Heap should not continually allocate new pages in steady state

• Component: JavaScriptCore
• Status: RESOLVED FIXED

[Mark Hahnenberg]

Currently, in steady state (i.e. a constant amount of live GC memory with a constant rate of allocation) assuming we've just finished a collection with X live blocks in CopiedSpace, we increase our working set by X blocks in CopiedSpace with each collection we perform. This is due to the fact that we allocate until we run out of free blocks to use in the Heap before we consider whether we should run a collection. 

In the longer term, this issue will be mostly resolved by implementing quick release for the CopiedSpace. In the shorter term, we should change our policy to check whether we should allocate before trying to use a free block from the Heap. We can change our policy to something more appropriate once we have implemented quick release.

This change should also have the convenient side effect of reducing the variance in GC-heavy tests (e.g. v8-splay) due to fact that we are doing less VM allocation during copying collection.

[Mark Hahnenberg]

Created attachment 140837 [details]
Patch

[Mark Hahnenberg]

Comment on attachment 140837 [details]
Patch

This patch was already r+ed by Geoff Garen (ggaren).

[Mark Hahnenberg]

Landed in http://trac.webkit.org/changeset/116484