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Diffstat (limited to 'src/segment-cache.c')
| -rw-r--r-- | src/segment-cache.c | 310 |
1 files changed, 310 insertions, 0 deletions
diff --git a/src/segment-cache.c b/src/segment-cache.c new file mode 100644 index 0000000..569e878 --- /dev/null +++ b/src/segment-cache.c @@ -0,0 +1,310 @@ +/* ---------------------------------------------------------------------------- +Copyright (c) 2020, Microsoft Research, Daan Leijen +This is free software; you can redistribute it and/or modify it under the +terms of the MIT license. A copy of the license can be found in the file +"LICENSE" at the root of this distribution. +-----------------------------------------------------------------------------*/ + +/* ---------------------------------------------------------------------------- + Implements a cache of segments to avoid expensive OS calls + and also the full memory map of all segments. +-----------------------------------------------------------------------------*/ +#include "mimalloc.h" +#include "mimalloc-internal.h" +#include "mimalloc-atomic.h" + +#include "bitmap.h" // atomic bitmap + +#define MI_CACHE_FIELDS (16) +#define MI_CACHE_MAX (MI_BITMAP_FIELD_BITS*MI_CACHE_FIELDS) // 1024 on 64-bit + +#define BITS_SET() ATOMIC_VAR_INIT(UINTPTR_MAX) +#define MI_CACHE_BITS_SET MI_INIT16(BITS_SET) + +typedef struct mi_cache_slot_s { + void* p; + size_t memid; + mi_commit_mask_t commit_mask; + _Atomic(mi_msecs_t) expire; +} mi_cache_slot_t; + +static mi_decl_cache_align mi_cache_slot_t cache[MI_CACHE_MAX]; // = 0 + +static mi_decl_cache_align mi_bitmap_field_t cache_available[MI_CACHE_FIELDS] = { MI_CACHE_BITS_SET }; // zero bit = available! +static mi_decl_cache_align mi_bitmap_field_t cache_available_large[MI_CACHE_FIELDS] = { MI_CACHE_BITS_SET }; +static mi_decl_cache_align mi_bitmap_field_t cache_inuse[MI_CACHE_FIELDS]; // zero bit = free + + +mi_decl_noinline void* _mi_segment_cache_pop(size_t size, mi_commit_mask_t* commit_mask, bool* large, bool* is_zero, size_t* memid, mi_os_tld_t* tld) +{ + // only segment blocks + if (size != MI_SEGMENT_SIZE) return NULL; + + // numa node determines start field + const int numa_node = _mi_os_numa_node(tld); + size_t start_field = 0; + if (numa_node > 0) { + start_field = (MI_CACHE_FIELDS / _mi_os_numa_node_count())*numa_node; + if (start_field >= MI_CACHE_FIELDS) start_field = 0; + } + + // find an available slot + mi_bitmap_index_t bitidx = 0; + bool claimed = false; + if (*large) { // large allowed? + claimed = _mi_bitmap_try_find_from_claim(cache_available_large, MI_CACHE_FIELDS, start_field, 1, &bitidx); + if (claimed) *large = true; + } + if (!claimed) { + claimed = _mi_bitmap_try_find_from_claim(cache_available, MI_CACHE_FIELDS, start_field, 1, &bitidx); + if (claimed) *large = false; + } + + if (!claimed) return NULL; + + // found a slot + mi_cache_slot_t* slot = &cache[mi_bitmap_index_bit(bitidx)]; + void* p = slot->p; + *memid = slot->memid; + *is_zero = false; + mi_commit_mask_t cmask = slot->commit_mask; // copy + slot->p = NULL; + mi_atomic_storei64_release(&slot->expire,(mi_msecs_t)0); + *commit_mask = cmask; + + // mark the slot as free again + mi_assert_internal(_mi_bitmap_is_claimed(cache_inuse, MI_CACHE_FIELDS, 1, bitidx)); + _mi_bitmap_unclaim(cache_inuse, MI_CACHE_FIELDS, 1, bitidx); + return p; +} + +static mi_decl_noinline void mi_commit_mask_decommit(mi_commit_mask_t* cmask, void* p, size_t total, mi_stats_t* stats) +{ + if (mi_commit_mask_is_empty(*cmask)) { + // nothing + } + else if (mi_commit_mask_is_full(*cmask)) { + _mi_os_decommit(p, total, stats); + } + else { + // todo: one call to decommit the whole at once? + mi_assert_internal((total%MI_COMMIT_MASK_BITS)==0); + size_t part = total/MI_COMMIT_MASK_BITS; + uintptr_t idx; + uintptr_t count; + mi_commit_mask_t mask = *cmask; + mi_commit_mask_foreach(mask, idx, count) { + void* start = (uint8_t*)p + (idx*part); + size_t size = count*part; + _mi_os_decommit(start, size, stats); + } + mi_commit_mask_foreach_end() + } + *cmask = mi_commit_mask_empty(); +} + +#define MI_MAX_PURGE_PER_PUSH (4) + +static mi_decl_noinline void mi_segment_cache_purge(mi_os_tld_t* tld) +{ + UNUSED(tld); + mi_msecs_t now = _mi_clock_now(); + size_t idx = (_mi_random_shuffle((uintptr_t)now) % MI_CACHE_MAX); // random start + size_t purged = 0; + for (size_t visited = 0; visited < MI_CACHE_FIELDS; visited++,idx++) { // probe just N slots + if (idx >= MI_CACHE_MAX) idx = 0; // wrap + mi_cache_slot_t* slot = &cache[idx]; + mi_msecs_t expire = mi_atomic_loadi64_relaxed(&slot->expire); + if (expire != 0 && now >= expire) { // racy read + // seems expired, first claim it from available + purged++; + mi_bitmap_index_t bitidx = mi_bitmap_index_create_from_bit(idx); + if (_mi_bitmap_claim(cache_available, MI_CACHE_FIELDS, 1, bitidx, NULL)) { + // was available, we claimed it + expire = mi_atomic_loadi64_acquire(&slot->expire); + if (expire != 0 && now >= expire) { // safe read + // still expired, decommit it + mi_atomic_storei64_relaxed(&slot->expire,(mi_msecs_t)0); + mi_assert_internal(!mi_commit_mask_is_empty(slot->commit_mask) && _mi_bitmap_is_claimed(cache_available_large, MI_CACHE_FIELDS, 1, bitidx)); + _mi_abandoned_await_readers(); // wait until safe to decommit + // decommit committed parts + // TODO: instead of decommit, we could also free to the OS? + mi_commit_mask_decommit(&slot->commit_mask, slot->p, MI_SEGMENT_SIZE, tld->stats); + } + _mi_bitmap_unclaim(cache_available, MI_CACHE_FIELDS, 1, bitidx); // make it available again for a pop + } + if (purged > MI_MAX_PURGE_PER_PUSH) break; // bound to no more than N purge tries per push + } + } +} + +mi_decl_noinline bool _mi_segment_cache_push(void* start, size_t size, size_t memid, mi_commit_mask_t commit_mask, bool is_large, mi_os_tld_t* tld) +{ + // only for normal segment blocks + if (size != MI_SEGMENT_SIZE || ((uintptr_t)start % MI_SEGMENT_ALIGN) != 0) return false; + + // numa node determines start field + int numa_node = _mi_os_numa_node(NULL); + size_t start_field = 0; + if (numa_node > 0) { + start_field = (MI_CACHE_FIELDS / _mi_os_numa_node_count())*numa_node; + if (start_field >= MI_CACHE_FIELDS) start_field = 0; + } + + // purge expired entries + mi_segment_cache_purge(tld); + + // find an available slot + mi_bitmap_index_t bitidx; + bool claimed = _mi_bitmap_try_find_from_claim(cache_inuse, MI_CACHE_FIELDS, start_field, 1, &bitidx); + if (!claimed) return false; + + mi_assert_internal(_mi_bitmap_is_claimed(cache_available, MI_CACHE_FIELDS, 1, bitidx)); + mi_assert_internal(_mi_bitmap_is_claimed(cache_available_large, MI_CACHE_FIELDS, 1, bitidx)); + + // set the slot + mi_cache_slot_t* slot = &cache[mi_bitmap_index_bit(bitidx)]; + slot->p = start; + slot->memid = memid; + mi_atomic_storei64_relaxed(&slot->expire,(mi_msecs_t)0); + slot->commit_mask = commit_mask; + if (!mi_commit_mask_is_empty(commit_mask) && !is_large) { + long delay = mi_option_get(mi_option_arena_reset_delay); + if (delay == 0) { + _mi_abandoned_await_readers(); // wait until safe to decommit + mi_commit_mask_decommit(&slot->commit_mask, start, MI_SEGMENT_SIZE, tld->stats); + } + else { + mi_atomic_storei64_release(&slot->expire, _mi_clock_now() + delay); + } + } + + // make it available + _mi_bitmap_unclaim((is_large ? cache_available_large : cache_available), MI_CACHE_FIELDS, 1, bitidx); + return true; +} + + +/* ----------------------------------------------------------- + The following functions are to reliably find the segment or + block that encompasses any pointer p (or NULL if it is not + in any of our segments). + We maintain a bitmap of all memory with 1 bit per MI_SEGMENT_SIZE (64MiB) + set to 1 if it contains the segment meta data. +----------------------------------------------------------- */ + + +#if (MI_INTPTR_SIZE==8) +#define MI_MAX_ADDRESS ((size_t)20 << 40) // 20TB +#else +#define MI_MAX_ADDRESS ((size_t)2 << 30) // 2Gb +#endif + +#define MI_SEGMENT_MAP_BITS (MI_MAX_ADDRESS / MI_SEGMENT_SIZE) +#define MI_SEGMENT_MAP_SIZE (MI_SEGMENT_MAP_BITS / 8) +#define MI_SEGMENT_MAP_WSIZE (MI_SEGMENT_MAP_SIZE / MI_INTPTR_SIZE) + +static _Atomic(uintptr_t)mi_segment_map[MI_SEGMENT_MAP_WSIZE]; // 2KiB per TB with 64MiB segments + +static size_t mi_segment_map_index_of(const mi_segment_t* segment, size_t* bitidx) { + mi_assert_internal(_mi_ptr_segment(segment) == segment); // is it aligned on MI_SEGMENT_SIZE? + uintptr_t segindex = ((uintptr_t)segment % MI_MAX_ADDRESS) / MI_SEGMENT_SIZE; + *bitidx = segindex % (8*MI_INTPTR_SIZE); + return (segindex / (8*MI_INTPTR_SIZE)); +} + +void _mi_segment_map_allocated_at(const mi_segment_t* segment) { + size_t bitidx; + size_t index = mi_segment_map_index_of(segment, &bitidx); + mi_assert_internal(index < MI_SEGMENT_MAP_WSIZE); + if (index==0) return; + uintptr_t mask = mi_atomic_load_relaxed(&mi_segment_map[index]); + uintptr_t newmask; + do { + newmask = (mask | ((uintptr_t)1 << bitidx)); + } while (!mi_atomic_cas_weak_release(&mi_segment_map[index], &mask, newmask)); +} + +void _mi_segment_map_freed_at(const mi_segment_t* segment) { + size_t bitidx; + size_t index = mi_segment_map_index_of(segment, &bitidx); + mi_assert_internal(index < MI_SEGMENT_MAP_WSIZE); + if (index == 0) return; + uintptr_t mask = mi_atomic_load_relaxed(&mi_segment_map[index]); + uintptr_t newmask; + do { + newmask = (mask & ~((uintptr_t)1 << bitidx)); + } while (!mi_atomic_cas_weak_release(&mi_segment_map[index], &mask, newmask)); +} + +// Determine the segment belonging to a pointer or NULL if it is not in a valid segment. +static mi_segment_t* _mi_segment_of(const void* p) { + mi_segment_t* segment = _mi_ptr_segment(p); + size_t bitidx; + size_t index = mi_segment_map_index_of(segment, &bitidx); + // fast path: for any pointer to valid small/medium/large object or first MI_SEGMENT_SIZE in huge + const uintptr_t mask = mi_atomic_load_relaxed(&mi_segment_map[index]); + if (mi_likely((mask & ((uintptr_t)1 << bitidx)) != 0)) { + return segment; // yes, allocated by us + } + if (index==0) return NULL; + // search downwards for the first segment in case it is an interior pointer + // could be slow but searches in MI_INTPTR_SIZE * MI_SEGMENT_SIZE (512MiB) steps trough + // valid huge objects + // note: we could maintain a lowest index to speed up the path for invalid pointers? + size_t lobitidx; + size_t loindex; + uintptr_t lobits = mask & (((uintptr_t)1 << bitidx) - 1); + if (lobits != 0) { + loindex = index; + lobitidx = mi_bsr(lobits); // lobits != 0 + } + else { + uintptr_t lomask = mask; + loindex = index - 1; + while (loindex > 0 && (lomask = mi_atomic_load_relaxed(&mi_segment_map[loindex])) == 0) loindex--; + if (loindex==0) return NULL; + lobitidx = mi_bsr(lomask); // lomask != 0 + } + // take difference as the addresses could be larger than the MAX_ADDRESS space. + size_t diff = (((index - loindex) * (8*MI_INTPTR_SIZE)) + bitidx - lobitidx) * MI_SEGMENT_SIZE; + segment = (mi_segment_t*)((uint8_t*)segment - diff); + + if (segment == NULL) return NULL; + mi_assert_internal((void*)segment < p); + bool cookie_ok = (_mi_ptr_cookie(segment) == segment->cookie); + mi_assert_internal(cookie_ok); + if (mi_unlikely(!cookie_ok)) return NULL; + if (((uint8_t*)segment + mi_segment_size(segment)) <= (uint8_t*)p) return NULL; // outside the range + mi_assert_internal(p >= (void*)segment && (uint8_t*)p < (uint8_t*)segment + mi_segment_size(segment)); + return segment; +} + +// Is this a valid pointer in our heap? +static bool mi_is_valid_pointer(const void* p) { + return (_mi_segment_of(p) != NULL); +} + +mi_decl_nodiscard mi_decl_export bool mi_is_in_heap_region(const void* p) mi_attr_noexcept { + return mi_is_valid_pointer(p); +} + +/* +// Return the full segment range belonging to a pointer +static void* mi_segment_range_of(const void* p, size_t* size) { + mi_segment_t* segment = _mi_segment_of(p); + if (segment == NULL) { + if (size != NULL) *size = 0; + return NULL; + } + else { + if (size != NULL) *size = segment->segment_size; + return segment; + } + mi_assert_expensive(page == NULL || mi_segment_is_valid(_mi_page_segment(page),tld)); + mi_assert_internal(page == NULL || (mi_segment_page_size(_mi_page_segment(page)) - (MI_SECURE == 0 ? 0 : _mi_os_page_size())) >= block_size); + mi_reset_delayed(tld); + mi_assert_internal(page == NULL || mi_page_not_in_queue(page, tld)); + return page; +} +*/ |