517858 - Mark stack overflow handling

Status: VERIFIED FIXED

(Tamarin Graveyard :: Garbage Collection (mmGC), defect)

Description

[Lars T Hansen]

Mark stack overflow handling appears to have non-termination problems on a fast linux box in the presence of the patch for bug #495049.

Comment 1

[Lars T Hansen]

Attachment: Scan large objects just once in overflow handler

The large object list was scanned once for each small-object size class, but that's wrong: it should be scanned just once.

Comment 2

[Lars T Hansen]

Attachment: Patch, v2

A bit cleaner.  Tested.

Comment 3

[Lars T Hansen]

(In reply to comment #2)
> Created an attachment (id=401856) [details]
> Patch, v2
> 
> A bit cleaner.  Tested.

pushed pending review: redux changeset: 2566:7ddd7b17ad76

Comment 4

[Ruchi Lohani]

Looks clean.

Comment 5

[Lars T Hansen]

Attachment: Deal properly with OOM in the mark stack

The mark stack has one method, PushSegment, that allocates memory.  That method was set up so that it could fail to allocate memory, but in two cases the failure was not handled properly by the caller: during initialization of the stack, and during transfer of a segment from one stack to the other, where the yielding stack must sometimes allocate a new segment to establish invariants.  This patch cleans that up: failure to allocate during setup is an OOM fault, and failure to allocate on transfer is recoverable and signals the error back to the caller, which makes use of it.

As a consquence, there's some minor refactoring and cleanup elsewhere in the code: the code for forcing a sweep at shutdown (GC::ForceSweep) has been rewritten and factored out of the sweeper as well as out of GC::~GC, and as a result the sweeper can have invariants about the mark and barrier stacks being empty at all times.  The rewrite simplifies the handling of the oom fault in the mark stacks, because that fault propagates into the GC code at fewer points.

Comment 6

[Lars T Hansen]

(In reply to comment #5)
> Created an attachment (id=402052) [details]
> Deal properly with OOM in the mark stack

Pushed pending review: redux changeset:   2582:62b153e02d97

Comment 7

[Chris Peyer]

Resolved fixed engineering / work item that has been pushed.  Setting status to verified.