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Better handling for abandonded segments

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This commit is contained in:
Sergiy Kuryata 2024-12-11 17:59:29 -08:00
parent 008bec3013
commit f01f882dd6
1 changed files with 51 additions and 24 deletions
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75
src/segment.c
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@ -1281,6 +1281,7 @@ static void mi_segment_abandon(mi_segment_t* segment, mi_segments_tld_t* tld) {
mi_atomic_exchange_acq_rel(&segment->free_space_mask, free_space_mask);
// remove the free pages from the free page queues
bool hasUsedSmallPage = false;
mi_slice_t* slice = &segment->slices[0];
const mi_slice_t* end = mi_segment_slices_end(segment);
while (slice < end) {
@ -1291,8 +1292,14 @@ static void mi_segment_abandon(mi_segment_t* segment, mi_segments_tld_t* tld) {
slice->block_size = 0; // but keep it free
free_space_mask |= mi_free_space_mask_from_slicecount(slice->slice_count);
}
else if (slice->used < slice->reserved) {
else {
mi_page_t* page = (mi_page_t*)slice;
if (page->block_size <= MI_SMALL_OBJ_SIZE_MAX) {
hasUsedSmallPage = true;
}
if (mi_page_has_any_available(page)) {
free_space_mask |= mi_free_space_mask_from_blocksize(slice->block_size);
}
}
slice = slice + slice->slice_count;
}
@ -1319,12 +1326,16 @@ static void mi_segment_abandon(mi_segment_t* segment, mi_segments_tld_t* tld) {
tld->medium_segment = NULL;
}
else if (segment == tld->large_segment) {
// Clear out small object free space in large segments
tld->large_segment = NULL;
}
if (!hasUsedSmallPage && (segment->page_kind == MI_PAGE_MEDIUM || segment->page_kind == MI_PAGE_LARGE)) {
// Clear out small object free space created by fragmented free slices
free_space_mask = mi_free_space_mask_from_blocksize(MI_SMALL_OBJ_SIZE_MAX);
free_space_mask = free_space_mask | (free_space_mask - 1);
mi_atomic_and_acq_rel(&segment->free_space_mask, ~free_space_mask);
tld->large_segment = NULL;
}
_mi_arena_segment_mark_abandoned(segment);
}
@ -1358,13 +1369,15 @@ static mi_slice_t* mi_slices_start_iterate(mi_segment_t* segment, const mi_slice
}
// Possibly free pages and check if free space is available
static bool mi_segment_check_free(mi_segment_t* segment, size_t slices_needed, size_t block_size, mi_segments_tld_t* tld)
static bool mi_segment_check_free(mi_segment_t* segment, size_t slices_needed, size_t block_size, bool* hasExactPage, mi_segments_tld_t* tld)
{
mi_assert_internal(mi_segment_is_abandoned(segment));
bool has_page = false;
bool hasUsedSmallPage = false;
size_t free_space_mask = 0;
// for all slices
*hasExactPage = false;
const mi_slice_t* end;
mi_slice_t* slice = mi_slices_start_iterate(segment, &end);
while (slice < end) {
@ -1386,12 +1399,20 @@ static bool mi_segment_check_free(mi_segment_t* segment, size_t slices_needed, s
}
free_space_mask |= mi_free_space_mask_from_slicecount(slice->slice_count);
}
else if (mi_page_block_size(page) == block_size && mi_page_has_any_available(page)) {
// a page has available free blocks of the right size
has_page = true;
}
else if (block_size == 0 && mi_page_has_any_available(page)) {
else {
if (page->block_size <= MI_SMALL_OBJ_SIZE_MAX) {
hasUsedSmallPage = true;
}
if (mi_page_block_size(page) == block_size && mi_page_has_any_available(page)) {
// a page has available free blocks of the right size
has_page = true;
*hasExactPage = true;
free_space_mask |= mi_free_space_mask_from_blocksize(page->block_size);
}
else if (mi_page_has_any_available(page)) {
free_space_mask |= mi_free_space_mask_from_blocksize(page->block_size);
}
}
}
else {
@ -1404,8 +1425,8 @@ static bool mi_segment_check_free(mi_segment_t* segment, size_t slices_needed, s
slice = slice + slice->slice_count;
}
if (segment->page_kind == MI_PAGE_LARGE) {
// Clear out small object free space in large segments
if (!hasUsedSmallPage && (segment->page_kind == MI_PAGE_MEDIUM || segment->page_kind == MI_PAGE_LARGE)) {
// Clear out small object free space created by fragmented slices
size_t small_free_space_mask = mi_free_space_mask_from_blocksize(MI_SMALL_OBJ_SIZE_MAX);
small_free_space_mask = small_free_space_mask | (small_free_space_mask - 1);
free_space_mask &= ~small_free_space_mask;
@ -1539,7 +1560,7 @@ static mi_segment_t* mi_segment_try_reclaim(mi_heap_t* heap, size_t needed_slice
size_t free_space_mask = mi_free_space_mask_from_blocksize(block_size);
mi_page_kind_t target_page_kind = mi_page_kind_from_size(block_size);
mi_segment_t* best_candidate_segment = NULL;
int candidates_to_check = 5;
int candidates_to_check = 8;
mi_arena_field_cursor_t current; _mi_arena_field_cursor_init2(heap, &current, free_space_mask);
while ((max_tries-- > 0) && ((segment = _mi_arena_segment_clear_abandoned_next(&current)) != NULL))
@ -1548,8 +1569,9 @@ static mi_segment_t* mi_segment_try_reclaim(mi_heap_t* heap, size_t needed_slice
// todo: should we respect numa affinity for abondoned reclaim? perhaps only for the first visit?
// todo: an arena exclusive heap will potentially visit many abandoned unsuitable segments and use many tries
// Perhaps we can skip non-suitable ones in a better way?
bool hasExactPage = false;
bool is_suitable = _mi_heap_memid_is_suitable(heap, segment->memid);
bool has_page = mi_segment_check_free(segment,needed_slices,block_size,tld); // try to free up pages (due to concurrent frees)
bool has_page = mi_segment_check_free(segment,needed_slices,block_size,&hasExactPage,tld); // try to free up pages (due to concurrent frees)
if (segment->used == 0) {
// free the segment (by forced reclaim) to make it available to other threads.
// note1: we prefer to free a segment as that might lead to reclaiming another
@ -1562,15 +1584,15 @@ static mi_segment_t* mi_segment_try_reclaim(mi_heap_t* heap, size_t needed_slice
// found a large enough free span, or a page of the right block_size with free space
// we return the result of reclaim (which is usually `segment`) as it might free
// the segment due to concurrent frees (in which case `NULL` is returned).
if (segment->page_kind == target_page_kind) {
mi_segment_t* segmentToReturn = mi_segment_reclaim(segment, heap, block_size, reclaimed, tld);
if (segmentToReturn != NULL) {
if (segment->page_kind == target_page_kind && hasExactPage) {
mi_segment_t* segment_to_return = mi_segment_reclaim(segment, heap, block_size, reclaimed, tld);
if (segment_to_return != NULL) {
if (best_candidate_segment != NULL) {
mi_segment_try_purge(best_candidate_segment, true /* true force? */, tld->stats);
_mi_arena_segment_mark_abandoned(best_candidate_segment);
}
mi_segment_increment_reclaimed_stats();
return segmentToReturn;
return segment_to_return;
}
continue;
}
@ -1579,16 +1601,20 @@ static mi_segment_t* mi_segment_try_reclaim(mi_heap_t* heap, size_t needed_slice
best_candidate_segment = segment;
}
else {
if (segment->page_kind < best_candidate_segment->page_kind) {
// Found a better candidate to keep fragmentation low
mi_segment_try_purge(best_candidate_segment, true /* true force? */, tld->stats); // force purge if needed as we may not visit soon again
_mi_arena_segment_mark_abandoned(best_candidate_segment);
mi_segment_t* segment_to_abandon = NULL;
if (segment->page_kind == target_page_kind) {
segment_to_abandon = best_candidate_segment;
best_candidate_segment = segment;
} else if ((best_candidate_segment->page_kind != target_page_kind) && (segment->page_kind < best_candidate_segment->page_kind)) {
segment_to_abandon = best_candidate_segment;
best_candidate_segment = segment;
}
else {
mi_segment_try_purge(segment, true /* true force? */, tld->stats); // force purge if needed as we may not visit soon again
_mi_arena_segment_mark_abandoned(segment);
segment_to_abandon = segment;
}
mi_segment_try_purge(segment_to_abandon, true /* true force? */, tld->stats); // force purge if needed as we may not visit soon again
_mi_arena_segment_mark_abandoned(segment_to_abandon);
}
candidates_to_check--;
@ -1620,10 +1646,11 @@ static mi_segment_t* mi_segment_try_reclaim(mi_heap_t* heap, size_t needed_slice
void _mi_abandoned_collect(mi_heap_t* heap, bool force, mi_segments_tld_t* tld)
{
mi_segment_t* segment;
bool hasExactPage = false;
mi_arena_field_cursor_t current; _mi_arena_field_cursor_init(heap, &current);
long max_tries = (force ? (long)_mi_arena_segment_abandoned_count() : 1024); // limit latency
while ((max_tries-- > 0) && ((segment = _mi_arena_segment_clear_abandoned_next(&current)) != NULL)) {
mi_segment_check_free(segment,0,0,tld); // try to free up pages (due to concurrent frees)
mi_segment_check_free(segment,0,0,&hasExactPage,tld); // try to free up pages (due to concurrent frees)
if (segment->used == 0) {
// free the segment (by forced reclaim) to make it available to other threads.
// note: we could in principle optimize this by skipping reclaim and directly