Web Apocrypha

Last year I got a Nokia N9 on Qt Developer Days, it's a great mobile phone, I really like it, but I haven't published any memory measurement results about it yet. In my last post I did WebKit memory profiling on it with Valgrind, but it was all about heap usage. I think a number of persons are interested in the overall memory usage such as peak memory usage, the sizes of the used libraries, etc. During QtWebKit's life-cycle we switch from one library to another, usually because of performance considerations. In the past we do not take too much attention to memory consumption-related topics while switching between libraries, although it would be very vital to keep eye on this area as well.

The main focus of my next experiment is yet another allocator called TLSF (Two-Level Segregate Fit). Based on the info published on its website, TLSF has bounded response time, efficient allocation methods which are fast enough, and it has efficient memory usage. Furthermore, the site promises quite good memory fragmentation values. Can it demonstrate all this inside WebKit?

After I benchmarked JavaScriptCore with our new participant called DLmalloc, it has been suggested to test it with QtLauncher also. I compiled DLmalloc in thread-safe mode (USE_LOCKS=1), so it became capable to serve WebCore's memory requests. Perhaps, another solution could have been to turn off every use of threads in QtLauncher/WebCore, but I think this would be a lucky approach...

There are a lot of custom allocators in the world, so let's try another promising one, called DLmalloc. It was made by Doug Lea. I've put DLmalloc into JavaScriptCore with the help of the custom allocation framework. I tested DLmalloc only in JavaScriptCore, because it didn't work well with QtWebKit's multi-threaded features. The measurements have been made with QtWebKit, running on x86 Debian-Lenny.

 

Since, two of our tested allocators - TCmalloc, JEmalloc - benefit in multi-threaded environment, I did some benchmark which uses threading effectively. I run 2 instances of each popular benchmarks simultaneously with the help of JavaScript workers. I benchmarked on Linux-Qt port of WebKit and used official r54475 revision. All measurements were running in QtLauncher and did minimal painting only.

JEmalloc is a highly scalable memory allocator made by Jason Evans. This is the default allocator of the FreeBSD operating system and Firefox's Linux/Windows versions, but how does it perform in WebKit?

It took a while but now I'm happy to announce that all core classes are inherited from FastAllocBase in WebCore. Further the previous changes in JavaScriptCore, by now almost the whole world is a subclass of FastAllocBase. :-)