diff options
| -rw-r--r-- | runtime/gc/collector/mark_compact.cc | 31 |
1 files changed, 24 insertions, 7 deletions
diff --git a/runtime/gc/collector/mark_compact.cc b/runtime/gc/collector/mark_compact.cc index 85e6a5fffa..c9566c0c3f 100644 --- a/runtime/gc/collector/mark_compact.cc +++ b/runtime/gc/collector/mark_compact.cc @@ -3519,9 +3519,30 @@ void MarkCompact::CompactionPhase() { RecordFree(ObjectBytePair(freed_objects_, freed_bytes)); } + size_t moving_space_size = bump_pointer_space_->Capacity(); + size_t used_size = (moving_first_objs_count_ + black_page_count_) * kPageSize; if (CanCompactMovingSpaceWithMinorFault()) { CompactMovingSpace<kMinorFaultMode>(/*page=*/nullptr); } else { + if (used_size < moving_space_size) { + // mremap clears 'anon_vma' field of anonymous mappings. If we + // uffd-register only the used portion of the space, then the vma gets + // split (between used and unused portions) and as soon as pages are + // mapped to the vmas, they get different `anon_vma` assigned, which + // ensures that the two vmas cannot merged after we uffd-unregister the + // used portion. OTOH, registering the entire space avoids the split, but + // unnecessarily causes userfaults on allocations. + // By mapping a zero-page (below) we let the kernel assign an 'anon_vma' + // *before* the vma-split caused by uffd-unregister of the unused portion + // This ensures that when we unregister the used portion after compaction, + // the two split vmas merge. This is necessary for the mremap of the + // next GC cycle to not fail due to having more than one vmas in the source + // range. + uint8_t* unused_first_page = bump_pointer_space_->Begin() + used_size; + // It's ok if somebody else already mapped the page. + ZeropageIoctl(unused_first_page, /*tolerate_eexist*/ true, /*tolerate_enoent*/ false); + UnregisterUffd(unused_first_page, moving_space_size - used_size); + } CompactMovingSpace<kCopyMode>(compaction_buffers_map_.Begin()); } @@ -3535,13 +3556,9 @@ void MarkCompact::CompactionPhase() { for (uint32_t i = 0; compaction_in_progress_count_.load(std::memory_order_acquire) > 0; i++) { BackOff(i); } - - size_t moving_space_size = bump_pointer_space_->Capacity(); - UnregisterUffd(bump_pointer_space_->Begin(), - minor_fault_initialized_ ? - (moving_first_objs_count_ + black_page_count_) * kPageSize : - moving_space_size); - + if (used_size > 0) { + UnregisterUffd(bump_pointer_space_->Begin(), used_size); + } // Release all of the memory taken by moving-space's from-map if (minor_fault_initialized_) { if (IsValidFd(moving_from_space_fd_)) { |