1. 31 Jul, 2020 1 commit
    • Dan Elphick's avatar
      [heap] Share RO_SPACE pages with pointer compression · c7d22c49
      Dan Elphick authored
      This allows the configuration v8_enable_shared_ro_heap and
      v8_enable_pointer_compression on Linux and Android, although it still
      defaults to off.
      
      When pointer compression and read-only heap sharing are enabled, sharing
      is achieved by allocating ReadOnlyPages in shared memory that are
      retained in the shared ReadOnlyArtifacts object. These ReadOnlyPages are
      then remapped into the address space of the Isolate ultimately using
      mremap.
      
      To simplify the creation process the ReadOnlySpace memory for the first
      Isolate is created as before without any sharing. It is only when the
      ReadOnlySpace memory has been finalized that the shared memory is
      allocated and has its contents copied into it. The original memory is
      then released (with PC this means it's just released back to the
      BoundedPageAllocator) and immediately re-allocated as a shared mapping.
      
      Because we would like to make v8_enable_shared_ro_heap default to true
      at some point but can't make this conditional on the value returned by
      a method in the code we are yet to compile, the code required for
      sharing has been mostly changed to use ifs with
      ReadOnlyHeap::IsReadOnlySpaceShared() instead of #ifdefs except where
      a compile error would result due to the absence of a class members
      without sharing. IsReadOnlySpaceShared() will evaluate
      CanAllocateSharedPages in the platform PageAllocator (with pointer
      compression and sharing enabled) once and cache that value so sharing
      cannot be toggled during the lifetime of the process.
      
      Bug: v8:10454
      Change-Id: I0236d752047ecce71bd64c159430517a712bc1e2
      Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2267300
      Commit-Queue: Dan Elphick <delphick@chromium.org>
      Reviewed-by: 's avatarIgor Sheludko <ishell@chromium.org>
      Reviewed-by: 's avatarUlan Degenbaev <ulan@chromium.org>
      Cr-Commit-Position: refs/heads/master@{#69174}
      c7d22c49
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