• Ulan Degenbaev's avatar
    [heap] New live byte tracking. · dfc6b4dd
    Ulan Degenbaev authored
    This patch changes how space size and capacity are updated in GC:
    - space capacity changes only when a page added/removed from the space.
    - space size is reset to zero before sweeping and incremented by
      page->live_bytes_count_ for each to-be-swept page.
    - space size is refined after sweeping using the accurate
      page->allocated_bytes counter produces by the sweeper.
    
    Invariants:
    1. space.capacity = sum [page.size | for page in space].
    2. After marking, before sweeping:
       a) space.size = sum [page.live_bytes_count | for page in space].
    3. After sweeping, before marking ends:
       a) space.size = sum [page.allocated_bytes | for page in space].
       b) page.allocated_bytes >= (sum [object.size | for object in page] +
             page.linear_allocation_area).
       c) page.area_size = (page.allocated_bytes + page.wasted_memory +
             sum [free_list_entry.size | for free_list_entry in page].
    
    3.b becomes equality if the mutator is not doing array trimming,
    object slack tracking during sweeping.
    
    Bug: chromium:694255
    Change-Id: Ic8d16a8171187a113fee2df8bf3c2a4c5e77bc08
    Reviewed-on: https://chromium-review.googlesource.com/618889
    Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
    Reviewed-by: 's avatarMichael Lippautz <mlippautz@chromium.org>
    Cr-Commit-Position: refs/heads/master@{#47409}
    dfc6b4dd
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