[rvm-issues] [jira] (RVM-943) MMTk HeapGrowthManager heap growth ratio computation has discontinuities

[David G. (JIRA) <ji...@co...>]

    [ https://jira.codehaus.org/browse/RVM-943?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=288954#comment-288954 ] 

David Grove commented on RVM-943:
---------------------------------

Hi Jeremy.  It looks like the attached patch is corrupted or in an unexpected format.  Could you try again?

thanks,

--dave

                
> MMTk HeapGrowthManager heap growth ratio computation has discontinuities
> ------------------------------------------------------------------------
>
>                 Key: RVM-943
>                 URL: https://jira.codehaus.org/browse/RVM-943
>             Project: RVM
>          Issue Type: Bug
>          Components: MMTk
>         Environment: affects all.
>            Reporter: Jeremy Singer
>            Assignee: David Grove
>            Priority: Minor
>         Attachments: heapsize_patch.tar.gz
>
>
> In HeapGrowthManager.computeHeapChangeRatio(), the current implementation determines the heap size change ratio by a lookup in the 2-dimensional function table (indexed by liveRatio and gcLoad). Given a current liveRatio X and gcLoad Y, the code finds the table rows and columns with nearest values above and below X and Y, then does interpolation from these table lookup values to determine the heap size change ratio.
> However, there is a bug in the interpolation. If X (or Y, respectively) is exactly equal to a row (or column, respectively) label value, then the interpolation still happens, between values in rows (cols) either side of row X (col Y). This leads to discontinuities in the heap sizing function - see attached graphs.
> The submitted patch suppresses interpolation (interpolation correction value becomes 0) in the case where X or Y falls on a label value exactly, so avoiding the discontinuity. 

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