Are they slim yet, round 2

A year later let’s see how Firefox fares on Windows, Linux, and OSX with multiple content processes enabled.


Graph comparing memory usage, chrome is still quite high

We can see that Firefox with four content processes fares better than Chrome on all platforms which is reassuring; Chrome is still about 2X worse on Windows and Linux. Our current plan is to only move up to four content processes, so this is great news.

Two content processes is still better than IE, with four we’re a bit worse. This is pretty impressive given last year we were in the same position with one content process.

Surprisingly on Mac Firefox is better than Safari with two content processes, compared with last year where we used 2X the memory with just one process, now we’re on par with four content processes.

I included Firefox with eight content processes to keep us honest. As you can see we actually do pretty well, but I don’t think it’s realistic to ship with that many nor do we currently plan to. We already have or are adding additional processes such as the plugin process for Flash and the GPU process. These need to be taken into consideration when choosing how many content processes to enable and pushing to eight doesn’t give us much breathing room. Making sure we have measurements now is important; it’s good to know where we can improve.

Overall I feel solid about these numbers, especially considering where we were just a year ago. This bodes well for the e10s-multi project.

Test setup

This is the same setup as last year. I load the first 30 pages of the tp5 page set (a snapshot of Alexa top 100 websites from a few years ago), each in its own tab, with 10 seconds in between loads and 60 seconds of settle time at the end.

Note: There was a minor change to the setup to give each page a unique domain. At least Safari and Chrome are roughly doing process per domain, so just using different ports on localhost was not enough. A simple solution was to modify my /etc/hosts file to add localhost-<1-30> aliases.


Measuring multiprocess browser memory usage is tricky. I’ve settled with a somewhat simple formula of:

total_memory = sum_uss(content processes) + sum_rss(parent processes); 

Where a parent process is defined as anything that is not a content process (I’ll explain in a moment). Historically there was just one parent process that manages all other processes, this is still somewhat the case but each browser still has other executables they may run in addition to content processes. A content process has a slightly different definition per browser, but is generally “where the pages are loaded” — this is an oversimplification, but it’s good enough for now.

My definitions:

Browser Content Definition Example “parent”
Firefox firefox processes launched with the -contentproc command line. firefox without the -contentproc command line, plugin-process which is used for Flash, etc.
Chrome chrome processes launched with the --type command line. chrome without out the --type command line, nacl_helper, etc.
Safari WebContent processes. Safari, SafariServices, SafariHistory, Webkit.Networking, etc.
IE iexplore.exe process launched with the /prefetch command line. iexplore without the /prefetch command line.
Edge MicrosoftEdgeCP.exe processes. MicrosoftEdge.exe, etc.

For Firefox this is a reasonable and fair measurement, for other browsers we might be under counting memory by a bit. For example Edge has a parent executable, MicrosoftEdge.exe, and a different content executable, MicrosoftEdgeCP.exe, arguably we should measure the RSS of one the MicrosoftEdgeCP.exe processes, and USS for the rest, so we’re probably under counting. On the other hand we might end up over counting if the parent and content processes are sharing dynamic libraries. In future measurements I may tweak how we sum the memory, but for now I’d rather possibly under count rather then worry about being unfair to other browsers.

Raw numbers

OS Browser Total Memory
Ubuntu 16.04 LTS Chrome 54 (see note) 1,478 MB
Ubuntu 16.04 LTS Firefox 55 – 2 CP 765 MB
Ubuntu 16.04 LTS Firefox 55 – 4 CP 817 MB
Ubuntu 16.04 LTS Firefox 55 – 8 CP 990 MB
macOS 10.12.3 Chrome 59 1,365 MB
macOS 10.12.3 Firefox 55 – 2 CP 1,113 MB
macOS 10.12.3 Firefox 55 – 4 CP 1,215 MB
macOS 10.12.3 Firefox 55 – 8 CP 1,399 MB
macOS 10.12.3 Safari 10.2 (see note) 1,203 MB
Windows 10 Chrome 59 1,382 MB
Windows 10 Edge (see note) N/A
Windows 10 Firefox 55 – 2 CP 587 MB
Windows 10 Firefox 55 – 4 CP 839 MB
Windows 10 Firefox 55 – 8 CP 905 MB
Windows 10 IE 11 660 MB

Browser Version Notes

  • Chrome 54 — aka chrome-unstable — was used on Ubuntu 16.04 LTS as that’s the latest branded version available (rather than Chromium)
  • Firefox Nightly 55 – 2 CP is Firefox with 2 content processes and one parent process, the default configuration for Nightly.
  • Firefox Nightly 55 – 4 CP is Firefox with 4 content processes and one parent process, this is a longer term goal.
  • Firefox Nightly 55 – 8 CP is Firefox with 8 content processes and one parent process, this is aspirational, a good sanity check.
  • Safari Technology Preview 10.2 release 25 was used on macOS as that’s the latest branded version available (rather than Webkit nightly)
  • Edge was disqualified because it seemed to bypass the hosts file and wouldn’t load pages from unique domains. I can do measurements so I might revisit this, but it wouldn’t have been a fair comparison as-is.

Are they slim yet?

In my previous post I focused on how Firefox compares against itself with multiple content processes. In this post I’d like to take a look at how Firefox compares to other browsers.

For this task I automated as much as I could, the code is available as the atsy project on github. My goal here is to allow others to repeat my work, point out flaws, push fixes, etc. I’d love for this to be a standardized test for comparing browsers on a fixed set of pages.

As with my previous measurements, I’m going with:

total_memory = RSS(parent) + sum(USS(children))

An aside on the state of WebDriver and my hacky workarounds

When various WebDriver implementations get fixed we can make a cleaner test available. I had a dream of automating the tests across browsers using the WebDriver framework, alas, trying to do anything with tabs and WebDriver across browsers and platforms is a fruitless endeavor. Chrome’s actually the only one I could get somewhat working with WebDriver.

Luckily Chrome and Firefox are completely automated. I had to do some trickery to get Chrome working, filed a bug, doesn’t sound like they’re interested in fixing it. I also had to do some trickery to get Firefox to work (I ended up using our marionette framework directly instead), there are some bugs, not much traction there either.

IE and Safari are semi-automated, in that I launch a browser for you, you click a button, and then hit enter when it’s done. Safari’s WebDriver extension is completely broken, nobody seems to care. IE’s WebDriver completely failed at tabs (among other things), I’m not sure where to a file a bug for that.

Edge is mostly manual, its WebDriver implementation doesn’t support what I need (yet), but it’s new so I’ll give it a pass. Also you can’t just launch the browser with a file path, so there’s that. Also note I was stuck running it in a VM from which was pretty old (they don’t have a newer one). I’d prefer not to do that, but I couldn’t upgrade my Windows 7 machine to 10 because Microsoft, Linux, bootloaders and sadness.

I didn’t test Opera, sorry. It uses blink so hopefully the Chrome coverage is good enough.

The big picture

Browser memory compared

The numbers

OS Browser Version RSS + USS
OSX 10.10.5 Chrome Canary 50.0.2627.0 1,354 MiB
OSX 10.10.5 Firefox Nightly (e10s) 46.0a1 20160122030244 1,065 MiB
OSX 10.10.5 Safari 9.0.3 (10601.4.4) 451 MiB
Ubuntu 14.04 Google Chrome Unstable 49.0.2618.8 dev (64-bit) 944 MiB
Ubuntu 14.04 Firefox Nightly (e10s) 46.0a1 20160122030244 (64-bit) 525 MiB
Windows 7 Chrome Canary 50.0.2631.0 canary (64-bit) 1,132 MiB
Windows 7 Firefox Nightly (e10s) 47.0a1 20160126030244 (64-bit) 512 MiB
Windows 7 IE 11.0.9600.18163 523 MiB
Windows 10 Edge 20.10240.16384.0 795 MiB

So yeah, Chrome’s using about 2X the memory of Firefox on Windows and Linux. Lets just read that again. That gives us a bit of breathing room.

It needs to be noted that Chrome is essentially doing 1 process per page in this test. In theory it’s configurable and I would have tried limiting its process count, but as far as I can tell they’ve let that feature decay and it no longer works. I should also note that Chrome has it’s own version of memshrink, Project TRIM, so memory usage is an area they’re actively working on.

Safari does creepily well. We could attribute this to close OS integration, but I would guess I’ve missed some processes. If you take it at face value, Safari is using 1/3 the memory of Chrome, 1/2 the memory of Firefox. Even if I’m miscounting, I’d guess they still outperform both browsers.

IE was actually on par with Firefox which I found impressive. Edge is using about 50% more memory than IE, but I wouldn’t read too much into that as I’m comparing running IE on Windows 7 to Edge on an outdated Windows 10 VM.