The mLazyState field is used by XUL generated from RDF templates. Since these nodes are all going to be ``heavyweight'' anyway, there is no reason to store this value in the ``lightweight'' part of the XUL element. (Well, the topmost node in every template also uses the lazy state, so we'd be faulting these nodes -- but the number of these nodes is extremely small.)

So, when bringing up a browser window, 14 out of 1750 nsXULElement objects get their lazy state set: all of these are lightweights. There are 926 heavyweights. nsXULElement is currently (before patch) 17 words, nsXULElements::Slots is 7 words. That means are memory usage is: 1750 * 17 + 926 * 7 = 36232 words With the patch, nsXULElement is 16 words, nsXULElements::Slots is 8 words: 1750 * 16 + (926 + 14) * 8 = 35520 words That's a net savings of 712 words, or about 2%. Hmm. Maybe we should stuff this state into the low bits of a pointer somewhere, so we'd get 1750 * 16 + (926 + 14) * 7 = 34580 words to save 1652 words, or about 4.5%.

Bah, that'd be great to do, but I'll do it once I clean out all the other cruft from the slots.

Comment on attachment 54042 [details] [diff] [review] move mLazyState to nsXULElement::Slots r=shaver. How many bits are used in mLazyState, anyway?

Three. But I'd like to review their usage, too. A lot of that stuff was cooked up on too much caffeine and may be unnecessary.

sr=hyatt

Okay, I've checked in attachment 54042 [details] [diff] [review]. I'll leave this open as a reminder to merge bits once stuff has been cleaned up a bit more.

To save another word in the mSlots, this patch collapses mLazyState and mAttributes: mLazyState takes the low three bits, mAttributes takes the high bits.

Comment on attachment 66021 [details] [diff] [review] collapse mAttributes and mLazyState I tried really hard to find something to complain about here, and came up empty. I guess that means r=shaver.

Comment on attachment 66021 [details] [diff] [review] collapse mAttributes and mLazyState sr=hyatt

Fix checked in.

To be 64-bit safe, you want +#define LAZYSTATE_MASK (((JSWord)1 << LAZYSTATE_BITS) - 1) +#define ATTRIBUTES_MASK (~LAZYSTATE_MASK) (note the (JSWord)1 rather than 1 in the first line). /be

Just made that change. Thanks.