Category: Memory consumption

IMAGES

The big news this week is that Timothy Nikkel finished bug 689623, which causes us to (for the most part) only decode images that are visible or nearly visible.  This goes a long way towards fixing our problems with decoded images which happens to be the #1 item on the MemShrink big ticket items list.  The fixing of this bug also happened to fix the following bugs in passing:  661304, 682230.

To give you an idea of what changed, consider an image-heavy page like this one.  Prior to Timothy’s change, shortly after loading that page on my machine Firefox’s memory consumption would reach 3 GiB, with 2.7 GiB of that being decoded (uncompressed) images.  If I switched to another tab then 2.45 GiB of those decoded images would be immediately discarded, then after 10–20 seconds the remaining 250 MiB would be.  If I switched back, all the images would immediately be decoded again and memory consumption would climb back to 3 GiB.

After Timothy’s change, Firefox’s memory consumption still peaks around 2.8 GiB just after loading the page, but then quickly drops back to 600 MiB as many of those decoded images are discarded.  After that, even when scrolling quickly through the page I couldn’t get memory consumption to exceed 700 MiB.

This change will make such pages much smoother on desktop machines that don’t have lots of RAM, because there won’t be any paging, which slows things down drastically.   Andrew McCreight wrote a comment that I can’t find now, but basically he said that on one of his machines, that page was extremely slow and painful to scroll through before the change, and after the change it was smooth and pleasant.

The peak that occurs when an image-heavy page first loads is still undesirable, and bug 542158 is open for fixing that, and it will build on the infrastructure that Timothy has developed.  When that’s fixed, it’ll also greatly reduce the likelihood that an image-heavy page will cause an out-of-memory (OOM) crash, which is great for both desktop (esp. 32-bit Windows) and mobile/B2G.

Miscellaneous

Nicolas Pierron fixed a leak in IonMonkey that was causing runaway memory consumption for Shumway demos on Android.  It has been backported to the Aurora and Beta channels.

I greatly reduced the size of the property cache.  This is a data structure the JS engine uses to speed up property accesses.  It used to be important, but is now barely necessary thanks to type inference and the JITs.  This reduced memory consumption by 75 KiB per JSRuntime on 32-bit, and by 150 KiB per JSRuntime on 64-bit.  There is one JSRuntime for each process, plus one for each worker, so for B2G it saves around 525 KiB at start-up.

We declared victory in the bug tracking the memory consumption of not-yet-loaded tabs.  When the bug was opened it was over 1 MiB per tab (64-bit builds), it’s now around 200 KiB.  Furthermore, if someone has many (e.g. hundreds) of not-yet-restored tabs they’re probably on a high-end machine, so the motivation for further reducing the memory consumption is low.  There is a bug open about some scripts run for each of these tabs, however;  avoiding these scripts may make start-up faster for heavy tab users.

Marco Bonardo reduced the maximum size of the cache used by each SQLite connection (excluding places.sqlite) from 4 MiB to 2 MiB.  Update: Marco corrected me in the comments — there are four places.sqlite connections, but only one of them (the one for the awesome bar) is excluded from the new 2 MiB limit.

Somebody fixed a leak in the Roboform add-on.  The fix is present in v7.8.7.5.

Olli Pettay improved our memory reporting by adding extra information to some system compartments that previously were undistinguished.  Our experience has been that as soon as somebody adds a new memory measurement, it finds a problem, and this was no exception, leading to the filing of bug 844661 .

Jonathan Kew has been busy.

• He reverted a 22 MiB regression on AWSY/mobile.
• He reduced Fennec’s start-up memory consumption by about 2 MiB by doing clever things with fonts.
• He made it so that hyphenation dictionaries (which can be several MiBs in size) are discarded on memory pressure events.

I wrote a script that can take a diff of two JSON memory report dumps.  This will be very useful when comparing the memory consumption before and after doing something, for example.  If you didn’t know that JSON memory report dumps existed, you’re probably not alone — it’s an undocumented feature that’s currently only available on Linux and Android, and is triggered by sending signal 34 to the browser(!)  These dumps can be loaded by about:memory (see the buttons at the bottom) but there’s currently no easy way to trigger them, which is why today I filed a bug to make it easier.

I removed the pool used for recycling nsNodeInfo objects, which was causing them to never be released back to the OS.  Never-shrinking structures like this can become a problem in longer-running browser sessions — for example, after running MemBench, which opens and closes 150 tabs, this pool was unnecessarily hoarding 4 MiB.

INteresting Open Bugs

In my MemShrink reports I mostly write about bugs that have been fixed.  While this is satisfying and demonstrates progress, it might also give the impression that the MemShrink team has everything under control, when really we could use some help.

(In fact, the term “the MemShrink team” is something of a misnomer since there isn’t any such entity, officially.  “The people who regularly attend MemShrink meetings” would be a more accurate term.  But I’ll use “MemShrink team” as a short-hand for that.)

The MemShrink team has expertise in some areas of Mozilla code, such as DOM, cycle collector, JS engine (partial), Fennec, B2G, and memory profiling, and we tend to make good progress in those areas — we can fix bugs in those areas, and we generally pay attention to how these areas affect memory consumption.

But we lack expertise in areas like graphics, image-handling, layout, text rendering, storage, Jetpack/add-ons, and front-end.  Graphics is a particular problem, because graphics issues, esp. those involving drivers, can cause huge memory consumption blow-ups.  Bug 837542 is an example from the MemShrink:P1 list where gradients are somehow causing memory consumption to spike by 10s or even 100s of MiBs just by opening and closing a few tabs!  We triage bugs like that as well as we can, but often we’re just guessing, and we’re mostly helpless to address such problems.

Therefore, moving forwards I’m going to start mentioning interesting open bugs that don’t have someone working on them.

One example is bug 846173, which I filed when I noticed that fully loading the front page of TechCrunch takes over 100 MiB!  And it’s mostly because of the many Facebook “like” buttons, Google “+1” buttons, and Twitter “tweet this” buttons — see the about:memory output for the full gory details.  It’s obvious that most of these window objects are basically identical, except for the URL.  Could we do something clever to avoid all this duplication?  Justin Lebar wondered about a copy-on-write scheme.  Are there other ways we could improve this case?

Another example is bug 842003, which is looking for an owner.  Some basic leak-checking infrastructure in the IPC code could potentially detect some big problems for B2G.

In bug 842979 we’re seeing 10s or 100s of MiBs of orphan DOM nodes in long-running Gmail sessions.  It’s not clear if this is a bug in Gmail, or caused by add-ons, or something else.  Please comment in the bug if you have any additional data.

Another one:  DMD, which is one of our most important tools, is pretty much useless on Fennec because it can’t get stack traces.  If anyone who knows about such things would like to investigate, that would be very helpful.  (In fact, I got a crash in the stack tracing code when I most recently tried to run DMD on Mac, which I haven’t had time to investigate.)

Bug Counts

Here are the current bug counts.

• P1: 12 (-6/+1)
• P2: 128 (-7/+7)
• P3: 122 (-0/+5)
• Unprioritized: 6 (-2/+6)

The closed P1s were 661304, 689623, 837187, 841976, 841993, 842756.  Three of them related to an IPC leak fix that I mentioned in my last report.

I recently wrote about the wonderful “Reset Firefox” feature, which in one fell swoop can fix all sorts of bad behaviours.  What follows is a number of complaints that commenters had, and some ideas about how to address them.

“The name is misleading”

It’s true.  It sounds like it will erase all of your data and customizations.  The SUMO page says the following.

The Reset Firefox feature can fix many issues by restoring Firefox to its factory default state while saving your essential information.

“Factory default state” and “while saving your essential information” are two phrases that sit together awkwardly. But it may be too late to change the name now.

“But I have lots of configuration tweaks”

And they’ll all be lost.  You can look in about:support to see “important modified preferences”.  Or you can look at the “user set” entries in about:config.  Or you can look at both, and wonder the two lists are different, and what the definition of “important” is.

It would be very helpful if you could see who or what was responsible for each of those changes.  Was it the user, via the Preferences dialog?  The user via about:config?  An add-on?  Something auto-updated by core Firefox code?  (And why do I always have dozens of “user set” preferences relating to printing, even on my Linux machine that I never print from?)

Would an API tweak help?  We could change the “setPref()” function (or whatever it’s called) to take an additional, optional argument that indicates who set it.  It wouldn’t fix the problem immediately but would give a path forward.

Update: I found bug 834034, which is about preserving a user’s custom spell-check dictionary.

“But I have hundreds of tabs open”

And they’ll all be lost, too.  Apparently the Session Manager extension solves this problem.  But that’s not obvious, and still a pain to manage.  Maybe we could mention it in the documentation?

Update: Alexander Limi pointed me in the direction of bug 833943, which is about fixing this.

“But I have Dozens of add-ons installed”

And one of them might be causing your problems.  You can get the list of installed add-ons from about:addons, so this one isn’t too hard to fix up manually.

“I can’t see the ‘Reset Firefox’ button” / “I want to reset a non-default profile”

The “Reset Firefox” button only shows up in the default profile.  (And sometimes not even there — I don’t get it on my default profile on my dev machine, where I have half a dozen profiles present.)

There’s a bug open about this.  I could be wrong, but it doesn’t sound that hard to fix.

“How do I undo it if it breaks something?”

The SUMO page addresses this.

After the reset is finished, your old Firefox profile information will be placed on your desktop in a folder named “Old Firefox Data.” If the reset didn’t fix your problem you can restore some of the information not saved by copying files to the new profile that was created. See Copying files between profile folders for instructions.

The instructions on copying files between profile folders are clear, except for the fact that even an expert user will have little idea which files within a profile are important.  It’s an intimidating process.

“Why isn’t this automated?”

Well, because it loses some of your configuration.  You don’t want Firefox discarding all your extensions every six months.

“Why is this even needed in the first place?”

Ah.  An interesting question.  What exactly are the sources of the problems that Reset Firefox fixes?

• Problematic extensions.  This is probably a common cause of problems, especially for people who have toolbars they don’t want and things like that.  And I’ll give a special mention to GreaseMonkey users who have badly written scripts that do horrible things.
• Bad preference settings.  In my experience, the most likely settings to cause problems are those involving hardware acceleration (e.g. bug 711656). Are there any other classes of preferences that could have big effects?  I guess if the JavaScript JITs were turned off that would slow things down drastically.  I don’t know how people end up with a bad setting, whether it’s by diffling in about:config or extensions or something else.  (The was a dev-platform thread about this last year.)
• Corrupt(?) state.  This one’s vague, but I suspect it’s a factor.  Maybe some of the SQLite files?  Or perhaps the state isn’t corrupt, but just fragmented in some fashion?  For example, in an oldish profile on my Mac my places.sqlite file size is 73 MiB, and urlclassifier3.sqlite is 42 MiB, which seems like a lot.
• Do we know of any other causes?

Update: in bug 754933 Michael Verdi lists the following preferences as “troublesome”:

• home page
• all search engines (location bar, search bar, right-click)
• Application settings
• History settings
• Password settings
• Proxy settings
• Firefox update settings
• SSL settings
• All toolbars and controls

I don’t subscribe to the hardline “Reset Firefox shouldn’t even be necessary” viewpoint — software is hard.  But I would like to understand the root causes better, in order to understand if at least some of them could be reduced or prevented.

It’s not all bad

I hope this post doesn’t sound too negative.  I understand that Reset Firefox’s goal was to provide something really simple that’ll fix many problems, and it does that admirably.

It’s just a shame that some power users who genuinely want to improve Firefox’s behaviour are unable to try it because it discards too much data.  I wonder if having additional options (in an obscure corner of the UI) the way safe mode does — “preserve extensions”, “preserve preferences”, “preserve open tabs” — would help those users.  Then those users could use a more incremental approach:  discard some data away, see if that helps, discard some more, etc.

Or maybe that’s not worthwhile;  the people who comment on my blog aren’t exactly typical Firefox users!  And it could complicate things for the SUMO folks — they’d have to ask what options someone used when they initiated a Reset Firefox.  I’m not sure.  I’d just love to extend the goodness of Reset Firefox as far and wide as possible, and it seems like a few small tweaks might help.

TL;DR: Please recommend the “Reset Firefox” feature to anyone who complains about odd, persistent performance problems and/or high memory consumption.

In Ars Technica’s article about the Firefox 19 release, carbon fibre made a comment complaining about Firefox’s performance.

Firefox still doesn’t fix memory issues and smoothness, at least on my experience. It’s constant random jerks and extreme mem usage, until restarted. I use chrome but I have been wanting to switch FF for awhile, but I can’t, as long as they fix these issues, long standing issues since ver. 4.

There were four notable responses.

korg250 (my emphasis):

They are losing market share by not fixing the memory issues. Even on my 8GB SSD i5 system I have to restart it when it reaches over 1 GB because it starts to slow down A LOT. And it get over 1 GB very fast for someone who constantly open/close tabs like me (even in safe mode).

I was an avid FF user until I saw myself installing an add-on to restart FF when it reaches X MB of memory usage. Today I use Opera for most of my browsing but I some sites does not work properly with Opera and some extensions only exist on FF.

Shame.

abhi_beckert:

Do you have extensions installed? Maybe one of them is causing it.

crislevin:

every benchmark I saw, firefox uses less memory than everybody else, I really don’t get why people complain about it?

nnethercote:

You might have problems with your profile. Visit about:support, and click on the “Reset Firefox” button in the top right corner. It’ll generated a new profile that preserves much of your browsing history, though it will disable any add-ons you have. (It’ll give you details about exactly what it preserves and discards before doing so, so you can cancel it if you change your mind.) This step fixes a lot of performance problems like the ones you describe.

To summarize the responses:

• Me too!  It sucks.
• Are extensions to blame?  (A reasonable question, though less likely since Firefox 15 fixed most extension-related leaks, and one that can be difficult to answer conclusively.)
• Really?
• Is a busted profile to blame?  Try “Reset Firefox” to determine if so.

carbon fibre didn’t respond, but korg250 (the “Me too!” commenter) took up the commenting baton…

korg250 (again):

In my case it is not about memory usage, but how slow it becomes when it reaches 1 GB of usage.

I will try the about:support tip listed before.

grumpy2:

Out of curiosity, which version of Firefox are you basing this on?

Because the thing about these “I used Firefox until X got too much for me, and I switched” kind of imply something quite significant, which is “I am no longer using Firefox, and can therefore not speak for the possible improvements that have happened since I switched”.

For the last couple of versions, Firefox has shown extremely good memory usage in my experience. And yes, they were absolutely horrible at this in earlier versions, and I’ve been *that* close to switching a number of times because of it. I’ve ranted a lot about how their memory usage was just so broken I doubted they’d ever be able to fix it. But in my experience, they have.

(And yes, this is 120% subjective, and I am certainly not arguing that if your experience differs then you are wrong. But I have noticed a vast improvement in recent versions. As I recall, the first of these fixes started trickling in around the FF13 timeframe, but I could be wrong on that.)

otomo1001:

I think you’ve some other computer issues. Here is my system, 2.4gig firefox process. Still running fine and dandy no slowdown, this is 18 mind you.

http://imgur.com/gNmZK84

korg250 (again):

I am always in the latest version. Was using 18.0.2 until today. Now I am on the 19 after resetting via about:support (still watching how it goes).

Maybe my installation had something wrong and even after the updates the memory issue remained – I don’t know. But I made the “switch” over the last week, when I compared speed between FF and Opera.

korg250 (again):

The reset via about:support worked for me. My FF is running smoothly for over 24 hours. Thanks guys!

Excellent!

Many people have used Firefox for years, and so the chance of mysterious profile problems occurring are quite high.  “Reset Firefox” cleans that dirty slate.  As the support page says, it will “easily fix most problems”.  It’s a simple, one-shot process with a high effectiveness rate that can be explained in a single sentence — perfect for mentioning in an online forum.  (Indeed, I should have linked to the support page in my comment, and then I could have written less explanation.)

Ideally it would also be tried by anyone who tries switching back to Firefox from another browser.  In fact, if Firefox is started up for the first time in a while (3 months? 6 months?) it would be great if it offered to automatically do this.