From e628fc70676e8e2176fe66e8275480c14ad29ca3 Mon Sep 17 00:00:00 2001 From: daan Date: Sun, 26 Jan 2020 12:39:11 -0800 Subject: [PATCH] cleanup reclaim logic --- include/mimalloc-internal.h | 24 +++----- src/page.c | 40 +++++------- src/segment.c | 117 +++++++++++++++++++----------------- 3 files changed, 87 insertions(+), 94 deletions(-) diff --git a/include/mimalloc-internal.h b/include/mimalloc-internal.h index 902d2fd..c7d7a1d 100644 --- a/include/mimalloc-internal.h +++ b/include/mimalloc-internal.h @@ -411,30 +411,24 @@ static inline mi_thread_free_t mi_tf_set_block(mi_thread_free_t tf, mi_block_t* return mi_tf_make(block, mi_tf_delayed(tf)); } -// are all blocks in a page freed? +// are all blocks in a page freed? +// note: needs up-to-date used count, (as the `xthread_free` list may not be empty). see `_mi_page_collect_free`. static inline bool mi_page_all_free(const mi_page_t* page) { mi_assert_internal(page != NULL); return (page->used == 0); } -// are there immediately available blocks +// are there any available blocks? +static inline bool mi_page_has_any_available(const mi_page_t* page) { + mi_assert_internal(page != NULL && page->reserved > 0); + return (page->used < page->reserved || (mi_page_thread_free(page) != NULL)); +} + +// are there immediately available blocks, i.e. blocks available on the free list. static inline bool mi_page_immediate_available(const mi_page_t* page) { mi_assert_internal(page != NULL); return (page->free != NULL); } -// are there free blocks in this page? -static inline bool mi_page_has_free(mi_page_t* page) { - mi_assert_internal(page != NULL); - bool hasfree = (mi_page_immediate_available(page) || page->local_free != NULL || (mi_page_thread_free(page) != NULL)); - mi_assert_internal(hasfree || page->used == page->capacity); - return hasfree; -} - -// are all blocks in use? -static inline bool mi_page_all_used(mi_page_t* page) { - mi_assert_internal(page != NULL); - return !mi_page_has_free(page); -} // is more than 7/8th of a page in use? static inline bool mi_page_mostly_used(const mi_page_t* page) { diff --git a/src/page.c b/src/page.c index c5b86b0..e552a61 100644 --- a/src/page.c +++ b/src/page.c @@ -234,6 +234,7 @@ void _mi_page_reclaim(mi_heap_t* heap, mi_page_t* page) { mi_assert_internal(mi_page_thread_free_flag(page) != MI_NEVER_DELAYED_FREE); mi_assert_internal(_mi_page_segment(page)->page_kind != MI_PAGE_HUGE); mi_assert_internal(!page->is_reset); + // TODO: push on full queue immediately if it is full? mi_page_queue_t* pq = mi_page_queue(heap, mi_page_block_size(page)); mi_page_queue_push(heap, pq, page); mi_assert_expensive(_mi_page_is_valid(page)); @@ -245,28 +246,16 @@ static mi_page_t* mi_page_fresh_alloc(mi_heap_t* heap, mi_page_queue_t* pq, size mi_assert_internal(pq==NULL||block_size == pq->block_size); mi_page_t* page = _mi_segment_page_alloc(heap, block_size, &heap->tld->segments, &heap->tld->os); if (page == NULL) { - // this may be out-of-memory, or a page was reclaimed - if (pq!=NULL && (page = pq->first) != NULL) { - mi_assert_expensive(_mi_page_is_valid(page)); - if (!mi_page_immediate_available(page)) { - mi_page_extend_free(heap, page, heap->tld); - } - mi_assert_internal(mi_page_immediate_available(page)); - if (mi_page_immediate_available(page)) { - return page; // reclaimed page - } - } - return NULL; // out-of-memory - } - else { - // a fresh page was allocated, initialize it - mi_assert_internal(pq==NULL || _mi_page_segment(page)->page_kind != MI_PAGE_HUGE); - mi_page_init(heap, page, block_size, heap->tld); - _mi_stat_increase(&heap->tld->stats.pages, 1); - if (pq!=NULL) mi_page_queue_push(heap, pq, page); // huge pages use pq==NULL - mi_assert_expensive(_mi_page_is_valid(page)); - return page; + // this may be out-of-memory, or an abandoned page was reclaimed (and in our queue) + return NULL; } + // a fresh page was found, initialize it + mi_assert_internal(pq==NULL || _mi_page_segment(page)->page_kind != MI_PAGE_HUGE); + mi_page_init(heap, page, block_size, heap->tld); + _mi_stat_increase(&heap->tld->stats.pages, 1); + if (pq!=NULL) mi_page_queue_push(heap, pq, page); // huge pages use pq==NULL + mi_assert_expensive(_mi_page_is_valid(page)); + return page; } // Get a fresh page to use @@ -648,7 +637,7 @@ static void mi_page_init(mi_heap_t* heap, mi_page_t* page, size_t block_size, mi -------------------------------------------------------------*/ // Find a page with free blocks of `page->block_size`. -static mi_page_t* mi_page_queue_find_free_ex(mi_heap_t* heap, mi_page_queue_t* pq) +static mi_page_t* mi_page_queue_find_free_ex(mi_heap_t* heap, mi_page_queue_t* pq, bool first_try) { // search through the pages in "next fit" order size_t count = 0; @@ -686,13 +675,16 @@ static mi_page_t* mi_page_queue_find_free_ex(mi_heap_t* heap, mi_page_queue_t* p if (page == NULL) { _mi_heap_collect_retired(heap, false); // perhaps make a page available page = mi_page_fresh(heap, pq); + if (page == NULL && first_try) { + // out-of-memory _or_ an abandoned page with free blocks was reclaimed, try once again + page = mi_page_queue_find_free_ex(heap, pq, false); + } } else { mi_assert(pq->first == page); page->retire_expire = 0; } mi_assert_internal(page == NULL || mi_page_immediate_available(page)); - return page; } @@ -716,7 +708,7 @@ static inline mi_page_t* mi_find_free_page(mi_heap_t* heap, size_t size) { return page; // fast path } } - return mi_page_queue_find_free_ex(heap, pq); + return mi_page_queue_find_free_ex(heap, pq, true); } diff --git a/src/segment.c b/src/segment.c index 194aa79..c7a9662 100644 --- a/src/segment.c +++ b/src/segment.c @@ -669,6 +669,11 @@ static mi_segment_t* mi_segment_init(mi_segment_t* segment, size_t required, mi_ // set protection mi_segment_protect(segment, true, tld->os); + // insert in free lists for small and medium pages + if (page_kind <= MI_PAGE_MEDIUM) { + mi_segment_insert_in_free_queue(segment, tld); + } + //fprintf(stderr,"mimalloc: alloc segment at %p\n", (void*)segment); return segment; } @@ -1019,21 +1024,25 @@ void _mi_segment_page_abandon(mi_page_t* page, mi_segments_tld_t* tld) { ----------------------------------------------------------- */ // Possibly clear pages and check if free space is available -static bool mi_segment_check_free(mi_segment_t* segment, size_t block_size) +static bool mi_segment_check_free(mi_segment_t* segment, size_t block_size, bool* all_pages_free) { mi_assert_internal(block_size < MI_HUGE_BLOCK_SIZE); bool has_page = false; + size_t pages_used = 0; + size_t pages_used_empty = 0; for (size_t i = 0; i < segment->capacity; i++) { mi_page_t* page = &segment->pages[i]; if (page->segment_in_use) { + pages_used++; // ensure used count is up to date and collect potential concurrent frees _mi_page_free_collect(page, false); if (mi_page_all_free(page)) { // if everything free already, page can be reused for some block size - // note: don't clear yet as we can only reset it once it is reclaimed + // note: don't clear the page yet as we can only OS reset it once it is reclaimed + pages_used_empty++; has_page = true; } - else if (page->xblock_size == block_size && page->used < page->reserved) { + else if (page->xblock_size == block_size && mi_page_has_any_available(page)) { // a page has available free blocks of the right size has_page = true; } @@ -1043,15 +1052,19 @@ static bool mi_segment_check_free(mi_segment_t* segment, size_t block_size) has_page = true; } } + mi_assert_internal(pages_used == segment->used && pages_used >= pages_used_empty); + if (all_pages_free != NULL) { + *all_pages_free = ((pages_used - pages_used_empty) == 0); + } return has_page; } -#define MI_RECLAIMED ((mi_segment_t*)1) -// Reclaim a segment -static mi_segment_t* mi_segment_reclaim(mi_segment_t* segment, mi_heap_t* heap, size_t block_size, mi_segments_tld_t* tld) { +// Reclaim a segment; returns NULL if the segment was freed +// set `right_page_reclaimed` to `true` if it reclaimed a page of the right `block_size` that was not full. +static mi_segment_t* mi_segment_reclaim(mi_segment_t* segment, mi_heap_t* heap, size_t requested_block_size, bool* right_page_reclaimed, mi_segments_tld_t* tld) { mi_assert_internal(segment->abandoned_next == NULL); - bool right_page_reclaimed = false; + if (right_page_reclaimed != NULL) { *right_page_reclaimed = false; } segment->thread_id = _mi_thread_id(); segment->abandoned_visits = 0; @@ -1071,10 +1084,10 @@ static mi_segment_t* mi_segment_reclaim(mi_segment_t* segment, mi_heap_t* heap, segment->abandoned--; mi_assert(page->next == NULL); _mi_stat_decrease(&tld->stats->pages_abandoned, 1); - // set the heap again and allow delayed free again + // set the heap again and allow heap thread delayed free again. mi_page_set_heap(page, heap); _mi_page_use_delayed_free(page, MI_USE_DELAYED_FREE, true); // override never (after heap is set) - // TODO: should we not collect again given that we just collected? + // TODO: should we not collect again given that we just collected in `check_free`? _mi_page_free_collect(page, false); // ensure used count is up to date if (mi_page_all_free(page)) { // if everything free already, clear the page directly @@ -1083,77 +1096,67 @@ static mi_segment_t* mi_segment_reclaim(mi_segment_t* segment, mi_heap_t* heap, else { // otherwise reclaim it into the heap _mi_page_reclaim(heap, page); - if (block_size == page->xblock_size) { - right_page_reclaimed = true; + if (requested_block_size == page->xblock_size && mi_page_has_any_available(page)) { + if (right_page_reclaimed != NULL) { *right_page_reclaimed = true; } } } } else if (page->is_committed && !page->is_reset) { // not in-use, and not reset yet - // note: no not reset as this includes pages that were not touched before + // note: do not reset as this includes pages that were not touched before // mi_pages_reset_add(segment, page, tld); } } mi_assert_internal(segment->abandoned == 0); - if (right_page_reclaimed) { - // add the segment's free pages to the free small segment queue + if (segment->used == 0) { + mi_assert_internal(right_page_reclaimed == NULL || !(*right_page_reclaimed)); + mi_segment_free(segment, false, tld); + return NULL; + } + else { if (segment->page_kind <= MI_PAGE_MEDIUM && mi_segment_has_free(segment)) { mi_segment_insert_in_free_queue(segment, tld); } - // and return reclaimed: at the page allocation the page is already in the queue now - return MI_RECLAIMED; - } - else { - // otherwise return the segment as it will contain some free pages - // (except for abandoned_reclaim_all which uses a block_size of zero) - mi_assert_internal(segment->used < segment->capacity || block_size == 0); return segment; } } -// Reclaim a segment without returning it -static void mi_segment_reclaim_force(mi_segment_t* segment, mi_heap_t* heap, mi_segments_tld_t* tld) { - mi_segment_t* res = mi_segment_reclaim(segment, heap, 0, tld); - mi_assert_internal(res != MI_RECLAIMED); // due to block_size == 0 - if (res!=MI_RECLAIMED && res != NULL) { - mi_assert_internal(res == segment); - if (res->used == 0) { - mi_segment_free(segment, false, tld); - } - else if (res->page_kind <= MI_PAGE_MEDIUM && mi_segment_has_free(res)) { - mi_segment_insert_in_free_queue(res, tld); - } - } -} void _mi_abandoned_reclaim_all(mi_heap_t* heap, mi_segments_tld_t* tld) { mi_segment_t* segment; while ((segment = mi_abandoned_pop()) != NULL) { - mi_segment_reclaim_force(segment, heap, tld); + mi_segment_reclaim(segment, heap, 0, NULL, tld); } } - -static mi_segment_t* mi_segment_try_reclaim(mi_heap_t* heap, size_t block_size, mi_page_kind_t page_kind, mi_segments_tld_t* tld) +static mi_segment_t* mi_segment_try_reclaim(mi_heap_t* heap, size_t block_size, mi_page_kind_t page_kind, bool* reclaimed, mi_segments_tld_t* tld) { + *reclaimed = false; mi_segment_t* segment; int max_tries = 8; // limit the work to bound allocation times while ((max_tries-- > 0) && ((segment = mi_abandoned_pop()) != NULL)) { segment->abandoned_visits++; - bool has_page = mi_segment_check_free(segment,block_size); // try to free up pages (due to concurrent frees) - if (has_page && segment->page_kind == page_kind) { - // found a free page of the right kind, or page of the right block_size with free space - return mi_segment_reclaim(segment, heap, block_size, tld); + bool all_pages_free; + bool has_page = mi_segment_check_free(segment,block_size,&all_pages_free); // try to free up pages (due to concurrent frees) + if (all_pages_free) { + // 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 + // segment that is still partially used. + // note2: we could in principle optimize this by skipping reclaim and directly + // freeing but that would violate some invariants temporarily) + mi_segment_reclaim(segment, heap, 0, NULL, tld); } - else if (segment->used==0) { - // free the segment to make it available to other threads - mi_segment_os_free(segment, segment->segment_size, tld); + else if (has_page && segment->page_kind == page_kind) { + // found a free page of the right kind, or 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). + return mi_segment_reclaim(segment, heap, block_size, reclaimed, tld); } else if (segment->abandoned_visits >= 3) { - // always reclaim on 3rd visit to limit the list length - mi_segment_reclaim_force(segment, heap, tld); + // always reclaim on 3rd visit to limit the list length. + mi_segment_reclaim(segment, heap, 0, NULL, tld); } else { - // push on the visited list so it gets not looked at too quickly again + // otherwise, push on the visited list so it gets not looked at too quickly again mi_abandoned_visited_push(segment); } } @@ -1176,12 +1179,16 @@ static mi_segment_t* mi_segment_reclaim_or_alloc(mi_heap_t* heap, size_t block_s return segment; } // 2. try to reclaim an abandoned segment - segment = mi_segment_try_reclaim(heap, block_size, page_kind, tld); - if (segment == MI_RECLAIMED) { - return NULL; // pretend out-of-memory as the page will be in the page queue of the heap + bool reclaimed; + segment = mi_segment_try_reclaim(heap, block_size, page_kind, &reclaimed, tld); + if (reclaimed) { + // reclaimed the right page right into the heap + mi_assert_internal(segment != NULL && segment->page_kind == page_kind && page_kind <= MI_PAGE_LARGE); + return NULL; // pretend out-of-memory as the page will be in the page queue of the heap with available blocks } else if (segment != NULL) { - return segment; // reclaimed a segment with empty pages in it + // reclaimed a segment with empty pages (of `page_kind`) in it + return segment; } // 3. otherwise allocate a fresh segment return mi_segment_alloc(0, page_kind, page_shift, tld, os_tld); @@ -1216,12 +1223,12 @@ static mi_page_t* mi_segment_page_alloc(mi_heap_t* heap, size_t block_size, mi_p // find an available segment the segment free queue mi_segment_queue_t* const free_queue = mi_segment_free_queue_of_kind(kind, tld); if (mi_segment_queue_is_empty(free_queue)) { - // possibly allocate a fresh segment - mi_segment_t* segment = mi_segment_reclaim_or_alloc(heap, block_size, kind, page_shift, tld, os_tld); + // possibly allocate or reclaim a fresh segment + mi_segment_t* const segment = mi_segment_reclaim_or_alloc(heap, block_size, kind, page_shift, tld, os_tld); if (segment == NULL) return NULL; // return NULL if out-of-memory (or reclaimed) + mi_assert_internal(free_queue->first == segment); mi_assert_internal(segment->page_kind==kind); mi_assert_internal(segment->used < segment->capacity); - mi_segment_enqueue(free_queue, segment); } mi_assert_internal(free_queue->first != NULL); mi_page_t* const page = mi_segment_page_alloc_in(free_queue->first, tld);