Stupid question

[Vitaly Davidovich]

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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