Re: [rvm-research] How to record objects' read/write times

I get it.
Thank you  very much!

On Tue, Jun 2, 2015 at 10:42 AM, Robin Garner <[email protected]> wrote:
> On 01/06/15 19:51, 王晨曦 wrote:
>> Hi ,robin
>>
>>   I have checked the function  collectionRequired() in Gen.java again,
>> I think I understand the nursery's initial size.（The question 1））
>>
>> The function virtualMemoryExhausted() can control the initial size of nursery.
>>
>> private boolean virtualMemoryExhausted() {
>>      return ((int)(getCollectionReserve() * WORST_CASE_COPY_EXPANSION))
>>> = getMaturePhysicalPagesAvail();
>>    }
>>
>> WORST_CASE_COPY_EXPANSION = 1.5f
>>
>> So,I think in the begin ,the ratio of nursery / immix can't exceed
>> 1/1.5 ; Or It will trigger a minor GC.
>> So,I guess the initial nursery size is less than 1/2.5 (40%) of the
>> initial heap.(The initial heap size is 50M, I have seen.)
>> May be other space occupy some heap, so the initial nursery size is 16M.
>>
>> Is this right?
>
> I haven't checked your calculation, but yes - this is what's going on:
> MMTk makes judgements about when to collect based on the status of the
> entire heap (of which the nursery is a part), not just on the size of
> the nursery.
>
> The virtualMemoryExhausted() check catches an edge case where the size
> of the heap gets close to the virtual address space available for the
> mature space - in a 50m heap it's not going to come into play.
>
> So if the bounded nursery is 32M and the heap is only 50M, the nursery
> can never reach 32M - it will get to 50/3 at most.  If you increase the
> heap size (-Xms200m for example), the nursery will reach its bound for
> many collections, until the mature space makes it impossible.
>
>> On Sun, May 31, 2015 at 6:44 PM, 王晨曦 <[email protected]> wrote:
>>> Hi,Robin
>>>
>>> Thank you for your help very much!!   I have confirmed what you have
>>> said. I can get most of them.
>>> But I still have some doubts that I can't understand.
>>>
>>>
>>>>
>>>>> 1)
>>>>> So,my first  doubt is   I can't find which variable to describe the
>>>>> "the nursery size is set to 1/2 the available heap size ".
>>>>> I mean the program set which variable to control this ?
>>>>> May be the nursery size is set as the min of the range
>>>>> (fixedNursery.value) ,and round to the max size (boundedNursery.value)
>>>>> when the program is running ?
>>>>
>>>> Look at the method Plan#getPagesReserved().
>>>
>>> 1）
>>> I have read this function, I think this function is about to get the
>>> current reserved pages. I can't find its connection with the Nursery's
>>> initial size in GenImmix.
>>>
>>> But I really have seen that the nursery's initial size is 16M, half of
>>> the nursery's max size( default max size is 32M).
>>>
>>>
>>>>
>>>> No, all spaces dynamically resize, but they don't change their virtual
>>>> memory.  When we use a nursery in high memory, the base virtual address
>>>> of the nursery is fixed at build time.  When we talk about "resizing"
>>>> spaces, we simply mean using more or less of the space that has been set
>>>> aside.
>>>>
>>>
>>> 2)
>>> I have read the functions about how to manage the nursery space
>>> (GenImmix config).
>>> In my opinion ,The nursery is a MonotonePageResource , and the nursery
>>> space is allocated in the top of the heap.
>>> But,when allocate pages ,the nursery's allocator will start from the
>>> nursery's  low address ( Monotone.cursor / nursery.start ) to the heap
>>> end ( Monotone.sentinel ).
>>> And the nursery's virtual memory will not be occupied by other
>>> discontiguous space,even if the nursery only use little of it.
>>>
>>> Are these right?
>
> Exactly.  The overall heap layout looks something like
>
> |<- VM ->| |<------ Discontiguous spaces---->|<- Nursery->|
>
> unless you enable discontiguous nursery spaces.
>
>>>
>>>
>>> Than you !
>>>
>>>
>>> --
>>> ChenXi.Wang
>>
>>
>>
>
>
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-- 
ChenXi.Wang

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