I'm uploading the Trace file here: https://www.dropbox.com/sh/wcxsdw94uqo793t/AABlNDgDx4W7S-tdnieBEb2na?dl=0

The browser did show an empty screen after I clicked 'stop' when the buffer was 100% full. I don't know if this one actually has anything real in it. 

I've left a second trace running but it also has been sat at 100% for a long time. Do I need to press stop? I'd expect as I requested a recording that fills the buffer to run till it is full then display the results.

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I have a similar issue, and I have an emergency fix that works -- if the system is sufficiently responsive to make it possible to apply.

Now using Chrome 51.0.2704.29 beta (64-bit) on  MacOS 10.11.3, but this issue has been more or less continuous over the last approximately six months so several versions of both are implicated.  Flash: completely removed.

About once a week following no clear pattern, my iMac suddenly becomes increasingly unresponsive over a short period, several minutes. Activity Monitor --> CPU Usage (which I routinely leave active) registers 100% for all processors.  If I can manage to open Activity Monitor --> Activity Monitor, I see  Memory Pressure has recently reached the top of the graph and is red.  I also observe multiple instances of GCH, many with memory allocations > 1GB.  (The record: 16GB.) 

Emergency measures:   By this point the system may be completely unresponsive, so the only choice is to shut down with the power button (or remote SSH) and re-boot.  

Sometimes I can still navigate within Activity monitor; if so, I look for the instance of GCH with the highest allocation (usually > 1GB) and force-quit that.  I continue knocking off GCH instances until Memory Pressure is re-established as moderate and green.  I don't touch GCH instances with normal (<< 1GB) allocations).  In every case, this restores normal system operation, open apps continue as before, and there's no clear ill effect on open Chrome pages. Crude, but effective.

HTH

[mac triage] I think this is normal. Google Chrome Helper processes include all memory used by a web page's javascript. Some badly written web pages may consume many GB of memory due to leaks before Chrome decides to kill them.

Please compare the PID column in Activity Monitor with the Chrome Task Manager, which you can access from Chrome Menu -> More Tools -> Task Manager.

Chrome will annotate each PID with the website(s) that are running in that helper process. If there's a mismatch, there may be a problem. Otherwise it's likely a particular website that consumes a lot of memory. Let us know if you see anything strange.

Comment #2 may be  Issue 373923 .

I keep forgetting to look at the CTM. Unfortunately it didn't totally help. 

Three processes have unusually high Memory usage. 
One is the Browser process itself
One is the tracing.. which incidentally shows as 3.3Gb in Activity Monitor.
The last looks to be a set of extensions and I think that was the one that I noticed first that sparked this thread. 

Is there anyway to get a better breakdown so I can tell which of the three extensions in that process might be the culprit?

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Thank you for providing more feedback. Adding requester "tapted@chromium.org" for another review and adding "Needs-Review" label for tracking.

For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot

What you see there are the extensions' background pages grouped together - extensions that have 'Content Scripts' may also reside in the memory used for the tabs.

But, that is quite a lot for the extensions' background pages. 100-200MB is more typical. I would try going to chrome://extensions and selectively unchecking the 'Enabled' checkbox to see if one of them is a big contributor.

@martin.a.ritchie: Could you please update the thread with the required information as per the comment #6

Thank you.

Hey guys, sorry for the delay in getting back to you. The machine crashed over the weekend so will have to wait for the memory usage to go crazy again. I'll look to narrow things down when it reoccurs but this time round the signs do point towards an  extension.

Thanks for your assistance, sorry I wasn't able to provide anything more concrete this time round. 

Thank you for providing more feedback. Adding "Needs-Review" label for tracking.

For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot

I'll leave this bug open for another week, so if you hit this case again, please let us know if any specific extension was the culprit (as per comment #6).

After about a week, we'll start getting nag mails from sheriffbot, so at that point it may be best to close out this bug and open a new one if the high memory usage crops up again.