d1eeb115bffcc51f11ee0e9078cc/base/memory/memory_pressure_monitor_chromeos.h
[modify] https://crrev.com/f518237b7651d1eeb115bffcc51f11ee0e9078cc/base/memory/memory_pressure_monitor_mac.cc
[modify] https://crrev.com/f518237b7651d1eeb115bffcc51f11ee0e9078cc/base/memory/memory_pressure_monitor_mac.h
[modify] https://crrev.com/f518237b7651d1eeb115bffcc51f11ee0e9078cc/base/memory/memory_pressure_monitor_win.cc
[modify] https://crrev.com/f518237b7651d1eeb115bffcc51f11ee0e9078cc/base/memory/memory_pressure_monitor_win.h
[modify] https://crrev.com/f518237b7651d1eeb115bffcc51f11ee0e9078cc/chrome/browser/chromeos/resource_reporter/resource_reporter_unittest.cc
[modify] https://crrev.com/f518237b7651d1eeb115bffcc51f11ee0e9078cc/chromecast/browser/cast_memory_pressure_monitor.cc
[modify] https://crrev.com/f518237b7651d1eeb115bffcc51f11ee0e9078cc/chromecast/browser/cast_memory_pressure_monitor.h

Looks like we're getting data for canary. Comparing vs. Windows canary, it percentage of time spent in moderate/critical pressure is lower, but I'm not sure if that's a difference between what platforms consider critical, more low-end Windows machines, programmer error or one of another million reasons. Marking fixed for now nonetheless.

I was looking at this data last night - great to have it!

It appears that on Windows, the memory pressure levels are based on free memory being within certain ranges whereas on the Mac it's based on if the system is compressing pages in RAM (WARNING) or swapping to disk (CRITICAL). As I see it the different platform memory pressures are therefore not comparable because on Windows, WARNING means you have less free memory available but on the Mac there might be ample free memory that can be reclaimed through compression.