Implement guard pages.

Adding guarded extents, which are regular extents surrounded by guard pages
(mprotected).  To reduce syscalls, small guarded extents are cached as a
separate eset in ecache, and decay through the dirty / muzzy / retained pipeline
as usual.

test/include/test/arena_decay.h

@@ -0,0 +1,149 @@
+static unsigned
+do_arena_create(ssize_t dirty_decay_ms, ssize_t muzzy_decay_ms) {
+	unsigned arena_ind;
+	size_t sz = sizeof(unsigned);
+	expect_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);
+
+	expect_d_eq(mallctlnametomib("arena.0.dirty_decay_ms", mib, &miblen),
+	    0, "Unexpected mallctlnametomib() failure");
+	mib[1] = (size_t)arena_ind;
+	expect_d_eq(mallctlbymib(mib, miblen, NULL, NULL,
+	    (void *)&dirty_decay_ms, sizeof(dirty_decay_ms)), 0,
+	    "Unexpected mallctlbymib() failure");
+
+	expect_d_eq(mallctlnametomib("arena.0.muzzy_decay_ms", mib, &miblen),
+	    0, "Unexpected mallctlnametomib() failure");
+	mib[1] = (size_t)arena_ind;
+	expect_d_eq(mallctlbymib(mib, miblen, NULL, NULL,
+	    (void *)&muzzy_decay_ms, sizeof(muzzy_decay_ms)), 0,
+	    "Unexpected mallctlbymib() failure");
+
+	return arena_ind;
+}
+
+static void
+do_arena_destroy(unsigned arena_ind) {
+	size_t mib[3];
+	size_t miblen = sizeof(mib)/sizeof(size_t);
+	expect_d_eq(mallctlnametomib("arena.0.destroy", mib, &miblen), 0,
+	    "Unexpected mallctlnametomib() failure");
+	mib[1] = (size_t)arena_ind;
+	expect_d_eq(mallctlbymib(mib, miblen, NULL, NULL, NULL, 0), 0,
+	    "Unexpected mallctlbymib() failure");
+}
+
+static void
+do_epoch(void) {
+	uint64_t epoch = 1;
+	expect_d_eq(mallctl("epoch", NULL, NULL, (void *)&epoch, sizeof(epoch)),
+	    0, "Unexpected mallctl() failure");
+}
+
+static void
+do_purge(unsigned arena_ind) {
+	size_t mib[3];
+	size_t miblen = sizeof(mib)/sizeof(size_t);
+	expect_d_eq(mallctlnametomib("arena.0.purge", mib, &miblen), 0,
+	    "Unexpected mallctlnametomib() failure");
+	mib[1] = (size_t)arena_ind;
+	expect_d_eq(mallctlbymib(mib, miblen, NULL, NULL, NULL, 0), 0,
+	    "Unexpected mallctlbymib() failure");
+}
+
+static void
+do_decay(unsigned arena_ind) {
+	size_t mib[3];
+	size_t miblen = sizeof(mib)/sizeof(size_t);
+	expect_d_eq(mallctlnametomib("arena.0.decay", mib, &miblen), 0,
+	    "Unexpected mallctlnametomib() failure");
+	mib[1] = (size_t)arena_ind;
+	expect_d_eq(mallctlbymib(mib, miblen, NULL, NULL, NULL, 0), 0,
+	    "Unexpected mallctlbymib() failure");
+}
+
+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);
+	expect_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);
+	expect_d_eq(mallctlbymib(mib, miblen, (void *)&npurge, &sz, NULL, 0),
+	    config_stats ? 0 : ENOENT, "Unexpected mallctlbymib() failure");
+	return npurge;
+}
+
+static uint64_t
+get_arena_dirty_npurge(unsigned arena_ind) {
+	do_epoch();
+	return get_arena_npurge_impl("stats.arenas.0.dirty_npurge", arena_ind);
+}
+
+static uint64_t
+get_arena_dirty_purged(unsigned arena_ind) {
+	do_epoch();
+	return get_arena_npurge_impl("stats.arenas.0.dirty_purged", arena_ind);
+}
+
+static uint64_t
+get_arena_muzzy_npurge(unsigned arena_ind) {
+	do_epoch();
+	return get_arena_npurge_impl("stats.arenas.0.muzzy_npurge", arena_ind);
+}
+
+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);
+}
+
+static size_t
+get_arena_pdirty(unsigned arena_ind) {
+	do_epoch();
+	size_t mib[4];
+	size_t miblen = sizeof(mib)/sizeof(size_t);
+	expect_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);
+	expect_d_eq(mallctlbymib(mib, miblen, (void *)&pdirty, &sz, NULL, 0), 0,
+	    "Unexpected mallctlbymib() failure");
+	return pdirty;
+}
+
+static size_t
+get_arena_pmuzzy(unsigned arena_ind) {
+	do_epoch();
+	size_t mib[4];
+	size_t miblen = sizeof(mib)/sizeof(size_t);
+	expect_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);
+	expect_d_eq(mallctlbymib(mib, miblen, (void *)&pmuzzy, &sz, NULL, 0), 0,
+	    "Unexpected mallctlbymib() failure");
+	return pmuzzy;
+}
+
+static void *
+do_mallocx(size_t size, int flags) {
+	void *p = mallocx(size, flags);
+	expect_ptr_not_null(p, "Unexpected mallocx() failure");
+	return p;
+}
+
+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);
+}
+

test/include/test/guard.h

@@ -0,0 +1,6 @@
+static inline bool
+extent_is_guarded(tsdn_t *tsdn, void *ptr) {
+	edata_t *edata = emap_edata_lookup(tsdn, &arena_emap_global, ptr);
+	return edata_guarded_get(edata);
+}
+