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Date: Wed, 23 Jan 2008 12:02:28 +0300
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To: Nuno Lopes <nlopess@php.net>
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Subject: Re: [PHP-DEV] Segmented argument_stack
From: dmitry@zend.com (Dmitry Stogov)

Hi Nuno,

Thank you for your notes.

Nuno Lopes wrote:
> Hi Dmitry,
> 
> The patch looks fine. Although it wastes a bit more memory than the 
> current implementation, I think it's ok.

I think the patch uses exactly the same amount of memory, except that 
the current implementation uses CPU stack and the patch uses ZE heap.

> It also has some memory 
> fragmentation, which shouldn't be an issue (we don't have functions with 
> 100 arguments :P).

Functions with 100 (or 10000 :) arguments might work slower, but anyway 
it's an unusual case.

> 
> As a side note, I think the following code could be optimized:

Probably it could, but note that the code not just moves the stack 
pointer, but also destroys arguments there (zval_ptr_dtor).

> + while (zend_vm_stack_top(TSRMLS_C) != stack_frame) {
> + zval *stack_zval_p = zend_vm_stack_pop(TSRMLS_C);
> + zval_ptr_dtor(&stack_zval_p);
>  }
> 
> I think you can simply discard the last n ptrs on the stack. A 
> zend_vm_stack_pop(num_elements) would do the trick (or a 
> zend_vm_stack_pop_until(stack_frame)). That way the function call 
> cleanup would be a little faster.

May be I misunderstood you. Lets commit unmodified patch and then you'll 
show me a way to optimize it.

Thanks. Dmitry.


> Thanks,
> Nuno
> 
> 
> ----- Original Message ----- From: "Dmitry Stogov" <dmitry@zend.com>
> To: "PHP Internals List" <internals@lists.php.net>
> Sent: Monday, January 21, 2008 7:47 PM
> Subject: [PHP-DEV] Segmented argument_stack
> 
> 
>> Hi,
>>
>> The attached patch (for PHP_5_3) implements the segmented argument_stack
>> that has the following advantages:
>>
>> 1) It fixes #43426 and other crashes which occur because of stack
>> reallocation.
>>
>> 2) The whole stack is never reallocated. So we don't have penalties
>> because of the while stack copying (it may be 1MB and more).
>>
>> 3) CPU stack usage reduced, because execute_data, Ts and CVs now are
>> stored in the same argument_stack. As result the probability of CPU
>> stack overflow is reduced.
>>
>> 4) func_num_args(), func_get_agr(), func_get_args(),
>> debug_print_backtrace() and exception's backtrace now always able to get
>>  arguments. They didn't work before in case of incomplete "arguments
>> frame". For example: "foo(1, func_num_args());".
>>
>> 5) bench.php got about 1% speedup
>>
>> I'm going to commit the patch into HEAD and PHP_5_3 on Thursday.
>> Any objections?
>>
>> Thanks. Dmitry. 
> 
>