well, it doesn't feel like memory hog due to having many processes. when you close all those tabs the memory is freed.

for some unknown to me reason after having few sites open in Safari and closing everything, it still takes up 500MB in memory.

in short, you have to restart Safari to free-up memory. with Chrome closing tabs is sufficient.

My general view is that I don't mind something being a memory hog if it's using that memory to make my experience really fast (which chrome does).

Being a memory hog AND being slow really just makes me hate the software (Firefox - although I hear it's getting better in 4+ which I have not tried).

I think almost all tests(as difficult as it is to measure) show firefox coming in with the least amount of memory usage.

The sites are still cached in-memory for fast history browsing.

Is that really where all of the memory goes? On a normal consumer-grade HDD a disk seek is ~10ms and reading a megabyte sequentially is another 10ms or so. Conservatively speaking it should be possible to load a site from the disk cache in under 50ms, and in practice that would probably be quite a bit faster (especially if the data is in the page cache). With that kind of speed it would make sense to persist these caches on disk if a page isn't actually opened in any tabs.

I don't know if data like this exists in an easily understandable format (i.e. not just cryptic massif dumps that would only make sense to WebKit hackers), but it would be interesting to see a heap profile of a WebKit/Safari session to see what's using all of the memory in an "empty" browser session.

Fast history browsing is useful only when clicking the back button. Caching the sites after tabs are closed is just a bad design, no excuses.

Fast history browsing is plenty useful when undoing a closed tab. Not sure if Safari does this, but on Firefox if you undo a closed tab, the tab comes back exactly as it was before, with history intact. I use that feature quite a bit.

it works like this with Chrome too, but without keeping all the stuff in RAM.