1.4.2 PrintFLSStatistics Output

[Y Srinivas Ramakrishna]

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
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