[webkit-dev] Is there a way to avoid the 16.8 MB RegisterFile memory usage?

[Maciej Stachowiak]

On Aug 26, 2008, at 12:24 AM, Paul Pedriana wrote:

> Thanks for the info about the smaller RegisterFile size; I'll try  
> reducing it for myself and see how it goes.
>
> The RegisterFile.h code has a to-do/fix-me comment for Win32 saying  
> to switch from malloc to VirtualAlloc. FWIW, my vote would be to not  
> make direct calls to OS memory functions within RegisterFile or  
> WebKit in general, at least for non-Unix/Mac builds. Primarily this  
> is because it makes assumptions about what the user wants to do or  
> what the system can do which might not be true. Doing system level  
> memory allocations also prevents the application from measuring  
> memory usage and implementing heap validation. At the least, a user- 
> overridable allocation function can be used and which defaults to  
> using operator new (at least outside Unix variants). This would also  
> have the benefit of allowing the code to work across all platforms  
> out of the box.

WebKit porters are welcome to choose whatever is appropriate for their  
port, taking into account system assumptions. For users of the public  
API, I think explicit allocation control would be kind of dodgy.

> On Windows, VirtualAlloc isn't likely to buy much because AFAIK  
> VirtualAlloc doesn't have the property whereby it commits pages on  
> demand, though it's possible that a future version of Windows may do  
> it.

It doesn't demand-commit but it does let you separate commit and  
reserve, which means you could decommit when exiting JS execution for  
instance.

> However, in the meantime if the user can implement these allocations  
> then it's possible for a user to create a page protected heap that  
> works like the Windows process stack and manually commit upon a page  
> fault. With that approach you can also manually extend the mapped  
> memory beyond the original VirtualAlloc size in case the memory  
> requirement becomes huge.

If the memory requirement gets that big there's probably runaway  
recursion so we're ok with killing the computation.

  - Maciej

>
>
> Thanks.
>
> Paul
>
>
>
>> The RegisterFile is the amount of memory available on the JS stack,
>> reducing it directly reduces the amount of stack, and hence  
>> recursion,
>> that js code can do.  That said, the RegisterFile allocation should
>> result in delayed paging -- eg. it should only be reserving address
>> space, and the OS won't actually allocate memory until we attempt to
>> use it.  At least if mmap exists and is usable.
>>
>> --Oliver
>>
>> On Aug 25, 2008, at 5:25 PM, Cedric Vivier wrote:
>>
>>
>>> On Tue, Aug 26, 2008 at 12:04 AM, Geoffrey Garen <ggaren at apple.com>
>>> wrote:
>>>
>>>> If you want the RegisterFile to be 512K, just change its size to
>>>> 512K.
>>>> You can even deallocate it after JavaScript finishes executing, if
>>>> that helps.
>>>>
>>> I am curious as well as Mark, what are the consequences of  
>>> decreasing
>>> (or increasing) this value ? [besides the memory usage of course]
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>>>
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>>
>
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