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Firefox Memory Leak is a Feature
SenseOfHumor writes "The Firefox memory leak is not a bug. It's a feature! The 'feature' is how the pages are cached in a tabbed environment." From the article: "To improve performance when navigating (studies show that 39% of all page navigations are renavigations to pages visited less than 10 pages ago, usually using the back button), Firefox 1.5 implements a Back-Forward cache that retains the rendered document for the last five session history entries for each tab. This is a lot of data. If you have a lot of tabs, Firefox's memory usage can climb dramatically. It's a trade-off. What you get out of it is faster performance as you navigate the web."
So there's a way to limit the number of cached pages per tab, but no way to limit the total number of cached pages, for those of us who have fifteen tabs open?
Whoops!
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If this is true, then why is so little memory freed after the tab is closed, compared with how much it consumed when it was created?
If you don't know where you are going, you will wind up somewhere else.
Why does Opera do the same thing faster without the memory penalties?
FanFictionRecs.net
Before someone jumps at my throat, it's just a description what I'd like to see, but of course its all up to the developers, they decide what to code and do with their time. It is just simple user feedback.
It takes a man to suffer ignorance and smile
Be yourself no matter what they say
Uh, using a lot of memory is not the same as a memory leak.
> Wouldn't all pointer references then have to go through some kind of lookup table, so that the objects could be relocated by the runtime without breaking them?
Only on a computer without virtual memory. In a PC (which *has* virtual memory), you just punch holes in the memory.
What happens is a process gets an "address space", into which pointers can point, but any given address may not map onto some real storage. The process asks the operating system to map a range of addresses onto real storage which the operating system will try to map to real fast memory when it thinks it will be used at any moment. When the OS figures the memory wont be needed for a while, and something else needs some memory, the OS copies the data to disk and redirects the mapping to a proxy that will pull the data back into memory when the process tries to use it again.
When a process knows that it won't need a section of that real storage, it can tell the operating system to unmap it from the address space.
There are various other things that go on, but that's the simple story. From a figure posted in an earlier message, it seems that opera does pretty damned well (in comparison to most modern programs) with just the simple story, not having to rely much on nasty unreliable heuristics. Of that I am impressed.
Excellent post, well worth the +5.
But you pointed out the flaw in the wording of the article - this IS NOT a memory leak, just inefficient use of the heap.
I thought the definition of a memory leak was an application that kept allocating memory from the OS as it ran, not an application that asked for a chunk of memory and just reused it inefficiently?
(If I'm wrong, someone please correct me).
A Man's ethical behavior should be based effectually on sympathy, education, and social ties -- Albert Einstein
Memory isn't an unlimited resource you just hoard whenever you think you need it. Right now my instance of firefox is taking up 128 megs! I've seen it up to 256 megs before. This is just simply insane. I've seen people who's computer performance has gone down the tubes because firefox is taking up all the memory (and these are machines with 512 megs of memory, not exactly tiny). What I'd like to convey to the firefox devs is this: Your application isn't the only one running on the system. Play nice and don't be a hog.
With the number of people complaining about this (and the number of people that don't even KNOW to complain) isn't it a safe bet that you've made a mistake in the amount of cached pages?
AccountKiller
Virtual memory is not a carte blanche for memory hogging. As you should know, memory hogging will result in degraded performance.
Assuming that users have unlimited resources is exactly how Mozilla is barely usable on Windows 95-ME - especially when you have Slashdot Moderator access.
In an ideal situation, that would be correct.
However, the operating system does not know which memory is currenly "in use" and which ones are "in cache" - in fact, it's quite easy for an "in use" to be physically sandwiched between two "in cache" entries. Because of this, you will have a sudden loading time if you do plenty of other tasks in the background and suddenly switch back to Mozilla.
Small applications, being small, do not generally have to wait 1/2 seconds to recover from being pages in or out. Since Mozilla allocates the cache in memory, it will have to wait those two seconds.
An OS with decent vmem support would allow you to map files to memory. This results in no swapping at all - only writing perodic output to the hard drive, and loading the file into memory as required. If another application needs more memory, the memory map is discarded with no need to write the contents of memory.
An application that doesn't exploit the usage of memory maps is as good as an OS with shoddy vmem support. (Of course, it can simply use it's disk cache for the same effect.)