[Webkit-unassigned] [Bug 26998] New: Decommitted spans are added to the list of normal spans rather than the returned spans in TCMalloc_PageHeap::Delete()

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=26998

           Summary: Decommitted spans are added to the list of normal
                    spans rather than the returned spans in
                    TCMalloc_PageHeap::Delete()
           Product: WebKit
           Version: 528+ (Nightly build)
          Platform: PC
        OS/Version: Mac OS X 10.5
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: New Bugs
        AssignedTo: webkit-unassigned at lists.webkit.org
        ReportedBy: adachan at apple.com


In TCMalloc_PageHeap::Delete(), the deleted span can be decommitted (memory
released back to the system) in the process of merging with neighboring spans
that are also decommitted.  The merged span needs to be placed in the list of
returned spans (spans whose memory has been returned to the system).  Right now
it's always added to the list of the normal spans which can theoretically cause
thrashing.  The purpose of tracking normal and returned spans is so when we
need to return a free span of a certain size, we'll pick a span whose memory is
already committed before a span whose memory has been decommitted and needs to
be re-committed before returning.  By placing a decommitted span in the normal
span list, we break this optimization.

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