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8344853: Parallel: Improve comments in psParallelCompact

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Reviewed-by: sjohanss, zgu
This commit is contained in:
Albert Mingkun Yang 2024-11-26 08:55:01 +00:00
parent 57d35f98f6
commit 9793e73bc1
1 changed files with 16 additions and 16 deletions
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32
src/hotspot/share/gc/parallel/psParallelCompact.cpp
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@ -362,8 +362,9 @@ HeapWord* ParallelCompactData::summarize_split_space(size_t src_region,
split_info.record(split_region, overflowing_obj, preceding_live_words);
HeapWord* src_region_start = region_to_addr(src_region);
HeapWord* new_top = destination - pointer_delta(src_region_start, overflowing_obj);
// The [overflowing_obj, src_region_start) part has been accounted for, so
// must move back the new_top, now that this overflowing obj is deferred.
HeapWord* new_top = destination - pointer_delta(region_to_addr(src_region), overflowing_obj);
// If the overflowing obj was relocated to its original destination,
// those destination regions would have their source_region set. Now that
@ -890,7 +891,7 @@ void PSParallelCompact::summary_phase()
_summary_data.summarize_dense_prefix(old_space->bottom(), dense_prefix_end);
}
// Compacting objs inn [dense_prefix_end, old_space->top())
// Compacting objs in [dense_prefix_end, old_space->top())
_summary_data.summarize(_space_info[id].split_info(),
dense_prefix_end, old_space->top(), nullptr,
dense_prefix_end, old_space->end(),
@ -1596,9 +1597,9 @@ void PSParallelCompact::forward_to_new_addr() {
&start_region, &end_region);
for (size_t cur_region = start_region; cur_region < end_region; ++cur_region) {
RegionData* region_ptr = _summary_data.region(cur_region);
size_t live_words = region_ptr->partial_obj_size();
size_t partial_obj_size = region_ptr->partial_obj_size();
if (live_words == ParallelCompactData::RegionSize) {
if (partial_obj_size == ParallelCompactData::RegionSize) {
// No obj-start
continue;
}
@ -1606,19 +1607,18 @@ void PSParallelCompact::forward_to_new_addr() {
HeapWord* region_start = _summary_data.region_to_addr(cur_region);
HeapWord* region_end = region_start + ParallelCompactData::RegionSize;
if (split_info.is_split(cur_region)) {
// Part 1: will be relocated to space-1
HeapWord* preceding_destination = split_info.preceding_destination();
HeapWord* split_point = split_info.split_point();
forward_objs_in_range(cm, region_start + live_words, split_point, preceding_destination + live_words);
forward_objs_in_range(cm, region_start + partial_obj_size, split_point, preceding_destination + partial_obj_size);
// Part 2: will be relocated to space-2
HeapWord* destination = region_ptr->destination();
forward_objs_in_range(cm, split_point, region_end, destination);
} else {
HeapWord* destination = region_ptr->destination();
forward_objs_in_range(cm, region_start + live_words, region_end, destination + live_words);
forward_objs_in_range(cm, region_start + partial_obj_size, region_end, destination + partial_obj_size);
}
}
}
@ -1984,11 +1984,11 @@ HeapWord* PSParallelCompact::skip_live_words(HeapWord* beg, HeapWord* end, size_
}
}
// On filling a destination region (dest-region), we need to know the location
// of the word that will be at the start of the dest-region after compaction.
// A dest-region can have one or more source regions, but only the first
// source-region contains this location. This location is retrieved by calling
// `first_src_addr` on a dest-region.
// On starting to fill a destination region (dest-region), we need to know the
// location of the word that will be at the start of the dest-region after
// compaction. A dest-region can have one or more source regions, but only the
// first source-region contains this location. This location is retrieved by
// calling `first_src_addr` on a dest-region.
// Conversely, a source-region has a dest-region which holds the destination of
// the first live word on this source-region, based on which the destination
// for the rest of live words can be derived.
@ -2017,9 +2017,9 @@ HeapWord* PSParallelCompact::skip_live_words(HeapWord* beg, HeapWord* end, size_
// ^ ^
// | old-space-end | eden-space-start
//
// Therefore, in this example, region-n will have two dest-regions, one for
// the final region in old-space and the other for the first region in
// eden-space.
// Therefore, in this example, region-n will have two dest-regions:
// 1. the final region in old-space
// 2. the first region in eden-space.
// To handle this special case, we introduce the concept of split-region, whose
// contents are relocated to two spaces. `SplitInfo` captures all necessary
// info about the split, the first part, spliting-point, and the second part.