• Dominik Inführ's avatar
    [heap] Remove sweeping_slot_set_ from MemoryChunk · ca505562
    Dominik Inführ authored
    Since the new space is always empty after a full GC, the old-to-new
    remembered set is also always empty after a full GC. This means we can
    get rid of the sweeping_slot_set_.
    
    This slot set was used to allow the main thread to insert into the
    old-to-new remembered set non-atomically. The sweeping slot set was
    owned by the sweeper, which deletes slots in free memory from it. The
    main thread would start with an empty old-to-new remembered set. After
    sweeping both slot sets are merged again.
    
    The sweeper now needs to behave differently during a GC. When sweeping
    a page during full GC, the sweeper needs to delete old-to-new-slots in
    free memory.
    
    Outside of the GC the sweeper isn't allowed to remove from the
    old-to-new slots anymore. This would race with the main thread that adds
    slots to that remembered set while the sweeper is running. However,
    there should be no recorded slots in free memory. DCHECKing this is
    tricky though, because we would need to synchronize with the main
    thread right-trimming objects and at least String::MakeThin only deletes
    slots after the map release-store.
    
    Bug: v8:12760
    Change-Id: Ic0301851a714e894c3040595f456ab93b5875c81
    Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3560638Reviewed-by: 's avatarMichael Lippautz <mlippautz@chromium.org>
    Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
    Cr-Commit-Position: refs/heads/main@{#79713}
    ca505562
spaces.cc 16.3 KB