Stupid question

[Vitaly Davidovich]

can you add a print statement to commit_memory() to see what arguments are
being passed to it? I'm sure someone on this mailing list will have a
better suggestion, but that's what I'd try just to establish that some code
is indeed trying to expand the heap to its max allotted size.

Sent from my phone
On May 22, 2012 4:08 PM, "Greg Bowyer" <gbowyer at fastmail.co.uk> wrote:

> **
> Yes thats basically it
>
> java -Xms512m -Xmx9g test
>
> On 22/05/12 12:27, Vitaly Davidovich wrote:
>
> Hi Greg,
>
> As an aside, in os::commit_memory, I think the tertiary condition that
> sets the flags is inverted - you want MAP_LOCKED if LockHeapInMemory is
> set, I believe.
>
> As to your question, what args are being passed to the above function in
> your run? I take it -Xms is less than Xmx in your trial?
>
> Sent from my phone
> On May 22, 2012 3:07 PM, "Greg Bowyer" <gbowyer at fastmail.co.uk> wrote:
>
>> Not sure if this is the right venue for this, or if I am insane
>>
>> I have been playing with the openjdk code with a view to lock the heap in
>> memory (or at least suggest to the OS that it wants to be locked in memory).
>>
>> My use case is for java processes that are greedy in memory and typically
>> have a virtual size larger than physical ram. This is not where an end user
>> allocates a java heap beyond ram but rather things like Lucene / Cassandra,
>> where typically the JVM heap is large but limited to say 1/4 of the total
>> physical ram and the rest of the process virtual size is taken up with
>> mmap()'d files.
>>
>> There are java projects that currently do this with a call out via JNA /
>> JNI to mlockall()
>>
>> Asking the OS to use the MAP_LOCKED flag in the mmap calls in
>> os_linux.cpp effectively does an mlock / mlockall which I think means that
>> when the OS chooses pages to page out; then it should (for some measure of
>> should) avoid paging out the JVM heap.
>>
>> This means that horrors between CMS and paging do not cause hateful
>> pauses (hopefully)
>>
>> The thing I cant understand is that when I start a new VM with this code
>> (attached) it appears to lock the full size of the heap (-Xmx) (even though
>> the given memory is not used by the VM), this seems to make the entire
>> space resident.
>>
>> any ideas ?
>>
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>>
>>
>
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