RFR (XXS): 8079156: 32 bit Java 9-fastdebug hit assertion in client mode with StackShadowPages flag value from 32 to 50

[Vladimir Kozlov]

You are right but we don't want spent too much time on this. Code will become more complex than current. And since with 
grow() we usually double size we may consume more memory than with current guess.

Vladimir

On 7/14/15 8:00 AM, gerard ziemski wrote:
>
> On 07/13/2015 07:42 PM, Vladimir Kozlov wrote:
>> On David's question. The size of code is rounded to 64 bytes (minimum allocation unit in CodeCache). So you don't need
>> to rounding.
>>
>> We do calculate additional padding on sparc taking into account instructions sizes and number of StackShadowPages
>> pages (which banging code is looping on):
>>
>> #ifdef ASSERT
>>   if (UseStackBanging) {
>>     pad += StackShadowPages*16 + 32;
>>   }
>> #endif
>>
>> But on x86 we have variable instructions size so it is not easy pre-calculate it.
>> So we simple set big number and if we hit the assert in codeBuffer.hpp we increase it:
>
> It sounds like we had to do this before.
>
> Why does CodeBuffer require the space requirements in advance? Wouldn't it be more robust to leave it up to the
> CodeBuffer to figure out the exact memory size needed and avoid situations like this? It seems fragile to have to guess
> how big we need it and hope we don't hit the assert with all the bells and whistles turned on.
>
>
> cheers