1 files changed, 231 insertions, 553 deletions

diff --git a/deps/jemalloc/test/unit/decay.c b/deps/jemalloc/test/unit/decay.c
index cf3c07960..bdb6d0a39 100644
--- a/deps/jemalloc/test/unit/decay.c
+++ b/deps/jemalloc/test/unit/decay.c
@@ -1,605 +1,283 @@
 #include "test/jemalloc_test.h"
 
-#include "jemalloc/internal/ticker.h"
-
-static nstime_monotonic_t *nstime_monotonic_orig;
-static nstime_update_t *nstime_update_orig;
-
-static unsigned nupdates_mock;
-static nstime_t time_mock;
-static bool monotonic_mock;
-
-static bool
-check_background_thread_enabled(void) {
-	bool enabled;
-	size_t sz = sizeof(bool);
-	int ret = mallctl("background_thread", (void *)&enabled, &sz, NULL,0);
-	if (ret == ENOENT) {
-		return false;
-	}
-	assert_d_eq(ret, 0, "Unexpected mallctl error");
-	return enabled;
-}
+#include "jemalloc/internal/decay.h"
 
-static bool
-nstime_monotonic_mock(void) {
-	return monotonic_mock;
-}
+TEST_BEGIN(test_decay_init) {
+	decay_t decay;
+	memset(&decay, 0, sizeof(decay));
 
-static bool
-nstime_update_mock(nstime_t *time) {
-	nupdates_mock++;
-	if (monotonic_mock) {
-		nstime_copy(time, &time_mock);
-	}
-	return !monotonic_mock;
-}
+	nstime_t curtime;
+	nstime_init(&curtime, 0);
 
-static unsigned
-do_arena_create(ssize_t dirty_decay_ms, ssize_t muzzy_decay_ms) {
-	unsigned arena_ind;
-	size_t sz = sizeof(unsigned);
-	assert_d_eq(mallctl("arenas.create", (void *)&arena_ind, &sz, NULL, 0),
-	    0, "Unexpected mallctl() failure");
-	size_t mib[3];
-	size_t miblen = sizeof(mib)/sizeof(size_t);
-
-	assert_d_eq(mallctlnametomib("arena.0.dirty_decay_ms", mib, &miblen),
-	    0, "Unexpected mallctlnametomib() failure");
-	mib[1] = (size_t)arena_ind;
-	assert_d_eq(mallctlbymib(mib, miblen, NULL, NULL,
-	    (void *)&dirty_decay_ms, sizeof(dirty_decay_ms)), 0,
-	    "Unexpected mallctlbymib() failure");
-
-	assert_d_eq(mallctlnametomib("arena.0.muzzy_decay_ms", mib, &miblen),
-	    0, "Unexpected mallctlnametomib() failure");
-	mib[1] = (size_t)arena_ind;
-	assert_d_eq(mallctlbymib(mib, miblen, NULL, NULL,
-	    (void *)&muzzy_decay_ms, sizeof(muzzy_decay_ms)), 0,
-	    "Unexpected mallctlbymib() failure");
-
-	return arena_ind;
-}
+	ssize_t decay_ms = 1000;
+	assert_true(decay_ms_valid(decay_ms), "");
 
-static void
-do_arena_destroy(unsigned arena_ind) {
-	size_t mib[3];
-	size_t miblen = sizeof(mib)/sizeof(size_t);
-	assert_d_eq(mallctlnametomib("arena.0.destroy", mib, &miblen), 0,
-	    "Unexpected mallctlnametomib() failure");
-	mib[1] = (size_t)arena_ind;
-	assert_d_eq(mallctlbymib(mib, miblen, NULL, NULL, NULL, 0), 0,
-	    "Unexpected mallctlbymib() failure");
+	expect_false(decay_init(&decay, &curtime, decay_ms),
+	    "Failed to initialize decay");
+	expect_zd_eq(decay_ms_read(&decay), decay_ms,
+	    "Decay_ms was initialized incorrectly");
+	expect_u64_ne(decay_epoch_duration_ns(&decay), 0,
+	    "Epoch duration was initialized incorrectly");
 }
+TEST_END
 
-void
-do_epoch(void) {
-	uint64_t epoch = 1;
-	assert_d_eq(mallctl("epoch", NULL, NULL, (void *)&epoch, sizeof(epoch)),
-	    0, "Unexpected mallctl() failure");
+TEST_BEGIN(test_decay_ms_valid) {
+	expect_false(decay_ms_valid(-7),
+	    "Misclassified negative decay as valid");
+	expect_true(decay_ms_valid(-1),
+	    "Misclassified -1 (never decay) as invalid decay");
+	expect_true(decay_ms_valid(8943),
+	    "Misclassified valid decay");
+	if (SSIZE_MAX > NSTIME_SEC_MAX) {
+		expect_false(
+		    decay_ms_valid((ssize_t)(NSTIME_SEC_MAX * KQU(1000) + 39)),
+		    "Misclassified too large decay");
+	}
 }
+TEST_END
 
-void
-do_purge(unsigned arena_ind) {
-	size_t mib[3];
-	size_t miblen = sizeof(mib)/sizeof(size_t);
-	assert_d_eq(mallctlnametomib("arena.0.purge", mib, &miblen), 0,
-	    "Unexpected mallctlnametomib() failure");
-	mib[1] = (size_t)arena_ind;
-	assert_d_eq(mallctlbymib(mib, miblen, NULL, NULL, NULL, 0), 0,
-	    "Unexpected mallctlbymib() failure");
-}
+TEST_BEGIN(test_decay_npages_purge_in) {
+	decay_t decay;
+	memset(&decay, 0, sizeof(decay));
 
-void
-do_decay(unsigned arena_ind) {
-	size_t mib[3];
-	size_t miblen = sizeof(mib)/sizeof(size_t);
-	assert_d_eq(mallctlnametomib("arena.0.decay", mib, &miblen), 0,
-	    "Unexpected mallctlnametomib() failure");
-	mib[1] = (size_t)arena_ind;
-	assert_d_eq(mallctlbymib(mib, miblen, NULL, NULL, NULL, 0), 0,
-	    "Unexpected mallctlbymib() failure");
-}
+	nstime_t curtime;
+	nstime_init(&curtime, 0);
 
-static uint64_t
-get_arena_npurge_impl(const char *mibname, unsigned arena_ind) {
-	size_t mib[4];
-	size_t miblen = sizeof(mib)/sizeof(size_t);
-	assert_d_eq(mallctlnametomib(mibname, mib, &miblen), 0,
-	    "Unexpected mallctlnametomib() failure");
-	mib[2] = (size_t)arena_ind;
-	uint64_t npurge = 0;
-	size_t sz = sizeof(npurge);
-	assert_d_eq(mallctlbymib(mib, miblen, (void *)&npurge, &sz, NULL, 0),
-	    config_stats ? 0 : ENOENT, "Unexpected mallctlbymib() failure");
-	return npurge;
-}
+	uint64_t decay_ms = 1000;
+	nstime_t decay_nstime;
+	nstime_init(&decay_nstime, decay_ms * 1000 * 1000);
+	expect_false(decay_init(&decay, &curtime, (ssize_t)decay_ms),
+	    "Failed to initialize decay");
 
-static uint64_t
-get_arena_dirty_npurge(unsigned arena_ind) {
-	do_epoch();
-	return get_arena_npurge_impl("stats.arenas.0.dirty_npurge", arena_ind);
-}
+	size_t new_pages = 100;
 
-static uint64_t
-get_arena_dirty_purged(unsigned arena_ind) {
-	do_epoch();
-	return get_arena_npurge_impl("stats.arenas.0.dirty_purged", arena_ind);
-}
+	nstime_t time;
+	nstime_copy(&time, &decay_nstime);
+	expect_u64_eq(decay_npages_purge_in(&decay, &time, new_pages),
+	    new_pages, "Not all pages are expected to decay in decay_ms");
 
-static uint64_t
-get_arena_muzzy_npurge(unsigned arena_ind) {
-	do_epoch();
-	return get_arena_npurge_impl("stats.arenas.0.muzzy_npurge", arena_ind);
-}
+	nstime_init(&time, 0);
+	expect_u64_eq(decay_npages_purge_in(&decay, &time, new_pages), 0,
+	    "More than zero pages are expected to instantly decay");
 
-static uint64_t
-get_arena_npurge(unsigned arena_ind) {
-	do_epoch();
-	return get_arena_npurge_impl("stats.arenas.0.dirty_npurge", arena_ind) +
-	    get_arena_npurge_impl("stats.arenas.0.muzzy_npurge", arena_ind);
+	nstime_copy(&time, &decay_nstime);
+	nstime_idivide(&time, 2);
+	expect_u64_eq(decay_npages_purge_in(&decay, &time, new_pages),
+	    new_pages / 2, "Not half of pages decay in half the decay period");
 }
+TEST_END
 
-static size_t
-get_arena_pdirty(unsigned arena_ind) {
-	do_epoch();
-	size_t mib[4];
-	size_t miblen = sizeof(mib)/sizeof(size_t);
-	assert_d_eq(mallctlnametomib("stats.arenas.0.pdirty", mib, &miblen), 0,
-	    "Unexpected mallctlnametomib() failure");
-	mib[2] = (size_t)arena_ind;
-	size_t pdirty;
-	size_t sz = sizeof(pdirty);
-	assert_d_eq(mallctlbymib(mib, miblen, (void *)&pdirty, &sz, NULL, 0), 0,
-	    "Unexpected mallctlbymib() failure");
-	return pdirty;
-}
+TEST_BEGIN(test_decay_maybe_advance_epoch) {
+	decay_t decay;
+	memset(&decay, 0, sizeof(decay));
 
-static size_t
-get_arena_pmuzzy(unsigned arena_ind) {
-	do_epoch();
-	size_t mib[4];
-	size_t miblen = sizeof(mib)/sizeof(size_t);
-	assert_d_eq(mallctlnametomib("stats.arenas.0.pmuzzy", mib, &miblen), 0,
-	    "Unexpected mallctlnametomib() failure");
-	mib[2] = (size_t)arena_ind;
-	size_t pmuzzy;
-	size_t sz = sizeof(pmuzzy);
-	assert_d_eq(mallctlbymib(mib, miblen, (void *)&pmuzzy, &sz, NULL, 0), 0,
-	    "Unexpected mallctlbymib() failure");
-	return pmuzzy;
-}
+	nstime_t curtime;
+	nstime_init(&curtime, 0);
 
-static void *
-do_mallocx(size_t size, int flags) {
-	void *p = mallocx(size, flags);
-	assert_ptr_not_null(p, "Unexpected mallocx() failure");
-	return p;
-}
+	uint64_t decay_ms = 1000;
 
-static void
-generate_dirty(unsigned arena_ind, size_t size) {
-	int flags = MALLOCX_ARENA(arena_ind) | MALLOCX_TCACHE_NONE;
-	void *p = do_mallocx(size, flags);
-	dallocx(p, flags);
-}
+	bool err = decay_init(&decay, &curtime, (ssize_t)decay_ms);
+	expect_false(err, "");
 
-TEST_BEGIN(test_decay_ticks) {
-	test_skip_if(check_background_thread_enabled());
-
-	ticker_t *decay_ticker;
-	unsigned tick0, tick1, arena_ind;
-	size_t sz, large0;
-	void *p;
-
-	sz = sizeof(size_t);
-	assert_d_eq(mallctl("arenas.lextent.0.size", (void *)&large0, &sz, NULL,
-	    0), 0, "Unexpected mallctl failure");
-
-	/* Set up a manually managed arena for test. */
-	arena_ind = do_arena_create(0, 0);
-
-	/* Migrate to the new arena, and get the ticker. */
-	unsigned old_arena_ind;
-	size_t sz_arena_ind = sizeof(old_arena_ind);
-	assert_d_eq(mallctl("thread.arena", (void *)&old_arena_ind,
-	    &sz_arena_ind, (void *)&arena_ind, sizeof(arena_ind)), 0,
-	    "Unexpected mallctl() failure");
-	decay_ticker = decay_ticker_get(tsd_fetch(), arena_ind);
-	assert_ptr_not_null(decay_ticker,
-	    "Unexpected failure getting decay ticker");
-
-	/*
-	 * Test the standard APIs using a large size class, since we can't
-	 * control tcache interactions for small size classes (except by
-	 * completely disabling tcache for the entire test program).
-	 */
-
-	/* malloc(). */
-	tick0 = ticker_read(decay_ticker);
-	p = malloc(large0);
-	assert_ptr_not_null(p, "Unexpected malloc() failure");
-	tick1 = ticker_read(decay_ticker);
-	assert_u32_ne(tick1, tick0, "Expected ticker to tick during malloc()");
-	/* free(). */
-	tick0 = ticker_read(decay_ticker);
-	free(p);
-	tick1 = ticker_read(decay_ticker);
-	assert_u32_ne(tick1, tick0, "Expected ticker to tick during free()");
-
-	/* calloc(). */
-	tick0 = ticker_read(decay_ticker);
-	p = calloc(1, large0);
-	assert_ptr_not_null(p, "Unexpected calloc() failure");
-	tick1 = ticker_read(decay_ticker);
-	assert_u32_ne(tick1, tick0, "Expected ticker to tick during calloc()");
-	free(p);
-
-	/* posix_memalign(). */
-	tick0 = ticker_read(decay_ticker);
-	assert_d_eq(posix_memalign(&p, sizeof(size_t), large0), 0,
-	    "Unexpected posix_memalign() failure");
-	tick1 = ticker_read(decay_ticker);
-	assert_u32_ne(tick1, tick0,
-	    "Expected ticker to tick during posix_memalign()");
-	free(p);
-
-	/* aligned_alloc(). */
-	tick0 = ticker_read(decay_ticker);
-	p = aligned_alloc(sizeof(size_t), large0);
-	assert_ptr_not_null(p, "Unexpected aligned_alloc() failure");
-	tick1 = ticker_read(decay_ticker);
-	assert_u32_ne(tick1, tick0,
-	    "Expected ticker to tick during aligned_alloc()");
-	free(p);
-
-	/* realloc(). */
-	/* Allocate. */
-	tick0 = ticker_read(decay_ticker);
-	p = realloc(NULL, large0);
-	assert_ptr_not_null(p, "Unexpected realloc() failure");
-	tick1 = ticker_read(decay_ticker);
-	assert_u32_ne(tick1, tick0, "Expected ticker to tick during realloc()");
-	/* Reallocate. */
-	tick0 = ticker_read(decay_ticker);
-	p = realloc(p, large0);
-	assert_ptr_not_null(p, "Unexpected realloc() failure");
-	tick1 = ticker_read(decay_ticker);
-	assert_u32_ne(tick1, tick0, "Expected ticker to tick during realloc()");
-	/* Deallocate. */
-	tick0 = ticker_read(decay_ticker);
-	realloc(p, 0);
-	tick1 = ticker_read(decay_ticker);
-	assert_u32_ne(tick1, tick0, "Expected ticker to tick during realloc()");
-
-	/*
-	 * Test the *allocx() APIs using large and small size classes, with
-	 * tcache explicitly disabled.
-	 */
-	{
-		unsigned i;
-		size_t allocx_sizes[2];
-		allocx_sizes[0] = large0;
-		allocx_sizes[1] = 1;
-
-		for (i = 0; i < sizeof(allocx_sizes) / sizeof(size_t); i++) {
-			sz = allocx_sizes[i];
-
-			/* mallocx(). */
-			tick0 = ticker_read(decay_ticker);
-			p = mallocx(sz, MALLOCX_TCACHE_NONE);
-			assert_ptr_not_null(p, "Unexpected mallocx() failure");
-			tick1 = ticker_read(decay_ticker);
-			assert_u32_ne(tick1, tick0,
-			    "Expected ticker to tick during mallocx() (sz=%zu)",
-			    sz);
-			/* rallocx(). */
-			tick0 = ticker_read(decay_ticker);
-			p = rallocx(p, sz, MALLOCX_TCACHE_NONE);
-			assert_ptr_not_null(p, "Unexpected rallocx() failure");
-			tick1 = ticker_read(decay_ticker);
-			assert_u32_ne(tick1, tick0,
-			    "Expected ticker to tick during rallocx() (sz=%zu)",
-			    sz);
-			/* xallocx(). */
-			tick0 = ticker_read(decay_ticker);
-			xallocx(p, sz, 0, MALLOCX_TCACHE_NONE);
-			tick1 = ticker_read(decay_ticker);
-			assert_u32_ne(tick1, tick0,
-			    "Expected ticker to tick during xallocx() (sz=%zu)",
-			    sz);
-			/* dallocx(). */
-			tick0 = ticker_read(decay_ticker);
-			dallocx(p, MALLOCX_TCACHE_NONE);
-			tick1 = ticker_read(decay_ticker);
-			assert_u32_ne(tick1, tick0,
-			    "Expected ticker to tick during dallocx() (sz=%zu)",
-			    sz);
-			/* sdallocx(). */
-			p = mallocx(sz, MALLOCX_TCACHE_NONE);
-			assert_ptr_not_null(p, "Unexpected mallocx() failure");
-			tick0 = ticker_read(decay_ticker);
-			sdallocx(p, sz, MALLOCX_TCACHE_NONE);
-			tick1 = ticker_read(decay_ticker);
-			assert_u32_ne(tick1, tick0,
-			    "Expected ticker to tick during sdallocx() "
-			    "(sz=%zu)", sz);
-		}
-	}
+	bool advanced;
+	advanced = decay_maybe_advance_epoch(&decay, &curtime, 0);
+	expect_false(advanced, "Epoch advanced while time didn't");
 
-	/*
-	 * Test tcache fill/flush interactions for large and small size classes,
-	 * using an explicit tcache.
-	 */
-	unsigned tcache_ind, i;
-	size_t tcache_sizes[2];
-	tcache_sizes[0] = large0;
-	tcache_sizes[1] = 1;
-
-	size_t tcache_max, sz_tcache_max;
-	sz_tcache_max = sizeof(tcache_max);
-	assert_d_eq(mallctl("arenas.tcache_max", (void *)&tcache_max,
-	    &sz_tcache_max, NULL, 0), 0, "Unexpected mallctl() failure");
-
-	sz = sizeof(unsigned);
-	assert_d_eq(mallctl("tcache.create", (void *)&tcache_ind, &sz,
-	    NULL, 0), 0, "Unexpected mallctl failure");
-
-	for (i = 0; i < sizeof(tcache_sizes) / sizeof(size_t); i++) {
-		sz = tcache_sizes[i];
-
-		/* tcache fill. */
-		tick0 = ticker_read(decay_ticker);
-		p = mallocx(sz, MALLOCX_TCACHE(tcache_ind));
-		assert_ptr_not_null(p, "Unexpected mallocx() failure");
-		tick1 = ticker_read(decay_ticker);
-		assert_u32_ne(tick1, tick0,
-		    "Expected ticker to tick during tcache fill "
-		    "(sz=%zu)", sz);
-		/* tcache flush. */
-		dallocx(p, MALLOCX_TCACHE(tcache_ind));
-		tick0 = ticker_read(decay_ticker);
-		assert_d_eq(mallctl("tcache.flush", NULL, NULL,
-		    (void *)&tcache_ind, sizeof(unsigned)), 0,
-		    "Unexpected mallctl failure");
-		tick1 = ticker_read(decay_ticker);
-
-		/* Will only tick if it's in tcache. */
-		if (sz <= tcache_max) {
-			assert_u32_ne(tick1, tick0,
-			    "Expected ticker to tick during tcache "
-			    "flush (sz=%zu)", sz);
-		} else {
-			assert_u32_eq(tick1, tick0,
-			    "Unexpected ticker tick during tcache "
-			    "flush (sz=%zu)", sz);
-		}
-	}
+	nstime_t interval;
+	nstime_init(&interval, decay_epoch_duration_ns(&decay));
+
+	nstime_add(&curtime, &interval);
+	advanced = decay_maybe_advance_epoch(&decay, &curtime, 0);
+	expect_false(advanced, "Epoch advanced after first interval");
+
+	nstime_add(&curtime, &interval);
+	advanced = decay_maybe_advance_epoch(&decay, &curtime, 0);
+	expect_true(advanced, "Epoch didn't advance after two intervals");
 }
 TEST_END
 
-static void
-decay_ticker_helper(unsigned arena_ind, int flags, bool dirty, ssize_t dt,
-    uint64_t dirty_npurge0, uint64_t muzzy_npurge0, bool terminate_asap) {
-#define NINTERVALS 101
-	nstime_t time, update_interval, decay_ms, deadline;
-
-	nstime_init(&time, 0);
-	nstime_update(&time);
-
-	nstime_init2(&decay_ms, dt, 0);
-	nstime_copy(&deadline, &time);
-	nstime_add(&deadline, &decay_ms);
-
-	nstime_init2(&update_interval, dt, 0);
-	nstime_idivide(&update_interval, NINTERVALS);
-
-	/*
-	 * Keep q's slab from being deallocated during the looping below.  If a
-	 * cached slab were to repeatedly come and go during looping, it could
-	 * prevent the decay backlog ever becoming empty.
-	 */
-	void *p = do_mallocx(1, flags);
-	uint64_t dirty_npurge1, muzzy_npurge1;
-	do {
-		for (unsigned i = 0; i < DECAY_NTICKS_PER_UPDATE / 2;
-		    i++) {
-			void *q = do_mallocx(1, flags);
-			dallocx(q, flags);
+TEST_BEGIN(test_decay_empty) {
+	/* If we never have any decaying pages, npages_limit should be 0. */
+	decay_t decay;
+	memset(&decay, 0, sizeof(decay));
+
+	nstime_t curtime;
+	nstime_init(&curtime, 0);
+
+	uint64_t decay_ms = 1000;
+	uint64_t decay_ns = decay_ms * 1000 * 1000;
+
+	bool err = decay_init(&decay, &curtime, (ssize_t)decay_ms);
+	assert_false(err, "");
+
+	uint64_t time_between_calls = decay_epoch_duration_ns(&decay) / 5;
+	int nepochs = 0;
+	for (uint64_t i = 0; i < decay_ns / time_between_calls * 10; i++) {
+		size_t dirty_pages = 0;
+		nstime_init(&curtime, i * time_between_calls);
+		bool epoch_advanced = decay_maybe_advance_epoch(&decay,
+		    &curtime, dirty_pages);
+		if (epoch_advanced) {
+			nepochs++;
+			expect_zu_eq(decay_npages_limit_get(&decay), 0,
+			    "Unexpectedly increased npages_limit");
 		}
-		dirty_npurge1 = get_arena_dirty_npurge(arena_ind);
-		muzzy_npurge1 = get_arena_muzzy_npurge(arena_ind);
-
-		nstime_add(&time_mock, &update_interval);
-		nstime_update(&time);
-	} while (nstime_compare(&time, &deadline) <= 0 && ((dirty_npurge1 ==
-	    dirty_npurge0 && muzzy_npurge1 == muzzy_npurge0) ||
-	    !terminate_asap));
-	dallocx(p, flags);
-
-	if (config_stats) {
-		assert_u64_gt(dirty_npurge1 + muzzy_npurge1, dirty_npurge0 +
-		    muzzy_npurge0, "Expected purging to occur");
 	}
-#undef NINTERVALS
+	expect_d_gt(nepochs, 0, "Epochs never advanced");
 }
+TEST_END
 
-TEST_BEGIN(test_decay_ticker) {
-	test_skip_if(check_background_thread_enabled());
-#define NPS 2048
-	ssize_t ddt = opt_dirty_decay_ms;
-	ssize_t mdt = opt_muzzy_decay_ms;
-	unsigned arena_ind = do_arena_create(ddt, mdt);
-	int flags = (MALLOCX_ARENA(arena_ind) | MALLOCX_TCACHE_NONE);
-	void *ps[NPS];
-	size_t large;
-
-	/*
-	 * Allocate a bunch of large objects, pause the clock, deallocate every
-	 * other object (to fragment virtual memory), restore the clock, then
-	 * [md]allocx() in a tight loop while advancing time rapidly to verify
-	 * the ticker triggers purging.
-	 */
-
-	size_t tcache_max;
-	size_t sz = sizeof(size_t);
-	assert_d_eq(mallctl("arenas.tcache_max", (void *)&tcache_max, &sz, NULL,
-	    0), 0, "Unexpected mallctl failure");
-	large = nallocx(tcache_max + 1, flags);
-
-	do_purge(arena_ind);
-	uint64_t dirty_npurge0 = get_arena_dirty_npurge(arena_ind);
-	uint64_t muzzy_npurge0 = get_arena_muzzy_npurge(arena_ind);
-
-	for (unsigned i = 0; i < NPS; i++) {
-		ps[i] = do_mallocx(large, flags);
+/*
+ * Verify that npages_limit correctly decays as the time goes.
+ *
+ * During first 'nepoch_init' epochs, add new dirty pages.
+ * After that, let them decay and verify npages_limit decreases.
+ * Then proceed with another 'nepoch_init' epochs and check that
+ * all dirty pages are flushed out of backlog, bringing npages_limit
+ * down to zero.
+ */
+TEST_BEGIN(test_decay) {
+	const uint64_t nepoch_init = 10;
+
+	decay_t decay;
+	memset(&decay, 0, sizeof(decay));
+
+	nstime_t curtime;
+	nstime_init(&curtime, 0);
+
+	uint64_t decay_ms = 1000;
+	uint64_t decay_ns = decay_ms * 1000 * 1000;
+
+	bool err = decay_init(&decay, &curtime, (ssize_t)decay_ms);
+	assert_false(err, "");
+
+	expect_zu_eq(decay_npages_limit_get(&decay), 0,
+	    "Empty decay returned nonzero npages_limit");
+
+	nstime_t epochtime;
+	nstime_init(&epochtime, decay_epoch_duration_ns(&decay));
+
+	const size_t dirty_pages_per_epoch = 1000;
+	size_t dirty_pages = 0;
+	uint64_t epoch_ns = decay_epoch_duration_ns(&decay);
+	bool epoch_advanced = false;
+
+	/* Populate backlog with some dirty pages */
+	for (uint64_t i = 0; i < nepoch_init; i++) {
+		nstime_add(&curtime, &epochtime);
+		dirty_pages += dirty_pages_per_epoch;
+		epoch_advanced |= decay_maybe_advance_epoch(&decay, &curtime,
+		    dirty_pages);
 	}
-
-	nupdates_mock = 0;
-	nstime_init(&time_mock, 0);
-	nstime_update(&time_mock);
-	monotonic_mock = true;
-
-	nstime_monotonic_orig = nstime_monotonic;
-	nstime_update_orig = nstime_update;
-	nstime_monotonic = nstime_monotonic_mock;
-	nstime_update = nstime_update_mock;
-
-	for (unsigned i = 0; i < NPS; i += 2) {
-		dallocx(ps[i], flags);
-		unsigned nupdates0 = nupdates_mock;
-		do_decay(arena_ind);
-		assert_u_gt(nupdates_mock, nupdates0,
-		    "Expected nstime_update() to be called");
+	expect_true(epoch_advanced, "Epoch never advanced");
+
+	size_t npages_limit = decay_npages_limit_get(&decay);
+	expect_zu_gt(npages_limit, 0, "npages_limit is incorrectly equal "
+	    "to zero after dirty pages have been added");
+
+	/* Keep dirty pages unchanged and verify that npages_limit decreases */
+	for (uint64_t i = nepoch_init; i * epoch_ns < decay_ns; ++i) {
+		nstime_add(&curtime, &epochtime);
+		epoch_advanced = decay_maybe_advance_epoch(&decay, &curtime,
+				    dirty_pages);
+		if (epoch_advanced) {
+			size_t npages_limit_new = decay_npages_limit_get(&decay);
+			expect_zu_lt(npages_limit_new, npages_limit,
+			    "napges_limit failed to decay");
+
+			npages_limit = npages_limit_new;
+		}
 	}
 
-	decay_ticker_helper(arena_ind, flags, true, ddt, dirty_npurge0,
-	    muzzy_npurge0, true);
-	decay_ticker_helper(arena_ind, flags, false, ddt+mdt, dirty_npurge0,
-	    muzzy_npurge0, false);
+	expect_zu_gt(npages_limit, 0, "npages_limit decayed to zero earlier "
+	    "than decay_ms since last dirty page was added");
 
-	do_arena_destroy(arena_ind);
+	/* Completely push all dirty pages out of the backlog */
+	epoch_advanced = false;
+	for (uint64_t i = 0; i < nepoch_init; i++) {
+		nstime_add(&curtime, &epochtime);
+		epoch_advanced |= decay_maybe_advance_epoch(&decay, &curtime,
+		    dirty_pages);
+	}
+	expect_true(epoch_advanced, "Epoch never advanced");
 
-	nstime_monotonic = nstime_monotonic_orig;
-	nstime_update = nstime_update_orig;
-#undef NPS
+	npages_limit = decay_npages_limit_get(&decay);
+	expect_zu_eq(npages_limit, 0, "npages_limit didn't decay to 0 after "
+	    "decay_ms since last bump in dirty pages");
 }
 TEST_END
 
-TEST_BEGIN(test_decay_nonmonotonic) {
-	test_skip_if(check_background_thread_enabled());
-#define NPS (SMOOTHSTEP_NSTEPS + 1)
-	int flags = (MALLOCX_ARENA(0) | MALLOCX_TCACHE_NONE);
-	void *ps[NPS];
-	uint64_t npurge0 = 0;
-	uint64_t npurge1 = 0;
-	size_t sz, large0;
-	unsigned i, nupdates0;
-
-	sz = sizeof(size_t);
-	assert_d_eq(mallctl("arenas.lextent.0.size", (void *)&large0, &sz, NULL,
-	    0), 0, "Unexpected mallctl failure");
-
-	assert_d_eq(mallctl("arena.0.purge", NULL, NULL, NULL, 0), 0,
-	    "Unexpected mallctl failure");
-	do_epoch();
-	sz = sizeof(uint64_t);
-	npurge0 = get_arena_npurge(0);
-
-	nupdates_mock = 0;
-	nstime_init(&time_mock, 0);
-	nstime_update(&time_mock);
-	monotonic_mock = false;
-
-	nstime_monotonic_orig = nstime_monotonic;
-	nstime_update_orig = nstime_update;
-	nstime_monotonic = nstime_monotonic_mock;
-	nstime_update = nstime_update_mock;
-
-	for (i = 0; i < NPS; i++) {
-		ps[i] = mallocx(large0, flags);
-		assert_ptr_not_null(ps[i], "Unexpected mallocx() failure");
-	}
+TEST_BEGIN(test_decay_ns_until_purge) {
+	const uint64_t nepoch_init = 10;
 
-	for (i = 0; i < NPS; i++) {
-		dallocx(ps[i], flags);
-		nupdates0 = nupdates_mock;
-		assert_d_eq(mallctl("arena.0.decay", NULL, NULL, NULL, 0), 0,
-		    "Unexpected arena.0.decay failure");
-		assert_u_gt(nupdates_mock, nupdates0,
-		    "Expected nstime_update() to be called");
-	}
+	decay_t decay;
+	memset(&decay, 0, sizeof(decay));
 
-	do_epoch();
-	sz = sizeof(uint64_t);
-	npurge1 = get_arena_npurge(0);
+	nstime_t curtime;
+	nstime_init(&curtime, 0);
 
-	if (config_stats) {
-		assert_u64_eq(npurge0, npurge1, "Unexpected purging occurred");
-	}
+	uint64_t decay_ms = 1000;
+	uint64_t decay_ns = decay_ms * 1000 * 1000;
 
-	nstime_monotonic = nstime_monotonic_orig;
-	nstime_update = nstime_update_orig;
-#undef NPS
-}
-TEST_END
+	bool err = decay_init(&decay, &curtime, (ssize_t)decay_ms);
+	assert_false(err, "");
 
-TEST_BEGIN(test_decay_now) {
-	test_skip_if(check_background_thread_enabled());
-
-	unsigned arena_ind = do_arena_create(0, 0);
-	assert_zu_eq(get_arena_pdirty(arena_ind), 0, "Unexpected dirty pages");
-	assert_zu_eq(get_arena_pmuzzy(arena_ind), 0, "Unexpected muzzy pages");
-	size_t sizes[] = {16, PAGE<<2, HUGEPAGE<<2};
-	/* Verify that dirty/muzzy pages never linger after deallocation. */
-	for (unsigned i = 0; i < sizeof(sizes)/sizeof(size_t); i++) {
-		size_t size = sizes[i];
-		generate_dirty(arena_ind, size);
-		assert_zu_eq(get_arena_pdirty(arena_ind), 0,
-		    "Unexpected dirty pages");
-		assert_zu_eq(get_arena_pmuzzy(arena_ind), 0,
-		    "Unexpected muzzy pages");
-	}
-	do_arena_destroy(arena_ind);
-}
-TEST_END
+	nstime_t epochtime;
+	nstime_init(&epochtime, decay_epoch_duration_ns(&decay));
 
-TEST_BEGIN(test_decay_never) {
-	test_skip_if(check_background_thread_enabled() || !config_stats);
-
-	unsigned arena_ind = do_arena_create(-1, -1);
-	int flags = MALLOCX_ARENA(arena_ind) | MALLOCX_TCACHE_NONE;
-	assert_zu_eq(get_arena_pdirty(arena_ind), 0, "Unexpected dirty pages");
-	assert_zu_eq(get_arena_pmuzzy(arena_ind), 0, "Unexpected muzzy pages");
-	size_t sizes[] = {16, PAGE<<2, HUGEPAGE<<2};
-	void *ptrs[sizeof(sizes)/sizeof(size_t)];
-	for (unsigned i = 0; i < sizeof(sizes)/sizeof(size_t); i++) {
-		ptrs[i] = do_mallocx(sizes[i], flags);
-	}
-	/* Verify that each deallocation generates additional dirty pages. */
-	size_t pdirty_prev = get_arena_pdirty(arena_ind);
-	size_t pmuzzy_prev = get_arena_pmuzzy(arena_ind);
-	assert_zu_eq(pdirty_prev, 0, "Unexpected dirty pages");
-	assert_zu_eq(pmuzzy_prev, 0, "Unexpected muzzy pages");
-	for (unsigned i = 0; i < sizeof(sizes)/sizeof(size_t); i++) {
-		dallocx(ptrs[i], flags);
-		size_t pdirty = get_arena_pdirty(arena_ind);
-		size_t pmuzzy = get_arena_pmuzzy(arena_ind);
-		assert_zu_gt(pdirty + (size_t)get_arena_dirty_purged(arena_ind),
-		    pdirty_prev, "Expected dirty pages to increase.");
-		assert_zu_eq(pmuzzy, 0, "Unexpected muzzy pages");
-		pdirty_prev = pdirty;
+	uint64_t ns_until_purge_empty = decay_ns_until_purge(&decay, 0, 0);
+	expect_u64_eq(ns_until_purge_empty, DECAY_UNBOUNDED_TIME_TO_PURGE,
+	    "Failed to return unbounded wait time for zero threshold");
+
+	const size_t dirty_pages_per_epoch = 1000;
+	size_t dirty_pages = 0;
+	bool epoch_advanced = false;
+	for (uint64_t i = 0; i < nepoch_init; i++) {
+		nstime_add(&curtime, &epochtime);
+		dirty_pages += dirty_pages_per_epoch;
+		epoch_advanced |= decay_maybe_advance_epoch(&decay, &curtime,
+		    dirty_pages);
 	}
-	do_arena_destroy(arena_ind);
+	expect_true(epoch_advanced, "Epoch never advanced");
+
+	uint64_t ns_until_purge_all = decay_ns_until_purge(&decay,
+	    dirty_pages, dirty_pages);
+	expect_u64_ge(ns_until_purge_all, decay_ns,
+	    "Incorrectly calculated time to purge all pages");
+
+	uint64_t ns_until_purge_none = decay_ns_until_purge(&decay,
+	    dirty_pages, 0);
+	expect_u64_eq(ns_until_purge_none, decay_epoch_duration_ns(&decay) * 2,
+	    "Incorrectly calculated time to purge 0 pages");
+
+	uint64_t npages_threshold = dirty_pages / 2;
+	uint64_t ns_until_purge_half = decay_ns_until_purge(&decay,
+	    dirty_pages, npages_threshold);
+
+	nstime_t waittime;
+	nstime_init(&waittime, ns_until_purge_half);
+	nstime_add(&curtime, &waittime);
+
+	decay_maybe_advance_epoch(&decay, &curtime, dirty_pages);
+	size_t npages_limit = decay_npages_limit_get(&decay);
+	expect_zu_lt(npages_limit, dirty_pages,
+	    "npages_limit failed to decrease after waiting");
+	size_t expected = dirty_pages - npages_limit;
+	int deviation = abs((int)expected - (int)(npages_threshold));
+	expect_d_lt(deviation, (int)(npages_threshold / 2),
+	    "After waiting, number of pages is out of the expected interval "
+	    "[0.5 * npages_threshold .. 1.5 * npages_threshold]");
 }
 TEST_END
 
 int
 main(void) {
 	return test(
-	    test_decay_ticks,
-	    test_decay_ticker,
-	    test_decay_nonmonotonic,
-	    test_decay_now,
-	    test_decay_never);
+	    test_decay_init,
+	    test_decay_ms_valid,
+	    test_decay_npages_purge_in,
+	    test_decay_maybe_advance_epoch,
+	    test_decay_empty,
+	    test_decay,
+	    test_decay_ns_until_purge);
 }