1.4.2 PrintFLSStatistics Output

[Neeraj Jain]

Thanks Ramki. This has cleared lots of our doubts. To complete the
discussion I have one more query left in the same context.

We have seen the YG promotions succeeding with BinaryTreeDictionary
containing Max Chunk Sizes as small as 600 words (4800 bytes) though Total
Free Space was much higher. Does that mean that, in addition to not
requiring space to accommodate full Eden+From spaces, java 1.4.2_17 no
longer has the constraint needing "*single contiguous memory chunk*" also to
accommodate all the promoted objects in old generation?

Regards,
Neeraj

On Tue, Aug 19, 2008 at 11:12 PM, Y Srinivas Ramakrishna <
Y.S.Ramakrishna at sun.com> wrote:

>
> Hi Neeraj --
>
> Good question; this has come up in another recent discussion on
> this list.
>
> > I still have a query on your answer to question #2. As I understand,
> > for a
> > YG promotion to be successful GC needs a contiguous memory chunk equal
> > to
> > the sum of sizes of Eden and From space which comes out to be approx.
> > 230 MB
> > in our case. The total free space in the "BinaryTreeDictionary"
> containing
> > larger blocks is only ~2.8 MB but the promotions are still succeeding.
> >
> > My question is: *where the GC is getting the contiguous memory chunk
> > of 230
> > MB from?*
>
>
> That was indeed the old constraint in the early versions of 1.4.2,
> which was fixed in some early version of 5.0 (if i recall correctly) so
> that we could handle "promotion failure" (where mid-scavenge we
> discover that we have no space in the old gen to promote a live
> object from the young gen). That code was subsequently also backported
> to some version of 1.4.2, probably 1.4.2_11 or later (i am not
> sure precisely which version, but can find out if you really care).
> As a result, (at least) in 1.4.2_17, in fact, there isn't such a
> restriction,
> and scavenges will occur even in the absence of the pessimal "full
> promotion guarantee".
>
> -- ramki
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://mail.openjdk.java.net/pipermail/hotspot-gc-use/attachments/20080820/f3a7e73f/attachment.html