src/tcache.c

#include "jemalloc/internal/jemalloc_preamble.h"
#include "jemalloc/internal/jemalloc_internal_includes.h"

#include "jemalloc/internal/assert.h"
#include "jemalloc/internal/base.h"
#include "jemalloc/internal/mutex.h"
#include "jemalloc/internal/safety_check.h"
#include "jemalloc/internal/san.h"
#include "jemalloc/internal/sc.h"

/******************************************************************************/
/* Data. */

bool opt_tcache = true;

/* global_do_not_change_tcache_maxclass is set to 32KB by default. */
size_t opt_tcache_max = ((size_t)1) << 15;

/* Reasonable defaults for min and max values. */
unsigned opt_tcache_nslots_small_min = 20;
unsigned opt_tcache_nslots_small_max = 200;
unsigned opt_tcache_nslots_large = 20;

/*
 * We attempt to make the number of slots in a tcache bin for a given size class
 * equal to the number of objects in a slab times some multiplier.  By default,
 * the multiplier is 2 (i.e. we set the maximum number of objects in the tcache
 * to twice the number of objects in a slab).
 * This is bounded by some other constraints as well, like the fact that it
 * must be even, must be less than opt_tcache_nslots_small_max, etc..
 */
ssize_t	opt_lg_tcache_nslots_mul = 1;

/*
 * Number of allocation bytes between tcache incremental GCs.  Again, this
 * default just seems to work well; more tuning is possible.
 */
size_t opt_tcache_gc_incr_bytes = 65536;

/*
 * With default settings, we may end up flushing small bins frequently with
 * small flush amounts.  To limit this tendency, we can set a number of bytes to
 * "delay" by.  If we try to flush N M-byte items, we decrease that size-class's
 * delay by N * M.  So, if delay is 1024 and we're looking at the 64-byte size
 * class, we won't do any flushing until we've been asked to flush 1024/64 == 16
 * items.  This can happen in any configuration (i.e. being asked to flush 16
 * items once, or 4 items 4 times).
 *
 * Practically, this is stored as a count of items in a uint8_t, so the
 * effective maximum value for a size class is 255 * sz.
 */
size_t opt_tcache_gc_delay_bytes = 0;

/*
 * When a cache bin is flushed because it's full, how much of it do we flush?
 * By default, we flush half the maximum number of items.
 */
unsigned opt_lg_tcache_flush_small_div = 1;
unsigned opt_lg_tcache_flush_large_div = 1;

/*
 * Number of cache bins enabled, including both large and small.  This value
 * is only used to initialize tcache_nbins in the per-thread tcache.
 * Directly modifying it will not affect threads already launched.
 */
unsigned		global_do_not_change_tcache_nbins;
/*
 * Max size class to be cached (can be small or large). This value is only used
 * to initialize tcache_max in the per-thread tcache.   Directly modifying it
 * will not affect threads already launched.
 */
size_t			global_do_not_change_tcache_maxclass;

/*
 * Default bin info for each bin.  Will be initialized in malloc_conf_init
 * and tcache_boot and should not be modified after that.
 */
static cache_bin_info_t opt_tcache_ncached_max[TCACHE_NBINS_MAX] = {{0}};
/*
 * Marks whether a bin's info is set already.  This is used in
 * tcache_bin_info_compute to avoid overwriting ncached_max specified by
 * malloc_conf.  It should be set only when parsing malloc_conf.
 */
static bool opt_tcache_ncached_max_set[TCACHE_NBINS_MAX] = {0};

tcaches_t		*tcaches;

/* Index of first element within tcaches that has never been used. */
static unsigned		tcaches_past;

/* Head of singly linked list tracking available tcaches elements. */
static tcaches_t	*tcaches_avail;

/* Protects tcaches{,_past,_avail}. */
static malloc_mutex_t	tcaches_mtx;

/******************************************************************************/

size_t
tcache_salloc(tsdn_t *tsdn, const void *ptr) {
	return arena_salloc(tsdn, ptr);
}

uint64_t
tcache_gc_new_event_wait(tsd_t *tsd) {
	return opt_tcache_gc_incr_bytes;
}

uint64_t
tcache_gc_postponed_event_wait(tsd_t *tsd) {
	return TE_MIN_START_WAIT;
}

uint64_t
tcache_gc_dalloc_new_event_wait(tsd_t *tsd) {
	return opt_tcache_gc_incr_bytes;
}

uint64_t
tcache_gc_dalloc_postponed_event_wait(tsd_t *tsd) {
	return TE_MIN_START_WAIT;
}

static uint8_t
tcache_gc_item_delay_compute(szind_t szind) {
	assert(szind < SC_NBINS);
	size_t sz = sz_index2size(szind);
	size_t item_delay = opt_tcache_gc_delay_bytes / sz;
	size_t delay_max = ZU(1)
	    << (sizeof(((tcache_slow_t *)NULL)->bin_flush_delay_items[0]) * 8);
	if (item_delay >= delay_max) {
		item_delay = delay_max - 1;
	}
	return (uint8_t)item_delay;
}

static void
tcache_gc_small(tsd_t *tsd, tcache_slow_t *tcache_slow, tcache_t *tcache,
    szind_t szind) {
	/* Aim to flush 3/4 of items below low-water. */
	assert(szind < SC_NBINS);

	cache_bin_t *cache_bin = &tcache->bins[szind];
	assert(!tcache_bin_disabled(szind, cache_bin, tcache->tcache_slow));
	cache_bin_sz_t ncached = cache_bin_ncached_get_local(cache_bin);
	cache_bin_sz_t low_water = cache_bin_low_water_get(cache_bin);
	assert(!tcache_slow->bin_refilled[szind]);

	size_t nflush = low_water - (low_water >> 2);
	if (nflush < tcache_slow->bin_flush_delay_items[szind]) {
		/* Workaround for a conversion warning. */
		uint8_t nflush_uint8 = (uint8_t)nflush;
		assert(sizeof(tcache_slow->bin_flush_delay_items[0]) ==
		    sizeof(nflush_uint8));
		tcache_slow->bin_flush_delay_items[szind] -= nflush_uint8;
		return;
	}

	tcache_slow->bin_flush_delay_items[szind]
	    = tcache_gc_item_delay_compute(szind);
	tcache_bin_flush_small(tsd, tcache, cache_bin, szind,
	    (unsigned)(ncached - nflush));

	/*
	 * Reduce fill count by 2X.  Limit lg_fill_div such that
	 * the fill count is always at least 1.
	 */
	if ((cache_bin_ncached_max_get(cache_bin) >>
	    (tcache_slow->lg_fill_div[szind] + 1)) >= 1) {
		tcache_slow->lg_fill_div[szind]++;
	}
}

static void
tcache_gc_large(tsd_t *tsd, tcache_slow_t *tcache_slow, tcache_t *tcache,
    szind_t szind) {
	/* Like the small GC; flush 3/4 of untouched items. */
	assert(szind >= SC_NBINS);
	cache_bin_t *cache_bin = &tcache->bins[szind];
	assert(!tcache_bin_disabled(szind, cache_bin, tcache->tcache_slow));
	cache_bin_sz_t ncached = cache_bin_ncached_get_local(cache_bin);
	cache_bin_sz_t low_water = cache_bin_low_water_get(cache_bin);
	tcache_bin_flush_large(tsd, tcache, cache_bin, szind,
	    (unsigned)(ncached - low_water + (low_water >> 2)));
}

static void
tcache_event(tsd_t *tsd) {
	tcache_t *tcache = tcache_get(tsd);
	if (tcache == NULL) {
		return;
	}

	tcache_slow_t *tcache_slow = tsd_tcache_slowp_get(tsd);
	szind_t szind = tcache_slow->next_gc_bin;
	bool is_small = (szind < SC_NBINS);
	cache_bin_t *cache_bin = &tcache->bins[szind];

	if (tcache_bin_disabled(szind, cache_bin, tcache_slow)) {
		goto label_done;
	}

	tcache_bin_flush_stashed(tsd, tcache, cache_bin, szind, is_small);
	cache_bin_sz_t low_water = cache_bin_low_water_get(cache_bin);
	if (low_water > 0) {
		if (is_small) {
			tcache_gc_small(tsd, tcache_slow, tcache, szind);
		} else {
			tcache_gc_large(tsd, tcache_slow, tcache, szind);
		}
	} else if (is_small && tcache_slow->bin_refilled[szind]) {
		assert(low_water == 0);
		/*
		 * Increase fill count by 2X for small bins.  Make sure
		 * lg_fill_div stays greater than 0.
		 */
		if (tcache_slow->lg_fill_div[szind] > 1) {
			tcache_slow->lg_fill_div[szind]--;
		}
		tcache_slow->bin_refilled[szind] = false;
	}
	cache_bin_low_water_set(cache_bin);

label_done:
	tcache_slow->next_gc_bin++;
	if (tcache_slow->next_gc_bin == tcache_nbins_get(tcache_slow)) {
		tcache_slow->next_gc_bin = 0;
	}
}

void
tcache_gc_event_handler(tsd_t *tsd, uint64_t elapsed) {
	assert(elapsed == TE_INVALID_ELAPSED);
	tcache_event(tsd);
}

void
tcache_gc_dalloc_event_handler(tsd_t *tsd, uint64_t elapsed) {
	assert(elapsed == TE_INVALID_ELAPSED);
	tcache_event(tsd);
}

void *
tcache_alloc_small_hard(tsdn_t *tsdn, arena_t *arena,
    tcache_t *tcache, cache_bin_t *cache_bin, szind_t binind,
    bool *tcache_success) {
	tcache_slow_t *tcache_slow = tcache->tcache_slow;
	void *ret;

	assert(tcache_slow->arena != NULL);
	assert(!tcache_bin_disabled(binind, cache_bin, tcache_slow));
	cache_bin_sz_t nfill = cache_bin_ncached_max_get(cache_bin)
	    >> tcache_slow->lg_fill_div[binind];
	if (nfill == 0) {
		nfill = 1;
	}
	arena_cache_bin_fill_small(tsdn, arena, cache_bin, binind, nfill);
	tcache_slow->bin_refilled[binind] = true;
	ret = cache_bin_alloc(cache_bin, tcache_success);

	return ret;
}

static const void *
tcache_bin_flush_ptr_getter(void *arr_ctx, size_t ind) {
	cache_bin_ptr_array_t *arr = (cache_bin_ptr_array_t *)arr_ctx;
	return arr->ptr[ind];
}

static void
tcache_bin_flush_metadata_visitor(void *szind_sum_ctx,
    emap_full_alloc_ctx_t *alloc_ctx) {
	size_t *szind_sum = (size_t *)szind_sum_ctx;
	*szind_sum -= alloc_ctx->szind;
	util_prefetch_write_range(alloc_ctx->edata, sizeof(edata_t));
}

JEMALLOC_NOINLINE static void
tcache_bin_flush_size_check_fail(cache_bin_ptr_array_t *arr, szind_t szind,
    size_t nptrs, emap_batch_lookup_result_t *edatas) {
	bool found_mismatch = false;
	for (size_t i = 0; i < nptrs; i++) {
		szind_t true_szind = edata_szind_get(edatas[i].edata);
		if (true_szind != szind) {
			found_mismatch = true;
			safety_check_fail_sized_dealloc(
			    /* current_dealloc */ false,
			    /* ptr */ tcache_bin_flush_ptr_getter(arr, i),
			    /* true_size */ sz_index2size(true_szind),
			    /* input_size */ sz_index2size(szind));
		}
	}
	assert(found_mismatch);
}

static void
tcache_bin_flush_edatas_lookup(tsd_t *tsd, cache_bin_ptr_array_t *arr,
    szind_t binind, size_t nflush, emap_batch_lookup_result_t *edatas) {

	/*
	 * This gets compiled away when config_opt_safety_checks is false.
	 * Checks for sized deallocation bugs, failing early rather than
	 * corrupting metadata.
	 */
	size_t szind_sum = binind * nflush;
	emap_edata_lookup_batch(tsd, &arena_emap_global, nflush,
	    &tcache_bin_flush_ptr_getter, (void *)arr,
	    &tcache_bin_flush_metadata_visitor, (void *)&szind_sum,
	    edatas);
	if (config_opt_safety_checks && unlikely(szind_sum != 0)) {
		tcache_bin_flush_size_check_fail(arr, binind, nflush, edatas);
	}
}

JEMALLOC_ALWAYS_INLINE void
tcache_bin_flush_impl_small(tsd_t *tsd, tcache_t *tcache, cache_bin_t *cache_bin,
    szind_t binind, cache_bin_ptr_array_t *ptrs, unsigned nflush) {
	tcache_slow_t *tcache_slow = tcache->tcache_slow;
	/*
	 * A couple lookup calls take tsdn; declare it once for convenience
	 * instead of calling tsd_tsdn(tsd) all the time.
	 */
	tsdn_t *tsdn = tsd_tsdn(tsd);

	assert(binind < SC_NBINS);
	arena_t *tcache_arena = tcache_slow->arena;
	assert(tcache_arena != NULL);
	unsigned tcache_binshard = tsd_binshardsp_get(tsdn_tsd(tsdn))->binshard[binind];

	/*
	 * Variable length array must have > 0 length; the last element is never
	 * touched (it's just included to satisfy the no-zero-length rule).
	 */
	VARIABLE_ARRAY(emap_batch_lookup_result_t, item_edata, nflush + 1);
	tcache_bin_flush_edatas_lookup(tsd, ptrs, binind, nflush, item_edata);

	/*
	 * The slabs where we freed the last remaining object in the slab (and
	 * so need to free the slab itself).
	 * Used only if small == true.
	 */
	unsigned dalloc_count = 0;
	VARIABLE_ARRAY(edata_t *, dalloc_slabs, nflush + 1);

	/*
	 * There's an edge case where we need to deallocate more slabs than we
	 * have elements of dalloc_slabs.  This can if we end up deallocating
	 * items batched by another thread in addition to ones flushed from the
	 * cache.  Since this is not very likely (most small object
	 * deallocations don't free up a whole slab), we don't want to burn the
	 * stack space to keep those excess slabs in an array.  Instead we'll
	 * maintain an overflow list.
	 */
	edata_list_active_t dalloc_slabs_extra;
	edata_list_active_init(&dalloc_slabs_extra);

	/*
	 * We're about to grab a bunch of locks.  If one of them happens to be
	 * the one guarding the arena-level stats counters we flush our
	 * thread-local ones to, we do so under one critical section.
	 */
	bool merged_stats = false;

	/*
	 * We maintain the invariant that all edatas yet to be flushed are
	 * contained in the half-open range [flush_start, flush_end).  We'll
	 * repeatedly partition the array so that the unflushed items are at the
	 * end.
	 */
	unsigned flush_start = 0;

	while (flush_start < nflush) {
		/*
		 * After our partitioning step, all objects to flush will be in
		 * the half-open range [prev_flush_start, flush_start), and
		 * flush_start will be updated to correspond to the next loop
		 * iteration.
		 */
		unsigned prev_flush_start = flush_start;

		edata_t *cur_edata = item_edata[flush_start].edata;
		unsigned cur_arena_ind = edata_arena_ind_get(cur_edata);
		arena_t *cur_arena = arena_get(tsdn, cur_arena_ind, false);

		unsigned cur_binshard = edata_binshard_get(cur_edata);
		bin_t *cur_bin = arena_get_bin(cur_arena, binind,
		    cur_binshard);
		assert(cur_binshard < bin_infos[binind].n_shards);

		/*
		 * Start off the partition; item_edata[i] always matches itself
		 * of course.
		 */
		flush_start++;
		for (unsigned i = flush_start; i < nflush; i++) {
			void *ptr = ptrs->ptr[i];
			edata_t *edata = item_edata[i].edata;
			assert(ptr != NULL && edata != NULL);
			assert((uintptr_t)ptr >= (uintptr_t)edata_addr_get(edata));
			assert((uintptr_t)ptr < (uintptr_t)edata_past_get(edata));
			if (edata_arena_ind_get(edata) == cur_arena_ind
			    && edata_binshard_get(edata) == cur_binshard) {
				/* Swap the edatas. */
				emap_batch_lookup_result_t temp_edata
				    = item_edata[flush_start];
				item_edata[flush_start] = item_edata[i];
				item_edata[i] = temp_edata;
				/* Swap the pointers */
				void *temp_ptr = ptrs->ptr[flush_start];
				ptrs->ptr[flush_start] = ptrs->ptr[i];
				ptrs->ptr[i] = temp_ptr;
				flush_start++;
			}
		}
		/* Make sure we implemented partitioning correctly. */
		if (config_debug) {
			for (unsigned i = prev_flush_start; i < flush_start;
			    i++) {
				edata_t *edata = item_edata[i].edata;
				unsigned arena_ind = edata_arena_ind_get(edata);
				assert(arena_ind == cur_arena_ind);
				unsigned binshard = edata_binshard_get(edata);
				assert(binshard == cur_binshard);
			}
			for (unsigned i = flush_start; i < nflush; i++) {
				edata_t *edata = item_edata[i].edata;
				assert(edata_arena_ind_get(edata)
				    != cur_arena_ind
				    || edata_binshard_get(edata)
				    != cur_binshard);
			}
		}

		/*
		 * We never batch when flushing to our home-base bin shard,
		 * since it's likely that we'll have to acquire that lock anyway
		 * when flushing stats.
		 *
		 * A plausible check we could add to can_batch is
		 * '&& arena_is_auto(cur_arena)'.  The motivation would be that
		 * we have a higher tolerance for dubious user assumptions
		 * around non-auto arenas (e.g. "if I deallocate every object I
		 * allocated, and then call tcache.flush, then the arena stats
		 * must reflect zero live allocations").
		 *
		 * This is dubious for a couple reasons:
		 * - We already don't provide perfect fidelity for stats
		 *   counting (e.g. for profiled allocations, whose size can
		 *   inflate in stats).
		 * - Hanging load-bearing guarantees around stats impedes
		 *   scalability in general.
		 *
		 * There are some "complete" strategies we could do instead:
		 * - Add a arena.<i>.quiesce call to pop all bins for users who
		 *   do want those stats accounted for.
		 * - Make batchability a user-controllable per-arena option.
		 * - Do a batch pop after every mutex acquisition for which we
		 *   want to provide accurate stats.  This gives perfectly
		 *   accurate stats, but can cause weird performance effects
		 *   (because doing stats collection can now result in slabs
		 *   becoming empty, and therefore purging, large mutex
		 *   acquisition, etc.).
		 * - Propagate the "why" behind a flush down to the level of the
		 *   batcher, and include a batch pop attempt down full tcache
		 *   flushing pathways.  This is just a lot of plumbing and
		 *   internal complexity.
		 *
		 * We don't do any of these right now, but the decision calculus
		 * and tradeoffs are subtle enough that the reasoning was worth
		 * leaving in this comment.
		 */
		bool bin_is_batched = arena_bin_has_batch(binind);
		bool home_binshard = (cur_arena == tcache_arena
		    && cur_binshard == tcache_binshard);
		bool can_batch = (flush_start - prev_flush_start
		    <= opt_bin_info_remote_free_max_batch)
		    && !home_binshard && bin_is_batched;

		/*
		 * We try to avoid the batching pathway if we can, so we always
		 * at least *try* to lock.
		 */
		bool locked = false;
		bool batched = false;
		bool batch_failed = false;
		if (can_batch) {
			locked = !malloc_mutex_trylock(tsdn, &cur_bin->lock);
		}
		if (can_batch && !locked) {
			bin_with_batch_t *batched_bin =
			    (bin_with_batch_t *)cur_bin;
			size_t push_idx = batcher_push_begin(tsdn,
			    &batched_bin->remote_frees,
			    flush_start - prev_flush_start);
			bin_batching_test_after_push(push_idx);

			if (push_idx != BATCHER_NO_IDX) {
				batched = true;
				unsigned nbatched
				    = flush_start - prev_flush_start;
				for (unsigned i = 0; i < nbatched; i++) {
					unsigned src_ind = prev_flush_start + i;
					batched_bin->remote_free_data[
					    push_idx + i].ptr
						= ptrs->ptr[src_ind];
					batched_bin->remote_free_data[
					    push_idx + i].slab
						= item_edata[src_ind].edata;
				}
				batcher_push_end(tsdn,
				    &batched_bin->remote_frees);
			} else {
				batch_failed = true;
			}
		}
		if (!batched) {
			if (!locked) {
				malloc_mutex_lock(tsdn, &cur_bin->lock);
			}
			/*
			 * Unlike other stats (which only ever get flushed into
			 * a tcache's associated arena), batch_failed counts get
			 * accumulated into the bin where the push attempt
			 * failed.
			 */
			if (config_stats && batch_failed) {
				cur_bin->stats.batch_failed_pushes++;
			}

			/*
			 * Flush stats first, if that was the right lock.  Note
			 * that we don't actually have to flush stats into the
			 * current thread's binshard. Flushing into any binshard
			 * in the same arena is enough; we don't expose stats on
			 * per-binshard basis (just per-bin).
			 */
			if (config_stats && tcache_arena == cur_arena
			    && !merged_stats) {
				merged_stats = true;
				cur_bin->stats.nflushes++;
				cur_bin->stats.nrequests +=
				    cache_bin->tstats.nrequests;
				cache_bin->tstats.nrequests = 0;
			}
			unsigned preallocated_slabs = nflush;
			unsigned ndalloc_slabs = arena_bin_batch_get_ndalloc_slabs(
			    preallocated_slabs);

			/* Next flush objects our own objects. */
			/* Init only to avoid used-uninitialized warning. */
			arena_dalloc_bin_locked_info_t dalloc_bin_info = {0};
			arena_dalloc_bin_locked_begin(&dalloc_bin_info, binind);
			for (unsigned i = prev_flush_start; i < flush_start;
			    i++) {
				void *ptr = ptrs->ptr[i];
				edata_t *edata = item_edata[i].edata;
				arena_dalloc_bin_locked_step(tsdn, cur_arena,
				    cur_bin, &dalloc_bin_info, binind, edata,
				    ptr, dalloc_slabs, ndalloc_slabs,
				    &dalloc_count, &dalloc_slabs_extra);
			}
			/*
			 * Lastly, flush any batched objects (from other
			 * threads).
			 */
			if (bin_is_batched) {
				arena_bin_flush_batch_impl(tsdn, cur_arena,
				    cur_bin, &dalloc_bin_info, binind,
				    dalloc_slabs, ndalloc_slabs,
				    &dalloc_count, &dalloc_slabs_extra);
			}

			arena_dalloc_bin_locked_finish(tsdn, cur_arena, cur_bin,
			    &dalloc_bin_info);
			malloc_mutex_unlock(tsdn, &cur_bin->lock);
		}
		arena_decay_ticks(tsdn, cur_arena,
		    flush_start - prev_flush_start);
	}

	/* Handle all deferred slab dalloc. */
	for (unsigned i = 0; i < dalloc_count; i++) {
		edata_t *slab = dalloc_slabs[i];
		arena_slab_dalloc(tsdn, arena_get_from_edata(slab), slab);
	}
	while (!edata_list_active_empty(&dalloc_slabs_extra)) {
		edata_t *slab = edata_list_active_first(&dalloc_slabs_extra);
		edata_list_active_remove(&dalloc_slabs_extra, slab);
		arena_slab_dalloc(tsdn, arena_get_from_edata(slab), slab);
	}

	if (config_stats && !merged_stats) {
			/*
			 * The flush loop didn't happen to flush to this
			 * thread's arena, so the stats didn't get merged.
			 * Manually do so now.
			 */
			bin_t *bin = arena_bin_choose(tsdn, tcache_arena,
			    binind, NULL);
			malloc_mutex_lock(tsdn, &bin->lock);
			bin->stats.nflushes++;
			bin->stats.nrequests += cache_bin->tstats.nrequests;
			cache_bin->tstats.nrequests = 0;
			malloc_mutex_unlock(tsdn, &bin->lock);
	}
}

JEMALLOC_ALWAYS_INLINE void
tcache_bin_flush_impl_large(tsd_t *tsd, tcache_t *tcache, cache_bin_t *cache_bin,
    szind_t binind, cache_bin_ptr_array_t *ptrs, unsigned nflush) {
	tcache_slow_t *tcache_slow = tcache->tcache_slow;
	/*
	 * A couple lookup calls take tsdn; declare it once for convenience
	 * instead of calling tsd_tsdn(tsd) all the time.
	 */
	tsdn_t *tsdn = tsd_tsdn(tsd);

	assert(binind < tcache_nbins_get(tcache_slow));
	arena_t *tcache_arena = tcache_slow->arena;
	assert(tcache_arena != NULL);

	/*
	 * Variable length array must have > 0 length; the last element is never
	 * touched (it's just included to satisfy the no-zero-length rule).
	 */
	VARIABLE_ARRAY(emap_batch_lookup_result_t, item_edata, nflush + 1);
	tcache_bin_flush_edatas_lookup(tsd, ptrs, binind, nflush, item_edata);

	/*
	 * We're about to grab a bunch of locks.  If one of them happens to be
	 * the one guarding the arena-level stats counters we flush our
	 * thread-local ones to, we do so under one critical section.
	 */
	bool merged_stats = false;
	while (nflush > 0) {
		/* Lock the arena, or bin, associated with the first object. */
		edata_t *edata = item_edata[0].edata;
		unsigned cur_arena_ind = edata_arena_ind_get(edata);
		arena_t *cur_arena = arena_get(tsdn, cur_arena_ind, false);

		if (!arena_is_auto(cur_arena)) {
			malloc_mutex_lock(tsdn, &cur_arena->large_mtx);
		}

		/*
		 * If we acquired the right lock and have some stats to flush,
		 * flush them.
		 */
		if (config_stats && tcache_arena == cur_arena
		    && !merged_stats) {
			merged_stats = true;
			arena_stats_large_flush_nrequests_add(tsdn,
			    &tcache_arena->stats, binind,
			    cache_bin->tstats.nrequests);
			cache_bin->tstats.nrequests = 0;
		}

		/*
		 * Large allocations need special prep done.  Afterwards, we can
		 * drop the large lock.
		 */
		for (unsigned i = 0; i < nflush; i++) {
			void *ptr = ptrs->ptr[i];
			edata = item_edata[i].edata;
			assert(ptr != NULL && edata != NULL);

			if (edata_arena_ind_get(edata) == cur_arena_ind) {
				large_dalloc_prep_locked(tsdn,
				    edata);
			}
		}
		if (!arena_is_auto(cur_arena)) {
			malloc_mutex_unlock(tsdn, &cur_arena->large_mtx);
		}

		/* Deallocate whatever we can. */
		unsigned ndeferred = 0;
		for (unsigned i = 0; i < nflush; i++) {
			void *ptr = ptrs->ptr[i];
			edata = item_edata[i].edata;
			assert(ptr != NULL && edata != NULL);
			if (edata_arena_ind_get(edata) != cur_arena_ind) {
				/*
				 * The object was allocated either via a
				 * different arena, or a different bin in this
				 * arena.  Either way, stash the object so that
				 * it can be handled in a future pass.
				 */
				ptrs->ptr[ndeferred] = ptr;
				item_edata[ndeferred].edata = edata;
				ndeferred++;
				continue;
			}
			if (large_dalloc_safety_checks(edata, ptr, binind)) {
				/* See the comment in isfree. */
				continue;
			}
			large_dalloc_finish(tsdn, edata);
		}
		arena_decay_ticks(tsdn, cur_arena, nflush - ndeferred);
		nflush = ndeferred;
	}

	if (config_stats && !merged_stats) {
		arena_stats_large_flush_nrequests_add(tsdn,
		    &tcache_arena->stats, binind,
		    cache_bin->tstats.nrequests);
		cache_bin->tstats.nrequests = 0;
	}
}

JEMALLOC_ALWAYS_INLINE void
tcache_bin_flush_impl(tsd_t *tsd, tcache_t *tcache, cache_bin_t *cache_bin,
    szind_t binind, cache_bin_ptr_array_t *ptrs, unsigned nflush, bool small) {
	/*
	 * The small/large flush logic is very similar; you might conclude that
	 * it's a good opportunity to share code.  We've tried this, and by and
	 * large found this to obscure more than it helps; there are so many
	 * fiddly bits around things like stats handling, precisely when and
	 * which mutexes are acquired, etc., that almost all code ends up being
	 * gated behind 'if (small) { ... } else { ... }'.  Even though the
	 * '...' is morally equivalent, the code itself needs slight tweaks.
	 */
	if (small) {
		tcache_bin_flush_impl_small(tsd, tcache, cache_bin, binind,
		    ptrs, nflush);
	} else {
		tcache_bin_flush_impl_large(tsd, tcache, cache_bin, binind,
		    ptrs, nflush);
	}
}

JEMALLOC_ALWAYS_INLINE void
tcache_bin_flush_bottom(tsd_t *tsd, tcache_t *tcache, cache_bin_t *cache_bin,
    szind_t binind, unsigned rem, bool small) {
	assert(rem <= cache_bin_ncached_max_get(cache_bin));
	assert(!tcache_bin_disabled(binind, cache_bin, tcache->tcache_slow));
	cache_bin_sz_t orig_nstashed = cache_bin_nstashed_get_local(cache_bin);
	tcache_bin_flush_stashed(tsd, tcache, cache_bin, binind, small);

	cache_bin_sz_t ncached = cache_bin_ncached_get_local(cache_bin);
	assert((cache_bin_sz_t)rem <= ncached + orig_nstashed);
	if ((cache_bin_sz_t)rem > ncached) {
		/*
		 * The flush_stashed above could have done enough flushing, if
		 * there were many items stashed.  Validate that: 1) non zero
		 * stashed, and 2) bin stack has available space now.
		 */
		assert(orig_nstashed > 0);
		assert(ncached + cache_bin_nstashed_get_local(cache_bin)
		    < cache_bin_ncached_max_get(cache_bin));
		/* Still go through the flush logic for stats purpose only. */
		rem = ncached;
	}
	cache_bin_sz_t nflush = ncached - (cache_bin_sz_t)rem;

	CACHE_BIN_PTR_ARRAY_DECLARE(ptrs, nflush);
	cache_bin_init_ptr_array_for_flush(cache_bin, &ptrs, nflush);

	tcache_bin_flush_impl(tsd, tcache, cache_bin, binind, &ptrs, nflush,
	    small);

	cache_bin_finish_flush(cache_bin, &ptrs, nflush);
}

void
tcache_bin_flush_small(tsd_t *tsd, tcache_t *tcache, cache_bin_t *cache_bin,
    szind_t binind, unsigned rem) {
	tcache_bin_flush_bottom(tsd, tcache, cache_bin, binind, rem,
	    /* small */ true);
}

void
tcache_bin_flush_large(tsd_t *tsd, tcache_t *tcache, cache_bin_t *cache_bin,
    szind_t binind, unsigned rem) {
	tcache_bin_flush_bottom(tsd, tcache, cache_bin, binind, rem,
	    /* small */ false);
}

/*
 * Flushing stashed happens when 1) tcache fill, 2) tcache flush, or 3) tcache
 * GC event.  This makes sure that the stashed items do not hold memory for too
 * long, and new buffers can only be allocated when nothing is stashed.
 *
 * The downside is, the time between stash and flush may be relatively short,
 * especially when the request rate is high.  It lowers the chance of detecting
 * write-after-free -- however that is a delayed detection anyway, and is less
 * of a focus than the memory overhead.
 */
void
tcache_bin_flush_stashed(tsd_t *tsd, tcache_t *tcache, cache_bin_t *cache_bin,
    szind_t binind, bool is_small) {
	assert(!tcache_bin_disabled(binind, cache_bin, tcache->tcache_slow));
	/*
	 * The two below are for assertion only.  The content of original cached
	 * items remain unchanged -- the stashed items reside on the other end
	 * of the stack.  Checking the stack head and ncached to verify.
	 */
	void *head_content = *cache_bin->stack_head;
	cache_bin_sz_t orig_cached = cache_bin_ncached_get_local(cache_bin);

	cache_bin_sz_t nstashed = cache_bin_nstashed_get_local(cache_bin);
	assert(orig_cached + nstashed <= cache_bin_ncached_max_get(cache_bin));
	if (nstashed == 0) {
		return;
	}

	CACHE_BIN_PTR_ARRAY_DECLARE(ptrs, nstashed);
	cache_bin_init_ptr_array_for_stashed(cache_bin, binind, &ptrs,
	    nstashed);
	san_check_stashed_ptrs(ptrs.ptr, nstashed, sz_index2size(binind));
	tcache_bin_flush_impl(tsd, tcache, cache_bin, binind, &ptrs, nstashed,
	    is_small);
	cache_bin_finish_flush_stashed(cache_bin);

	assert(cache_bin_nstashed_get_local(cache_bin) == 0);
	assert(cache_bin_ncached_get_local(cache_bin) == orig_cached);
	assert(head_content == *cache_bin->stack_head);
}

JET_EXTERN bool
tcache_get_default_ncached_max_set(szind_t ind) {
	return opt_tcache_ncached_max_set[ind];
}

JET_EXTERN const cache_bin_info_t *
tcache_get_default_ncached_max(void) {
	return opt_tcache_ncached_max;
}

bool
tcache_bin_ncached_max_read(tsd_t *tsd, size_t bin_size,
    cache_bin_sz_t *ncached_max) {
	if (bin_size > TCACHE_MAXCLASS_LIMIT) {
		return true;
	}

	if (!tcache_available(tsd)) {
		*ncached_max = 0;
		return false;
	}

	tcache_t *tcache = tsd_tcachep_get(tsd);
	assert(tcache != NULL);
	szind_t bin_ind = sz_size2index(bin_size);

	cache_bin_t *bin = &tcache->bins[bin_ind];
	*ncached_max = tcache_bin_disabled(bin_ind, bin, tcache->tcache_slow) ?
	    0: cache_bin_ncached_max_get(bin);
	return false;
}

void
tcache_arena_associate(tsdn_t *tsdn, tcache_slow_t *tcache_slow,
    tcache_t *tcache, arena_t *arena) {
	assert(tcache_slow->arena == NULL);
	tcache_slow->arena = arena;

	if (config_stats) {
		/* Link into list of extant tcaches. */
		malloc_mutex_lock(tsdn, &arena->tcache_ql_mtx);

		ql_elm_new(tcache_slow, link);
		ql_tail_insert(&arena->tcache_ql, tcache_slow, link);
		cache_bin_array_descriptor_init(
		    &tcache_slow->cache_bin_array_descriptor, tcache->bins);
		ql_tail_insert(&arena->cache_bin_array_descriptor_ql,
		    &tcache_slow->cache_bin_array_descriptor, link);

		malloc_mutex_unlock(tsdn, &arena->tcache_ql_mtx);
	}
}

static void
tcache_arena_dissociate(tsdn_t *tsdn, tcache_slow_t *tcache_slow,
    tcache_t *tcache) {
	arena_t *arena = tcache_slow->arena;
	assert(arena != NULL);
	if (config_stats) {
		/* Unlink from list of extant tcaches. */
		malloc_mutex_lock(tsdn, &arena->tcache_ql_mtx);
		if (config_debug) {
			bool in_ql = false;
			tcache_slow_t *iter;
			ql_foreach(iter, &arena->tcache_ql, link) {
				if (iter == tcache_slow) {
					in_ql = true;
					break;
				}
			}
			assert(in_ql);
		}
		ql_remove(&arena->tcache_ql, tcache_slow, link);
		ql_remove(&arena->cache_bin_array_descriptor_ql,
		    &tcache_slow->cache_bin_array_descriptor, link);
		tcache_stats_merge(tsdn, tcache_slow->tcache, arena);
		malloc_mutex_unlock(tsdn, &arena->tcache_ql_mtx);
	}
	tcache_slow->arena = NULL;
}

void
tcache_arena_reassociate(tsdn_t *tsdn, tcache_slow_t *tcache_slow,
    tcache_t *tcache, arena_t *arena) {
	tcache_arena_dissociate(tsdn, tcache_slow, tcache);
	tcache_arena_associate(tsdn, tcache_slow, tcache, arena);
}

static void
tcache_default_settings_init(tcache_slow_t *tcache_slow) {
	assert(tcache_slow != NULL);
	assert(global_do_not_change_tcache_maxclass != 0);
	assert(global_do_not_change_tcache_nbins != 0);
	tcache_slow->tcache_nbins = global_do_not_change_tcache_nbins;
}

static void
tcache_init(tsd_t *tsd, tcache_slow_t *tcache_slow, tcache_t *tcache,
    void *mem, const cache_bin_info_t *tcache_bin_info) {
	tcache->tcache_slow = tcache_slow;
	tcache_slow->tcache = tcache;

	memset(&tcache_slow->link, 0, sizeof(ql_elm(tcache_t)));
	tcache_slow->next_gc_bin = 0;
	tcache_slow->arena = NULL;
	tcache_slow->dyn_alloc = mem;

	/*
	 * We reserve cache bins for all small size classes, even if some may
	 * not get used (i.e. bins higher than tcache_nbins).  This allows
	 * the fast and common paths to access cache bin metadata safely w/o
	 * worrying about which ones are disabled.
	 */
	unsigned tcache_nbins = tcache_nbins_get(tcache_slow);
	size_t cur_offset = 0;
	cache_bin_preincrement(tcache_bin_info, tcache_nbins, mem,
	    &cur_offset);
	for (unsigned i = 0; i < tcache_nbins; i++) {
		if (i < SC_NBINS) {
			tcache_slow->lg_fill_div[i] = 1;
			tcache_slow->bin_refilled[i] = false;
			tcache_slow->bin_flush_delay_items[i]
			    = tcache_gc_item_delay_compute(i);
		}
		cache_bin_t *cache_bin = &tcache->bins[i];
		if (tcache_bin_info[i].ncached_max > 0) {
			cache_bin_init(cache_bin, &tcache_bin_info[i], mem,
			    &cur_offset);
		} else {
			cache_bin_init_disabled(cache_bin,
			    tcache_bin_info[i].ncached_max);
		}
	}
	/*
	 * Initialize all disabled bins to a state that can safely and
	 * efficiently fail all fastpath alloc / free, so that no additional
	 * check around tcache_nbins is needed on fastpath.  Yet we still
	 * store the ncached_max in the bin_info for future usage.
	 */
	for (unsigned i = tcache_nbins; i < TCACHE_NBINS_MAX; i++) {
		cache_bin_t *cache_bin = &tcache->bins[i];
		cache_bin_init_disabled(cache_bin,
		    tcache_bin_info[i].ncached_max);
		assert(tcache_bin_disabled(i, cache_bin, tcache->tcache_slow));
	}

	cache_bin_postincrement(mem, &cur_offset);
	if (config_debug) {
		/* Sanity check that the whole stack is used. */
		size_t size, alignment;
		cache_bin_info_compute_alloc(tcache_bin_info, tcache_nbins,
		    &size, &alignment);
		assert(cur_offset == size);
	}
}

static inline unsigned
tcache_ncached_max_compute(szind_t szind) {
	if (szind >= SC_NBINS) {
		return opt_tcache_nslots_large;
	}
	unsigned slab_nregs = bin_infos[szind].nregs;

	/* We may modify these values; start with the opt versions. */
	unsigned nslots_small_min = opt_tcache_nslots_small_min;
	unsigned nslots_small_max = opt_tcache_nslots_small_max;

	/*
	 * Clamp values to meet our constraints -- even, nonzero, min < max, and
	 * suitable for a cache bin size.
	 */
	if (opt_tcache_nslots_small_max > CACHE_BIN_NCACHED_MAX) {
		nslots_small_max = CACHE_BIN_NCACHED_MAX;
	}
	if (nslots_small_min % 2 != 0) {
		nslots_small_min++;
	}
	if (nslots_small_max % 2 != 0) {
		nslots_small_max--;
	}
	if (nslots_small_min < 2) {
		nslots_small_min = 2;
	}
	if (nslots_small_max < 2) {
		nslots_small_max = 2;
	}
	if (nslots_small_min > nslots_small_max) {
		nslots_small_min = nslots_small_max;
	}

	unsigned candidate;
	if (opt_lg_tcache_nslots_mul < 0) {
		candidate = slab_nregs >> (-opt_lg_tcache_nslots_mul);
	} else {
		candidate = slab_nregs << opt_lg_tcache_nslots_mul;
	}
	if (candidate % 2 != 0) {
		/*
		 * We need the candidate size to be even -- we assume that we
		 * can divide by two and get a positive number (e.g. when
		 * flushing).
		 */
		++candidate;
	}
	if (candidate <= nslots_small_min) {
		return nslots_small_min;
	} else if (candidate <= nslots_small_max) {
		return candidate;
	} else {
		return nslots_small_max;
	}
}

JET_EXTERN void
tcache_bin_info_compute(cache_bin_info_t tcache_bin_info[TCACHE_NBINS_MAX]) {
	/*
	 * Compute the values for each bin, but for bins with indices larger
	 * than tcache_nbins, no items will be cached.
	 */
	for (szind_t i = 0; i < TCACHE_NBINS_MAX; i++) {
		unsigned ncached_max = tcache_get_default_ncached_max_set(i) ?
		    (unsigned)tcache_get_default_ncached_max()[i].ncached_max:
		    tcache_ncached_max_compute(i);
		assert(ncached_max <= CACHE_BIN_NCACHED_MAX);
		cache_bin_info_init(&tcache_bin_info[i],
		    (cache_bin_sz_t)ncached_max);
	}
}

static bool
tsd_tcache_data_init_impl(tsd_t *tsd, arena_t *arena,
    const cache_bin_info_t *tcache_bin_info) {
	tcache_slow_t *tcache_slow = tsd_tcache_slowp_get_unsafe(tsd);
	tcache_t *tcache = tsd_tcachep_get_unsafe(tsd);

	assert(cache_bin_still_zero_initialized(&tcache->bins[0]));
	unsigned tcache_nbins = tcache_nbins_get(tcache_slow);
	size_t size, alignment;
	cache_bin_info_compute_alloc(tcache_bin_info, tcache_nbins,
	    &size, &alignment);

	void *mem;
	if (cache_bin_stack_use_thp()) {
		/* Alignment is ignored since it comes from THP. */
		assert(alignment == QUANTUM);
		mem = b0_alloc_tcache_stack(tsd_tsdn(tsd), size);
	} else {
		size = sz_sa2u(size, alignment);
		mem = ipallocztm(tsd_tsdn(tsd), size, alignment, true, NULL,
		    true, arena_get(TSDN_NULL, 0, true));
	}
	if (mem == NULL) {
		return true;
	}

	tcache_init(tsd, tcache_slow, tcache, mem, tcache_bin_info);
	/*
	 * Initialization is a bit tricky here.  After malloc init is done, all
	 * threads can rely on arena_choose and associate tcache accordingly.
	 * However, the thread that does actual malloc bootstrapping relies on
	 * functional tsd, and it can only rely on a0.  In that case, we
	 * associate its tcache to a0 temporarily, and later on
	 * arena_choose_hard() will re-associate properly.
	 */
	tcache_slow->arena = NULL;
	if (!malloc_initialized()) {
		/* If in initialization, assign to a0. */
		arena = arena_get(tsd_tsdn(tsd), 0, false);
		tcache_arena_associate(tsd_tsdn(tsd), tcache_slow, tcache,
		    arena);
	} else {
		if (arena == NULL) {
			arena = arena_choose(tsd, NULL);
		}
		/* This may happen if thread.tcache.enabled is used. */
		if (tcache_slow->arena == NULL) {
			tcache_arena_associate(tsd_tsdn(tsd), tcache_slow,
			    tcache, arena);
		}
	}
	assert(arena == tcache_slow->arena);

	return false;
}

/* Initialize auto tcache (embedded in TSD). */
static bool
tsd_tcache_data_init(tsd_t *tsd, arena_t *arena,
    const cache_bin_info_t tcache_bin_info[TCACHE_NBINS_MAX]) {
	assert(tcache_bin_info != NULL);
	return tsd_tcache_data_init_impl(tsd, arena, tcache_bin_info);
}

/* Created manual tcache for tcache.create mallctl. */
tcache_t *
tcache_create_explicit(tsd_t *tsd) {
	/*
	 * We place the cache bin stacks, then the tcache_t, then a pointer to
	 * the beginning of the whole allocation (for freeing).  The makes sure
	 * the cache bins have the requested alignment.
	 */
	unsigned tcache_nbins = global_do_not_change_tcache_nbins;
	size_t tcache_size, alignment;
	cache_bin_info_compute_alloc(tcache_get_default_ncached_max(),
	    tcache_nbins, &tcache_size, &alignment);

	size_t size = tcache_size + sizeof(tcache_t)
	    + sizeof(tcache_slow_t);
	/* Naturally align the pointer stacks. */
	size = PTR_CEILING(size);
	size = sz_sa2u(size, alignment);

	void *mem = ipallocztm(tsd_tsdn(tsd), size, alignment,
	    true, NULL, true, arena_get(TSDN_NULL, 0, true));
	if (mem == NULL) {
		return NULL;
	}
	tcache_t *tcache = (void *)((byte_t *)mem + tcache_size);
	tcache_slow_t *tcache_slow =
	    (void *)((byte_t *)mem + tcache_size + sizeof(tcache_t));
	tcache_default_settings_init(tcache_slow);
	tcache_init(tsd, tcache_slow, tcache, mem,
	    tcache_get_default_ncached_max());

	tcache_arena_associate(tsd_tsdn(tsd), tcache_slow, tcache,
	    arena_ichoose(tsd, NULL));

	return tcache;
}

bool
tsd_tcache_enabled_data_init(tsd_t *tsd) {
	/* Called upon tsd initialization. */
	tsd_tcache_enabled_set(tsd, opt_tcache);
	/*
	 * tcache is not available yet, but we need to set up its tcache_nbins
	 * in advance.
	 */
	tcache_default_settings_init(tsd_tcache_slowp_get(tsd));
	tsd_slow_update(tsd);

	if (opt_tcache) {
		/* Trigger tcache init. */
		tsd_tcache_data_init(tsd, NULL,
		    tcache_get_default_ncached_max());
	}

	return false;
}

void
tcache_enabled_set(tsd_t *tsd, bool enabled) {
	bool was_enabled = tsd_tcache_enabled_get(tsd);

	if (!was_enabled && enabled) {
		tsd_tcache_data_init(tsd, NULL,
		    tcache_get_default_ncached_max());
	} else if (was_enabled && !enabled) {
		tcache_cleanup(tsd);
	}
	/* Commit the state last.  Above calls check current state. */
	tsd_tcache_enabled_set(tsd, enabled);
	tsd_slow_update(tsd);
}

void
thread_tcache_max_set(tsd_t *tsd, size_t tcache_max) {
	assert(tcache_max <= TCACHE_MAXCLASS_LIMIT);
	assert(tcache_max == sz_s2u(tcache_max));
	tcache_t *tcache = tsd_tcachep_get(tsd);
	tcache_slow_t *tcache_slow = tcache->tcache_slow;
	cache_bin_info_t tcache_bin_info[TCACHE_NBINS_MAX] = {{0}};
	assert(tcache != NULL && tcache_slow != NULL);

	bool enabled = tcache_available(tsd);
	arena_t *assigned_arena;
	if (enabled) {
		assigned_arena = tcache_slow->arena;
		/* Carry over the bin settings during the reboot. */
		tcache_bin_settings_backup(tcache, tcache_bin_info);
		/* Shutdown and reboot the tcache for a clean slate. */
		tcache_cleanup(tsd);
	}

	/*
	* Still set tcache_nbins of the tcache even if the tcache is not
	* available yet because the values are stored in tsd_t and are
	* always available for changing.
	*/
	tcache_max_set(tcache_slow, tcache_max);

	if (enabled) {
		tsd_tcache_data_init(tsd, assigned_arena, tcache_bin_info);
	}

	assert(tcache_nbins_get(tcache_slow) == sz_size2index(tcache_max) + 1);
}

static bool
tcache_bin_info_settings_parse(const char *bin_settings_segment_cur,
    size_t len_left, cache_bin_info_t tcache_bin_info[TCACHE_NBINS_MAX],
    bool bin_info_is_set[TCACHE_NBINS_MAX]) {
	do {
		size_t size_start, size_end;
		size_t ncached_max;
		bool err = multi_setting_parse_next(&bin_settings_segment_cur,
		    &len_left, &size_start, &size_end, &ncached_max);
		if (err) {
			return true;
		}
		if (size_end > TCACHE_MAXCLASS_LIMIT) {
			size_end = TCACHE_MAXCLASS_LIMIT;
		}
		if (size_start > TCACHE_MAXCLASS_LIMIT ||
		    size_start > size_end) {
			continue;
		}
		/* May get called before sz_init (during malloc_conf_init). */
		szind_t bin_start = sz_size2index_compute(size_start);
		szind_t bin_end = sz_size2index_compute(size_end);
		if (ncached_max > CACHE_BIN_NCACHED_MAX) {
			ncached_max = (size_t)CACHE_BIN_NCACHED_MAX;
		}
		for (szind_t i = bin_start; i <= bin_end; i++) {
			cache_bin_info_init(&tcache_bin_info[i],
			    (cache_bin_sz_t)ncached_max);
			if (bin_info_is_set != NULL) {
				bin_info_is_set[i] = true;
			}
		}
	} while (len_left > 0);

	return false;
}

bool
tcache_bin_info_default_init(const char *bin_settings_segment_cur,
    size_t len_left) {
	return tcache_bin_info_settings_parse(bin_settings_segment_cur,
	    len_left, opt_tcache_ncached_max, opt_tcache_ncached_max_set);
}


bool
tcache_bins_ncached_max_write(tsd_t *tsd, char *settings, size_t len) {
	assert(tcache_available(tsd));
	assert(len != 0);
	tcache_t *tcache = tsd_tcachep_get(tsd);
	assert(tcache != NULL);
	cache_bin_info_t tcache_bin_info[TCACHE_NBINS_MAX];
	tcache_bin_settings_backup(tcache, tcache_bin_info);

	if(tcache_bin_info_settings_parse(settings, len, tcache_bin_info,
	    NULL)) {
		return true;
	}

	arena_t *assigned_arena = tcache->tcache_slow->arena;
	tcache_cleanup(tsd);
	tsd_tcache_data_init(tsd, assigned_arena,
	    tcache_bin_info);

	return false;
}

static void
tcache_flush_cache(tsd_t *tsd, tcache_t *tcache) {
	tcache_slow_t *tcache_slow = tcache->tcache_slow;
	assert(tcache_slow->arena != NULL);

	for (unsigned i = 0; i < tcache_nbins_get(tcache_slow); i++) {
		cache_bin_t *cache_bin = &tcache->bins[i];
		if (tcache_bin_disabled(i, cache_bin, tcache_slow)) {
			continue;
		}
		if (i < SC_NBINS) {
			tcache_bin_flush_small(tsd, tcache, cache_bin, i, 0);
		} else {
			tcache_bin_flush_large(tsd, tcache, cache_bin, i, 0);
		}
		if (config_stats) {
			assert(cache_bin->tstats.nrequests == 0);
		}
	}
}

void
tcache_flush(tsd_t *tsd) {
	assert(tcache_available(tsd));
	tcache_flush_cache(tsd, tsd_tcachep_get(tsd));
}

static void
tcache_destroy(tsd_t *tsd, tcache_t *tcache, bool tsd_tcache) {
	tcache_slow_t *tcache_slow = tcache->tcache_slow;
	tcache_flush_cache(tsd, tcache);
	arena_t *arena = tcache_slow->arena;
	tcache_arena_dissociate(tsd_tsdn(tsd), tcache_slow, tcache);

	if (tsd_tcache) {
		cache_bin_t *cache_bin = &tcache->bins[0];
		cache_bin_assert_empty(cache_bin);
	}
	if (tsd_tcache && cache_bin_stack_use_thp()) {
		b0_dalloc_tcache_stack(tsd_tsdn(tsd), tcache_slow->dyn_alloc);
	} else {
		idalloctm(tsd_tsdn(tsd), tcache_slow->dyn_alloc, NULL, NULL,
		    true, true);
	}

	/*
	 * The deallocation and tcache flush above may not trigger decay since
	 * we are on the tcache shutdown path (potentially with non-nominal
	 * tsd).  Manually trigger decay to avoid pathological cases.  Also
	 * include arena 0 because the tcache array is allocated from it.
	 */
	arena_decay(tsd_tsdn(tsd), arena_get(tsd_tsdn(tsd), 0, false),
	    false, false);

	if (arena_nthreads_get(arena, false) == 0 &&
	    !background_thread_enabled()) {
		/* Force purging when no threads assigned to the arena anymore. */
		arena_decay(tsd_tsdn(tsd), arena,
		    /* is_background_thread */ false, /* all */ true);
	} else {
		arena_decay(tsd_tsdn(tsd), arena,
		    /* is_background_thread */ false, /* all */ false);
	}
}

/* For auto tcache (embedded in TSD) only. */
void
tcache_cleanup(tsd_t *tsd) {
	tcache_t *tcache = tsd_tcachep_get(tsd);
	if (!tcache_available(tsd)) {
		assert(tsd_tcache_enabled_get(tsd) == false);
		assert(cache_bin_still_zero_initialized(&tcache->bins[0]));
		return;
	}
	assert(tsd_tcache_enabled_get(tsd));
	assert(!cache_bin_still_zero_initialized(&tcache->bins[0]));

	tcache_destroy(tsd, tcache, true);
	/* Make sure all bins used are reinitialized to the clean state. */
	memset(tcache->bins, 0, sizeof(cache_bin_t) * TCACHE_NBINS_MAX);
}

void
tcache_stats_merge(tsdn_t *tsdn, tcache_t *tcache, arena_t *arena) {
	cassert(config_stats);

	/* Merge and reset tcache stats. */
	for (unsigned i = 0; i < tcache_nbins_get(tcache->tcache_slow); i++) {
		cache_bin_t *cache_bin = &tcache->bins[i];
		if (tcache_bin_disabled(i, cache_bin, tcache->tcache_slow)) {
			continue;
		}
		if (i < SC_NBINS) {
			bin_t *bin = arena_bin_choose(tsdn, arena, i, NULL);
			malloc_mutex_lock(tsdn, &bin->lock);
			bin->stats.nrequests += cache_bin->tstats.nrequests;
			malloc_mutex_unlock(tsdn, &bin->lock);
		} else {
			arena_stats_large_flush_nrequests_add(tsdn,
			    &arena->stats, i, cache_bin->tstats.nrequests);
		}
		cache_bin->tstats.nrequests = 0;
	}
}

static bool
tcaches_create_prep(tsd_t *tsd, base_t *base) {
	bool err;

	malloc_mutex_assert_owner(tsd_tsdn(tsd), &tcaches_mtx);

	if (tcaches == NULL) {
		tcaches = base_alloc(tsd_tsdn(tsd), base,
		    sizeof(tcache_t *) * (MALLOCX_TCACHE_MAX+1), CACHELINE);
		if (tcaches == NULL) {
			err = true;
			goto label_return;
		}
	}

	if (tcaches_avail == NULL && tcaches_past > MALLOCX_TCACHE_MAX) {
		err = true;
		goto label_return;
	}

	err = false;
label_return:
	return err;
}

bool
tcaches_create(tsd_t *tsd, base_t *base, unsigned *r_ind) {
	witness_assert_depth(tsdn_witness_tsdp_get(tsd_tsdn(tsd)), 0);

	bool err;

	malloc_mutex_lock(tsd_tsdn(tsd), &tcaches_mtx);

	if (tcaches_create_prep(tsd, base)) {
		err = true;
		goto label_return;
	}

	tcache_t *tcache = tcache_create_explicit(tsd);
	if (tcache == NULL) {
		err = true;
		goto label_return;
	}

	tcaches_t *elm;
	if (tcaches_avail != NULL) {
		elm = tcaches_avail;
		tcaches_avail = tcaches_avail->next;
		elm->tcache = tcache;
		*r_ind = (unsigned)(elm - tcaches);
	} else {
		elm = &tcaches[tcaches_past];
		elm->tcache = tcache;
		*r_ind = tcaches_past;
		tcaches_past++;
	}

	err = false;
label_return:
	malloc_mutex_unlock(tsd_tsdn(tsd), &tcaches_mtx);
	witness_assert_depth(tsdn_witness_tsdp_get(tsd_tsdn(tsd)), 0);
	return err;
}

static tcache_t *
tcaches_elm_remove(tsd_t *tsd, tcaches_t *elm, bool allow_reinit) {
	malloc_mutex_assert_owner(tsd_tsdn(tsd), &tcaches_mtx);

	if (elm->tcache == NULL) {
		return NULL;
	}
	tcache_t *tcache = elm->tcache;
	if (allow_reinit) {
		elm->tcache = TCACHES_ELM_NEED_REINIT;
	} else {
		elm->tcache = NULL;
	}

	if (tcache == TCACHES_ELM_NEED_REINIT) {
		return NULL;
	}
	return tcache;
}

void
tcaches_flush(tsd_t *tsd, unsigned ind) {
	malloc_mutex_lock(tsd_tsdn(tsd), &tcaches_mtx);
	tcache_t *tcache = tcaches_elm_remove(tsd, &tcaches[ind], true);
	malloc_mutex_unlock(tsd_tsdn(tsd), &tcaches_mtx);
	if (tcache != NULL) {
		/* Destroy the tcache; recreate in tcaches_get() if needed. */
		tcache_destroy(tsd, tcache, false);
	}
}

void
tcaches_destroy(tsd_t *tsd, unsigned ind) {
	malloc_mutex_lock(tsd_tsdn(tsd), &tcaches_mtx);
	tcaches_t *elm = &tcaches[ind];
	tcache_t *tcache = tcaches_elm_remove(tsd, elm, false);
	elm->next = tcaches_avail;
	tcaches_avail = elm;
	malloc_mutex_unlock(tsd_tsdn(tsd), &tcaches_mtx);
	if (tcache != NULL) {
		tcache_destroy(tsd, tcache, false);
	}
}

bool
tcache_boot(tsdn_t *tsdn, base_t *base) {
	global_do_not_change_tcache_maxclass = sz_s2u(opt_tcache_max);
	assert(global_do_not_change_tcache_maxclass <= TCACHE_MAXCLASS_LIMIT);
	global_do_not_change_tcache_nbins =
	    sz_size2index(global_do_not_change_tcache_maxclass) + 1;
	/*
	 * Pre-compute default bin info and store the results in
	 * opt_tcache_ncached_max. After the changes here,
	 * opt_tcache_ncached_max should not be modified and should always be
	 * accessed using tcache_get_default_ncached_max.
	 */
	tcache_bin_info_compute(opt_tcache_ncached_max);

	if (malloc_mutex_init(&tcaches_mtx, "tcaches", WITNESS_RANK_TCACHES,
	    malloc_mutex_rank_exclusive)) {
		return true;
	}

	return false;
}

void
tcache_prefork(tsdn_t *tsdn) {
	malloc_mutex_prefork(tsdn, &tcaches_mtx);
}

void
tcache_postfork_parent(tsdn_t *tsdn) {
	malloc_mutex_postfork_parent(tsdn, &tcaches_mtx);
}

void
tcache_postfork_child(tsdn_t *tsdn) {
	malloc_mutex_postfork_child(tsdn, &tcaches_mtx);
}

void tcache_assert_initialized(tcache_t *tcache) {
	assert(!cache_bin_still_zero_initialized(&tcache->bins[0]));
}