San: Implement bump alloc

The new allocator will be used to allocate guarded extents used as slabs
for guarded small allocations.

15 files changed, 521 insertions, 107 deletions

diff --git a/Makefile.in b/Makefile.in
index 8f96a99..50c586c 100644
--- a/Makefile.in
+++ b/Makefile.in
@@ -120,6 +120,7 @@ C_SRCS := $(srcroot)src/jemalloc.c \
 	$(srcroot)src/extent_mmap.c \
 	$(srcroot)src/fxp.c \
 	$(srcroot)src/san.c \
+	$(srcroot)src/san_bump.c \
 	$(srcroot)src/hook.c \
 	$(srcroot)src/hpa.c \
 	$(srcroot)src/hpa_hooks.c \
@@ -220,6 +221,7 @@ TESTS_UNIT := \
 	$(srcroot)test/unit/fork.c \
 	${srcroot}test/unit/fxp.c \
 	${srcroot}test/unit/san.c \
+	${srcroot}test/unit/san_bump.c \
 	$(srcroot)test/unit/hash.c \
 	$(srcroot)test/unit/hook.c \
 	$(srcroot)test/unit/hpa.c \
diff --git a/include/jemalloc/internal/extent.h b/include/jemalloc/internal/extent.h
index 73c5563..73059ad 100644
--- a/include/jemalloc/internal/extent.h
+++ b/include/jemalloc/internal/extent.h
@@ -30,14 +30,20 @@ void ecache_dalloc(tsdn_t *tsdn, pac_t *pac, ehooks_t *ehooks,
 edata_t *ecache_evict(tsdn_t *tsdn, pac_t *pac, ehooks_t *ehooks,
     ecache_t *ecache, size_t npages_min);
 
+void extent_gdump_add(tsdn_t *tsdn, const edata_t *edata);
+void extent_record(tsdn_t *tsdn, pac_t *pac, ehooks_t *ehooks, ecache_t *ecache,
+    edata_t *edata);
 void extent_dalloc_gap(tsdn_t *tsdn, pac_t *pac, ehooks_t *ehooks,
     edata_t *edata);
+edata_t *extent_alloc_wrapper(tsdn_t *tsdn, pac_t *pac, ehooks_t *ehooks,
+    void *new_addr, size_t size, size_t alignment, bool zero, bool *commit,
+    bool growing_retained);
 void extent_dalloc_wrapper(tsdn_t *tsdn, pac_t *pac, ehooks_t *ehooks,
     edata_t *edata);
 void extent_destroy_wrapper(tsdn_t *tsdn, pac_t *pac, ehooks_t *ehooks,
     edata_t *edata);
 bool extent_commit_wrapper(tsdn_t *tsdn, ehooks_t *ehooks, edata_t *edata,
-    size_t offset, size_t length);
+    size_t offset, size_t length, bool growing_retained);
 bool extent_decommit_wrapper(tsdn_t *tsdn, ehooks_t *ehooks, edata_t *edata,
     size_t offset, size_t length);
 bool extent_purge_lazy_wrapper(tsdn_t *tsdn, ehooks_t *ehooks, edata_t *edata,
@@ -45,7 +51,8 @@ bool extent_purge_lazy_wrapper(tsdn_t *tsdn, ehooks_t *ehooks, edata_t *edata,
 bool extent_purge_forced_wrapper(tsdn_t *tsdn, ehooks_t *ehooks, edata_t *edata,
     size_t offset, size_t length);
 edata_t *extent_split_wrapper(tsdn_t *tsdn, pac_t *pac,
-    ehooks_t *ehooks, edata_t *edata, size_t size_a, size_t size_b);
+    ehooks_t *ehooks, edata_t *edata, size_t size_a, size_t size_b,
+    bool holding_core_locks);
 bool extent_merge_wrapper(tsdn_t *tsdn, pac_t *pac, ehooks_t *ehooks,
     edata_t *a, edata_t *b);
 size_t extent_sn_next(pac_t *pac);
diff --git a/include/jemalloc/internal/pac.h b/include/jemalloc/internal/pac.h
index 5eee3de..7eaaf89 100644
--- a/include/jemalloc/internal/pac.h
+++ b/include/jemalloc/internal/pac.h
@@ -3,6 +3,7 @@
 
 #include "jemalloc/internal/exp_grow.h"
 #include "jemalloc/internal/pai.h"
+#include "san_bump.h"
 
 
 /*
@@ -127,6 +128,11 @@ pac_mapped(pac_t *pac) {
 	return atomic_load_zu(&pac->stats->pac_mapped, ATOMIC_RELAXED);
 }
 
+static inline ehooks_t *
+pac_ehooks_get(pac_t *pac) {
+	return base_ehooks_get(pac->base);
+}
+
 /*
  * All purging functions require holding decay->mtx.  This is one of the few
  * places external modules are allowed to peek inside pa_shard_t internals.
diff --git a/include/jemalloc/internal/san.h b/include/jemalloc/internal/san.h
index b3d0304..70debf3 100644
--- a/include/jemalloc/internal/san.h
+++ b/include/jemalloc/internal/san.h
@@ -4,7 +4,8 @@
 #include "jemalloc/internal/ehooks.h"
 #include "jemalloc/internal/emap.h"
 
-#define PAGE_GUARDS_SIZE (2 * PAGE)
+#define SAN_PAGE_GUARD PAGE
+#define SAN_PAGE_GUARDS_SIZE (SAN_PAGE_GUARD * 2)
 
 #define SAN_GUARD_LARGE_EVERY_N_EXTENTS_DEFAULT 0
 #define SAN_GUARD_SMALL_EVERY_N_EXTENTS_DEFAULT 0
@@ -14,9 +15,9 @@ extern size_t opt_san_guard_large;
 extern size_t opt_san_guard_small;
 
 void san_guard_pages(tsdn_t *tsdn, ehooks_t *ehooks, edata_t *edata,
-    emap_t *emap);
+    emap_t *emap, bool left, bool right, bool remap);
 void san_unguard_pages(tsdn_t *tsdn, ehooks_t *ehooks, edata_t *edata,
-    emap_t *emap);
+    emap_t *emap, bool left, bool right);
 /*
  * Unguard the extent, but don't modify emap boundaries. Must be called on an
  * extent that has been erased from emap and shouldn't be placed back.
@@ -25,6 +26,45 @@ void san_unguard_pages_pre_destroy(tsdn_t *tsdn, ehooks_t *ehooks,
     edata_t *edata, emap_t *emap);
 void tsd_san_init(tsd_t *tsd);
 
+static inline void
+san_guard_pages_two_sided(tsdn_t *tsdn, ehooks_t *ehooks, edata_t *edata,
+    emap_t *emap, bool remap) {
+	return san_guard_pages(tsdn, ehooks, edata, emap, true, true,
+	    remap);
+}
+
+static inline void
+san_unguard_pages_two_sided(tsdn_t *tsdn, ehooks_t *ehooks, edata_t *edata,
+    emap_t *emap) {
+	return san_unguard_pages(tsdn, ehooks, edata, emap, true, true);
+}
+
+static inline size_t
+san_two_side_unguarded_sz(size_t size) {
+	assert(size % PAGE == 0);
+	assert(size >= SAN_PAGE_GUARDS_SIZE);
+	return size - SAN_PAGE_GUARDS_SIZE;
+}
+
+static inline size_t
+san_two_side_guarded_sz(size_t size) {
+	assert(size % PAGE == 0);
+	return size + SAN_PAGE_GUARDS_SIZE;
+}
+
+static inline size_t
+san_one_side_unguarded_sz(size_t size) {
+	assert(size % PAGE == 0);
+	assert(size >= SAN_PAGE_GUARD);
+	return size - SAN_PAGE_GUARD;
+}
+
+static inline size_t
+san_one_side_guarded_sz(size_t size) {
+	assert(size % PAGE == 0);
+	return size + SAN_PAGE_GUARD;
+}
+
 static inline bool
 san_enabled(void) {
 	return (opt_san_guard_large != 0 || opt_san_guard_small != 0);
@@ -50,7 +90,7 @@ san_large_extent_decide_guard(tsdn_t *tsdn, ehooks_t *ehooks, size_t size,
 	}
 
 	if (n == 1 && (alignment <= PAGE) &&
-	    (size + PAGE_GUARDS_SIZE <= SC_LARGE_MAXCLASS)) {
+	    (san_two_side_guarded_sz(size) <= SC_LARGE_MAXCLASS)) {
 		*tsd_san_extents_until_guard_largep_get(tsd) =
 		    opt_san_guard_large;
 		return true;
diff --git a/include/jemalloc/internal/san_bump.h b/include/jemalloc/internal/san_bump.h
new file mode 100644
index 0000000..9c6c224
--- /dev/null
+++ b/include/jemalloc/internal/san_bump.h
@@ -0,0 +1,27 @@
+#ifndef JEMALLOC_INTERNAL_SAN_BUMP_H
+#define JEMALLOC_INTERNAL_SAN_BUMP_H
+
+#include "jemalloc/internal/edata.h"
+#include "jemalloc/internal/exp_grow.h"
+#include "jemalloc/internal/mutex.h"
+
+extern const size_t SBA_RETAINED_ALLOC_SIZE;
+
+typedef struct ehooks_s ehooks_t;
+typedef struct pac_s pac_t;
+
+typedef struct san_bump_alloc_s san_bump_alloc_t;
+struct san_bump_alloc_s {
+	malloc_mutex_t mtx;
+
+	edata_t *curr_reg;
+};
+
+bool
+san_bump_alloc_init(san_bump_alloc_t* sba);
+
+edata_t *
+san_bump_alloc(tsdn_t *tsdn, san_bump_alloc_t* sba, pac_t *pac, ehooks_t *ehooks,
+    size_t size, bool zero);
+
+#endif /* JEMALLOC_INTERNAL_SAN_BUMP_H */
diff --git a/include/jemalloc/internal/witness.h b/include/jemalloc/internal/witness.h
index c12a705..e81b9a0 100644
--- a/include/jemalloc/internal/witness.h
+++ b/include/jemalloc/internal/witness.h
@@ -48,6 +48,7 @@ enum witness_rank_e {
 
 	WITNESS_RANK_EXTENT_GROW,
 	WITNESS_RANK_HPA_SHARD_GROW = WITNESS_RANK_EXTENT_GROW,
+	WITNESS_RANK_SAN_BUMP_ALLOC = WITNESS_RANK_EXTENT_GROW,
 
 	WITNESS_RANK_EXTENTS,
 	WITNESS_RANK_HPA_SHARD = WITNESS_RANK_EXTENTS,
diff --git a/src/extent.c b/src/extent.c
index 7112d3a..13d688d 100644
--- a/src/extent.c
+++ b/src/extent.c
@@ -40,13 +40,9 @@ static edata_t *extent_recycle(tsdn_t *tsdn, pac_t *pac, ehooks_t *ehooks,
     bool zero, bool *commit, bool growing_retained, bool guarded);
 static edata_t *extent_try_coalesce(tsdn_t *tsdn, pac_t *pac, ehooks_t *ehooks,
     ecache_t *ecache, edata_t *edata, bool *coalesced);
-static void extent_record(tsdn_t *tsdn, pac_t *pac, ehooks_t *ehooks,
-    ecache_t *ecache, edata_t *edata);
 static edata_t *extent_alloc_retained(tsdn_t *tsdn, pac_t *pac,
     ehooks_t *ehooks, edata_t *expand_edata, size_t size, size_t alignment,
     bool zero, bool *commit, bool guarded);
-static edata_t *extent_alloc_wrapper(tsdn_t *tsdn, pac_t *pac, ehooks_t *ehooks,
-    void *new_addr, size_t size, size_t alignment, bool zero, bool *commit);
 
 /******************************************************************************/
 
@@ -127,7 +123,8 @@ ecache_alloc_grow(tsdn_t *tsdn, pac_t *pac, ehooks_t *ehooks, ecache_t *ecache,
 		void *new_addr = (expand_edata == NULL) ? NULL :
 		    edata_past_get(expand_edata);
 		edata = extent_alloc_wrapper(tsdn, pac, ehooks, new_addr,
-		    size, alignment, zero, &commit);
+		    size, alignment, zero, &commit,
+		    /* growing_retained */ false);
 	}
 
 	assert(edata == NULL || edata_pai_get(edata) == EXTENT_PAI_PAC);
@@ -270,7 +267,7 @@ extent_activate_locked(tsdn_t *tsdn, pac_t *pac, ecache_t *ecache, eset_t *eset,
 	emap_update_edata_state(tsdn, pac->emap, edata, extent_state_active);
 }
 
-static void
+void
 extent_gdump_add(tsdn_t *tsdn, const edata_t *edata) {
 	cassert(config_prof);
 	/* prof_gdump() requirement. */
@@ -785,35 +782,6 @@ extent_alloc_retained(tsdn_t *tsdn, pac_t *pac, ehooks_t *ehooks,
 	return edata;
 }
 
-static edata_t *
-extent_alloc_wrapper(tsdn_t *tsdn, pac_t *pac, ehooks_t *ehooks,
-    void *new_addr, size_t size, size_t alignment, bool zero, bool *commit) {
-	witness_assert_depth_to_rank(tsdn_witness_tsdp_get(tsdn),
-	    WITNESS_RANK_CORE, 0);
-
-	edata_t *edata = edata_cache_get(tsdn, pac->edata_cache);
-	if (edata == NULL) {
-		return NULL;
-	}
-	size_t palignment = ALIGNMENT_CEILING(alignment, PAGE);
-	void *addr = ehooks_alloc(tsdn, ehooks, new_addr, size, palignment,
-	    &zero, commit);
-	if (addr == NULL) {
-		edata_cache_put(tsdn, pac->edata_cache, edata);
-		return NULL;
-	}
-	edata_init(edata, ecache_ind_get(&pac->ecache_dirty), addr,
-	    size, /* slab */ false, SC_NSIZES, extent_sn_next(pac),
-	    extent_state_active, zero, *commit, EXTENT_PAI_PAC,
-	    opt_retain ? EXTENT_IS_HEAD : EXTENT_NOT_HEAD);
-	if (extent_register(tsdn, pac, edata)) {
-		edata_cache_put(tsdn, pac->edata_cache, edata);
-		return NULL;
-	}
-
-	return edata;
-}
-
 static bool
 extent_coalesce(tsdn_t *tsdn, pac_t *pac, ehooks_t *ehooks, ecache_t *ecache,
     edata_t *inner, edata_t *outer, bool forward) {
@@ -924,9 +892,9 @@ extent_maximally_purge(tsdn_t *tsdn, pac_t *pac, ehooks_t *ehooks,
  * Does the metadata management portions of putting an unused extent into the
  * given ecache_t (coalesces and inserts into the eset).
  */
-static void
-extent_record(tsdn_t *tsdn, pac_t *pac, ehooks_t *ehooks,
-    ecache_t *ecache, edata_t *edata) {
+void
+extent_record(tsdn_t *tsdn, pac_t *pac, ehooks_t *ehooks, ecache_t *ecache,
+    edata_t *edata) {
 	assert((ecache->state != extent_state_dirty &&
 	    ecache->state != extent_state_muzzy) ||
 	    !edata_zeroed_get(edata));
@@ -1001,6 +969,42 @@ extent_dalloc_wrapper_try(tsdn_t *tsdn, pac_t *pac, ehooks_t *ehooks,
 	return err;
 }
 
+edata_t *
+extent_alloc_wrapper(tsdn_t *tsdn, pac_t *pac, ehooks_t *ehooks,
+    void *new_addr, size_t size, size_t alignment, bool zero, bool *commit,
+    bool growing_retained) {
+	witness_assert_depth_to_rank(tsdn_witness_tsdp_get(tsdn),
+	    WITNESS_RANK_CORE, growing_retained ? 1 : 0);
+
+	edata_t *edata = edata_cache_get(tsdn, pac->edata_cache);
+	if (edata == NULL) {
+		return NULL;
+	}
+	size_t palignment = ALIGNMENT_CEILING(alignment, PAGE);
+	void *addr = ehooks_alloc(tsdn, ehooks, new_addr, size, palignment,
+	    &zero, commit);
+	if (addr == NULL) {
+		edata_cache_put(tsdn, pac->edata_cache, edata);
+		return NULL;
+	}
+	edata_init(edata, ecache_ind_get(&pac->ecache_dirty), addr,
+	    size, /* slab */ false, SC_NSIZES, extent_sn_next(pac),
+	    extent_state_active, zero, *commit, EXTENT_PAI_PAC,
+	    opt_retain ? EXTENT_IS_HEAD : EXTENT_NOT_HEAD);
+	/*
+	 * Retained memory is not counted towards gdump.  Only if an extent is
+	 * allocated as a separate mapping, i.e. growing_retained is false, then
+	 * gdump should be updated.
+	 */
+	bool gdump_add = !growing_retained;
+	if (extent_register_impl(tsdn, pac, edata, gdump_add)) {
+		edata_cache_put(tsdn, pac->edata_cache, edata);
+		return NULL;
+	}
+
+	return edata;
+}
+
 void
 extent_dalloc_wrapper(tsdn_t *tsdn, pac_t *pac, ehooks_t *ehooks,
     edata_t *edata) {
@@ -1013,7 +1017,8 @@ extent_dalloc_wrapper(tsdn_t *tsdn, pac_t *pac, ehooks_t *ehooks,
 		/* Restore guard pages for dalloc / unmap. */
 		if (edata_guarded_get(edata)) {
 			assert(ehooks_are_default(ehooks));
-			san_unguard_pages(tsdn, ehooks, edata, pac->emap);
+			san_unguard_pages_two_sided(tsdn, ehooks, edata,
+			    pac->emap);
 		}
 		/*
 		 * Deregister first to avoid a race with other allocating
@@ -1057,12 +1062,14 @@ extent_destroy_wrapper(tsdn_t *tsdn, pac_t *pac, ehooks_t *ehooks,
     edata_t *edata) {
 	assert(edata_base_get(edata) != NULL);
 	assert(edata_size_get(edata) != 0);
-	assert(edata_state_get(edata) == extent_state_retained);
+	extent_state_t state = edata_state_get(edata);
+	assert(state == extent_state_retained || state == extent_state_active);
 	assert(emap_edata_is_acquired(tsdn, pac->emap, edata));
 	witness_assert_depth_to_rank(tsdn_witness_tsdp_get(tsdn),
 	    WITNESS_RANK_CORE, 0);
 
 	if (edata_guarded_get(edata)) {
+		assert(opt_retain);
 		san_unguard_pages_pre_destroy(tsdn, ehooks, edata, pac->emap);
 	}
 	edata_addr_set(edata, edata_base_get(edata));
@@ -1087,9 +1094,9 @@ extent_commit_impl(tsdn_t *tsdn, ehooks_t *ehooks, edata_t *edata,
 
 bool
 extent_commit_wrapper(tsdn_t *tsdn, ehooks_t *ehooks, edata_t *edata,
-    size_t offset, size_t length) {
+    size_t offset, size_t length, bool growing_retained) {
 	return extent_commit_impl(tsdn, ehooks, edata, offset, length,
-	    false);
+	    growing_retained);
 }
 
 bool
@@ -1207,9 +1214,9 @@ label_error_a:
 
 edata_t *
 extent_split_wrapper(tsdn_t *tsdn, pac_t *pac, ehooks_t *ehooks, edata_t *edata,
-    size_t size_a, size_t size_b) {
+    size_t size_a, size_t size_b, bool holding_core_locks) {
 	return extent_split_impl(tsdn, pac, ehooks, edata, size_a, size_b,
-	    /* holding_core_locks */ false);
+	    holding_core_locks);
 }
 
 static bool
diff --git a/src/pac.c b/src/pac.c
index e53de80..914cec9 100644
--- a/src/pac.c
+++ b/src/pac.c
@@ -14,11 +14,6 @@ static void pac_dalloc_impl(tsdn_t *tsdn, pai_t *self, edata_t *edata,
     bool *deferred_work_generated);
 static uint64_t pac_time_until_deferred_work(tsdn_t *tsdn, pai_t *self);
 
-static ehooks_t *
-pac_ehooks_get(pac_t *pac) {
-	return base_ehooks_get(pac->base);
-}
-
 static inline void
 pac_decay_data_get(pac_t *pac, extent_state_t state,
     decay_t **r_decay, pac_decay_stats_t **r_decay_stats, ecache_t **r_ecache) {
@@ -139,14 +134,15 @@ pac_alloc_new_guarded(tsdn_t *tsdn, pac_t *pac, ehooks_t *ehooks, size_t size,
     size_t alignment, bool zero) {
 	assert(alignment <= PAGE);
 
-	size_t size_with_guards = size + PAGE_GUARDS_SIZE;
+	size_t size_with_guards = size + SAN_PAGE_GUARDS_SIZE;
 	/* Alloc a non-guarded extent first.*/
 	edata_t *edata = pac_alloc_real(tsdn, pac, ehooks, size_with_guards,
 	    /* alignment */ PAGE, zero, /* guarded */ false);
 	if (edata != NULL) {
 		/* Add guards around it. */
 		assert(edata_size_get(edata) == size_with_guards);
-		san_guard_pages(tsdn, ehooks, edata, pac->emap);
+		san_guard_pages(tsdn, ehooks, edata, pac->emap, true, true,
+		    true);
 	}
 	assert(edata == NULL || (edata_guarded_get(edata) &&
 	    edata_size_get(edata) == size));
@@ -222,7 +218,7 @@ pac_shrink_impl(tsdn_t *tsdn, pai_t *self, edata_t *edata, size_t old_size,
 	}
 
 	edata_t *trail = extent_split_wrapper(tsdn, pac, ehooks, edata,
-	    new_size, shrink_amount);
+	    new_size, shrink_amount, /* holding_core_locks */ false);
 	if (trail == NULL) {
 		return true;
 	}
@@ -253,7 +249,8 @@ pac_dalloc_impl(tsdn_t *tsdn, pai_t *self, edata_t *edata,
 		if (!edata_slab_get(edata) || !maps_coalesce) {
 			assert(edata_size_get(edata) >= SC_LARGE_MINCLASS ||
 			    !maps_coalesce);
-			san_unguard_pages(tsdn, ehooks, edata, pac->emap);
+			san_unguard_pages_two_sided(tsdn, ehooks, edata,
+			    pac->emap);
 		}
 	}
 
diff --git a/src/pages.c b/src/pages.c
index a8d9988..8c83a7d 100644
--- a/src/pages.c
+++ b/src/pages.c
@@ -365,33 +365,61 @@ pages_decommit(void *addr, size_t size) {
 
 void
 pages_mark_guards(void *head, void *tail) {
-	assert(head != NULL && tail != NULL);
-	assert((uintptr_t)head < (uintptr_t)tail);
+	assert(head != NULL || tail != NULL);
+	assert(head == NULL || tail == NULL ||
+	    (uintptr_t)head < (uintptr_t)tail);
 #ifdef JEMALLOC_HAVE_MPROTECT
-	mprotect(head, PAGE, PROT_NONE);
-	mprotect(tail, PAGE, PROT_NONE);
+	if (head != NULL) {
+		mprotect(head, PAGE, PROT_NONE);
+	}
+	if (tail != NULL) {
+		mprotect(tail, PAGE, PROT_NONE);
+	}
 #else
 	/* Decommit sets to PROT_NONE / MEM_DECOMMIT. */
-	os_pages_commit(head, PAGE, false);
-	os_pages_commit(tail, PAGE, false);
+	if (head != NULL) {
+		os_pages_commit(head, PAGE, false);
+	}
+	if (tail != NULL) {
+		os_pages_commit(tail, PAGE, false);
+	}
 #endif
 }
 
 void
 pages_unmark_guards(void *head, void *tail) {
-	assert(head != NULL && tail != NULL);
-	assert((uintptr_t)head < (uintptr_t)tail);
+	assert(head != NULL || tail != NULL);
+	assert(head == NULL || tail == NULL ||
+	    (uintptr_t)head < (uintptr_t)tail);
 #ifdef JEMALLOC_HAVE_MPROTECT
-	size_t range = (uintptr_t)tail - (uintptr_t)head + PAGE;
-	if (range <= SC_LARGE_MINCLASS) {
+	bool head_and_tail = (head != NULL) && (tail != NULL);
+	size_t range = head_and_tail ?
+	    (uintptr_t)tail - (uintptr_t)head + PAGE :
+	    SIZE_T_MAX;
+	/*
+	 * The amount of work that the kernel does in mprotect depends on the
+	 * range argument.  SC_LARGE_MINCLASS is an arbitrary threshold chosen
+	 * to prevent kernel from doing too much work that would outweigh the
+	 * savings of performing one less system call.
+	 */
+	bool ranged_mprotect = head_and_tail && range <= SC_LARGE_MINCLASS;
+	if (ranged_mprotect) {
 		mprotect(head, range, PROT_READ | PROT_WRITE);
 	} else {
-		mprotect(head, PAGE, PROT_READ | PROT_WRITE);
-		mprotect(tail, PAGE, PROT_READ | PROT_WRITE);
+		if (head != NULL) {
+			mprotect(head, PAGE, PROT_READ | PROT_WRITE);
+		}
+		if (tail != NULL) {
+			mprotect(tail, PAGE, PROT_READ | PROT_WRITE);
+		}
 	}
 #else
-	os_pages_commit(head, PAGE, true);
-	os_pages_commit(tail, PAGE, true);
+	if (head != NULL) {
+		os_pages_commit(head, PAGE, true);
+	}
+	if (tail != NULL) {
+		os_pages_commit(tail, PAGE, true);
+	}
 #endif
 }
 
diff --git a/src/san.c b/src/san.c
index 139ec5a..15fdb7f 100644
--- a/src/san.c
+++ b/src/san.c
@@ -10,16 +10,63 @@
 size_t opt_san_guard_large = SAN_GUARD_LARGE_EVERY_N_EXTENTS_DEFAULT;
 size_t opt_san_guard_small = SAN_GUARD_SMALL_EVERY_N_EXTENTS_DEFAULT;
 
+static inline void
+san_find_guarded_addr(edata_t *edata, uintptr_t *guard1, uintptr_t *guard2,
+    uintptr_t *addr, size_t size, bool left, bool right) {
+	assert(!edata_guarded_get(edata));
+	assert(size % PAGE == 0);
+	*addr = (uintptr_t)edata_base_get(edata);
+	if (left) {
+		*guard1 = *addr;
+		*addr += SAN_PAGE_GUARD;
+	} else {
+		*guard1 = 0;
+	}
+
+	if (right) {
+		*guard2 = *addr + size;
+	} else {
+		*guard2 = 0;
+	}
+}
+
+static inline void
+san_find_unguarded_addr(edata_t *edata, uintptr_t *guard1, uintptr_t *guard2,
+    uintptr_t *addr, size_t size, bool left, bool right) {
+	assert(edata_guarded_get(edata));
+	assert(size % PAGE == 0);
+	*addr = (uintptr_t)edata_base_get(edata);
+	if (right) {
+		*guard2 = *addr + size;
+	} else {
+		*guard2 = 0;
+	}
+
+	if (left) {
+		*guard1 = *addr - SAN_PAGE_GUARD;
+		assert(*guard1 != 0);
+		*addr = *guard1;
+	} else {
+		*guard1 = 0;
+	}
+}
+
 void
-san_guard_pages(tsdn_t *tsdn, ehooks_t *ehooks, edata_t *edata, emap_t *emap) {
-	emap_deregister_boundary(tsdn, emap, edata);
+san_guard_pages(tsdn_t *tsdn, ehooks_t *ehooks, edata_t *edata, emap_t *emap,
+    bool left, bool right, bool remap) {
+	assert(left || right);
+	if (remap) {
+		emap_deregister_boundary(tsdn, emap, edata);
+	}
 
 	size_t size_with_guards = edata_size_get(edata);
-	size_t usize = size_with_guards - PAGE_GUARDS_SIZE;
+	size_t usize = (left && right)
+	    ? san_two_side_unguarded_sz(size_with_guards)
+	    : san_one_side_unguarded_sz(size_with_guards);
 
-	uintptr_t guard1 = (uintptr_t)edata_base_get(edata);
-	uintptr_t addr = guard1 + PAGE;
-	uintptr_t guard2 = addr + usize;
+	uintptr_t guard1, guard2, addr;
+	san_find_guarded_addr(edata, &guard1, &guard2, &addr, usize, left,
+	    right);
 
 	assert(edata_state_get(edata) == extent_state_active);
 	ehooks_guard(tsdn, ehooks, (void *)guard1, (void *)guard2);
@@ -29,14 +76,18 @@ san_guard_pages(tsdn_t *tsdn, ehooks_t *ehooks, edata_t *edata, emap_t *emap) {
 	edata_addr_set(edata, (void *)addr);
 	edata_guarded_set(edata, true);
 
-	/* The new boundary will be registered on the pa_alloc path. */
+	if (remap) {
+		emap_register_boundary(tsdn, emap, edata, SC_NSIZES,
+		    /* slab */ false);
+	}
 }
 
 static void
 san_unguard_pages_impl(tsdn_t *tsdn, ehooks_t *ehooks, edata_t *edata,
-    emap_t *emap, bool reg_emap) {
+    emap_t *emap, bool left, bool right, bool remap) {
+	assert(left || right);
 	/* Remove the inner boundary which no longer exists. */
-	if (reg_emap) {
+	if (remap) {
 		assert(edata_state_get(edata) == extent_state_active);
 		emap_deregister_boundary(tsdn, emap, edata);
 	} else {
@@ -44,24 +95,26 @@ san_unguard_pages_impl(tsdn_t *tsdn, ehooks_t *ehooks, edata_t *edata,
 	}
 
 	size_t size = edata_size_get(edata);
-	size_t size_with_guards = size + PAGE_GUARDS_SIZE;
+	size_t size_with_guards = (left && right)
+	    ? san_two_side_guarded_sz(size)
+	    : san_one_side_guarded_sz(size);
 
-	uintptr_t addr =  (uintptr_t)edata_base_get(edata);
-	uintptr_t guard1 = addr - PAGE;
-	uintptr_t guard2 = addr + size;
+	uintptr_t guard1, guard2, addr;
+	san_find_unguarded_addr(edata, &guard1, &guard2, &addr, size, left,
+	    right);
 
 	ehooks_unguard(tsdn, ehooks, (void *)guard1, (void *)guard2);
 
 	/* Update the true addr and usable size of the edata. */
 	edata_size_set(edata, size_with_guards);
-	edata_addr_set(edata, (void *)guard1);
+	edata_addr_set(edata, (void *)addr);
 	edata_guarded_set(edata, false);
 
 	/*
 	 * Then re-register the outer boundary including the guards, if
 	 * requested.
 	 */
-	if (reg_emap) {
+	if (remap) {
 		emap_register_boundary(tsdn, emap, edata, SC_NSIZES,
 		    /* slab */ false);
 	}
@@ -69,15 +122,23 @@ san_unguard_pages_impl(tsdn_t *tsdn, ehooks_t *ehooks, edata_t *edata,
 
 void
 san_unguard_pages(tsdn_t *tsdn, ehooks_t *ehooks, edata_t *edata,
-    emap_t *emap) {
-	san_unguard_pages_impl(tsdn, ehooks, edata, emap, /* reg_emap */ true);
+    emap_t *emap, bool left, bool right) {
+	san_unguard_pages_impl(tsdn, ehooks, edata, emap, left, right,
+	    /* remap */ true);
 }
 
 void
 san_unguard_pages_pre_destroy(tsdn_t *tsdn, ehooks_t *ehooks, edata_t *edata,
     emap_t *emap) {
 	emap_assert_not_mapped(tsdn, emap, edata);
-	san_unguard_pages_impl(tsdn, ehooks, edata, emap, /* reg_emap */ false);
+	/*
+	 * We don't want to touch the emap of about to be destroyed extents, as
+	 * they have been unmapped upon eviction from the retained ecache. Also,
+	 * we unguard the extents to the right, because retained extents only
+	 * own their right guard page per san_bump_alloc's logic.
+	 */
+	 san_unguard_pages_impl(tsdn, ehooks, edata, emap, /* left */ false,
+	    /* right */ true, /* remap */ false);
 }
 
 void
diff --git a/src/san_bump.c b/src/san_bump.c
new file mode 100644
index 0000000..6098bd9
--- /dev/null
+++ b/src/san_bump.c
@@ -0,0 +1,127 @@
+#include "jemalloc/internal/jemalloc_preamble.h"
+#include "jemalloc/internal/jemalloc_internal_includes.h"
+
+#include "jemalloc/internal/san_bump.h"
+#include "jemalloc/internal/pac.h"
+#include "jemalloc/internal/san.h"
+#include "jemalloc/internal/ehooks.h"
+#include "jemalloc/internal/edata_cache.h"
+
+const size_t SBA_RETAINED_ALLOC_SIZE = 1024 * 1024 * 4; /* 4 MB */
+
+static bool
+san_bump_grow_locked(tsdn_t *tsdn, san_bump_alloc_t *sba, pac_t *pac,
+    ehooks_t *ehooks, size_t size);
+
+bool
+san_bump_alloc_init(san_bump_alloc_t* sba) {
+	bool err = malloc_mutex_init(&sba->mtx, "sanitizer_bump_allocator",
+	    WITNESS_RANK_SAN_BUMP_ALLOC, malloc_mutex_rank_exclusive);
+	if (err) {
+		return true;
+	}
+	sba->curr_reg = NULL;
+
+	return false;
+}
+
+edata_t *
+san_bump_alloc(tsdn_t *tsdn, san_bump_alloc_t* sba, pac_t *pac,
+    ehooks_t *ehooks, size_t size, bool zero) {
+	assert(maps_coalesce && opt_retain);
+
+	edata_t* to_destroy;
+	size_t guarded_size = san_one_side_guarded_sz(size);
+
+	malloc_mutex_lock(tsdn, &sba->mtx);
+
+	if (sba->curr_reg == NULL ||
+	    edata_size_get(sba->curr_reg) < guarded_size) {
+		/*
+		 * If the current region can't accommodate the allocation,
+		 * try replacing it with a larger one and destroy current if the
+		 * replacement succeeds.
+		 */
+		to_destroy = sba->curr_reg;
+		bool err = san_bump_grow_locked(tsdn, sba, pac, ehooks,
+		    guarded_size);
+		if (err) {
+			goto label_err;
+		}
+	} else {
+		to_destroy = NULL;
+	}
+	assert(guarded_size <= edata_size_get(sba->curr_reg));
+	size_t trail_size = edata_size_get(sba->curr_reg) - guarded_size;
+
+	edata_t* edata;
+	if (trail_size != 0) {
+		edata_t* curr_reg_trail = extent_split_wrapper(tsdn, pac,
+		    ehooks, sba->curr_reg, guarded_size, trail_size,
+		    /* holding_core_locks */ true);
+		if (curr_reg_trail == NULL) {
+			goto label_err;
+		}
+		edata = sba->curr_reg;
+		sba->curr_reg = curr_reg_trail;
+	} else {
+		edata = sba->curr_reg;
+		sba->curr_reg = NULL;
+	}
+
+	malloc_mutex_unlock(tsdn, &sba->mtx);
+
+	assert(!edata_guarded_get(edata));
+	assert(sba->curr_reg == NULL || !edata_guarded_get(sba->curr_reg));
+	assert(to_destroy == NULL || !edata_guarded_get(to_destroy));
+
+	if (to_destroy != NULL) {
+		extent_destroy_wrapper(tsdn, pac, ehooks, to_destroy);
+	}
+
+	san_guard_pages(tsdn, ehooks, edata, pac->emap, /* left */ false,
+	    /* right */ true, /* remap */ true);
+
+	if (!edata_committed_get(edata)) {
+		if (extent_commit_wrapper(tsdn, ehooks, edata, 0,
+		    edata_size_get(edata), true)) {
+			extent_record(tsdn, pac, ehooks, &pac->ecache_retained,
+			    edata);
+			return NULL;
+		}
+		edata_committed_set(edata, true);
+	}
+	if (zero && !edata_zeroed_get(edata)) {
+		void *addr = edata_base_get(edata);
+		size_t size = edata_size_get(edata);
+		ehooks_zero(tsdn, ehooks, addr, size);
+		edata_zeroed_set(edata, true);
+	}
+
+	if (config_prof) {
+		extent_gdump_add(tsdn, edata);
+	}
+
+	return edata;
+label_err:
+	malloc_mutex_unlock(tsdn, &sba->mtx);
+	return NULL;
+}
+
+static bool
+san_bump_grow_locked(tsdn_t *tsdn, san_bump_alloc_t *sba, pac_t *pac,
+    ehooks_t *ehooks, size_t size) {
+	malloc_mutex_assert_owner(tsdn, &sba->mtx);
+
+	bool committed = false, zeroed = false;
+	size_t alloc_size = size > SBA_RETAINED_ALLOC_SIZE ? size :
+	    SBA_RETAINED_ALLOC_SIZE;
+	assert((alloc_size & PAGE_MASK) == 0);
+	sba->curr_reg = extent_alloc_wrapper(tsdn, pac, ehooks, NULL,
+	    alloc_size, PAGE, zeroed, &committed,
+	    /* growing_retained */ true);
+	if (sba->curr_reg == NULL) {
+		return true;
+	}
+	return false;
+}
diff --git a/test/include/test/arena_decay.h b/test/include/test/arena_decay.h
index da65921..524ee21 100644
--- a/test/include/test/arena_decay.h
+++ b/test/include/test/arena_decay.h
@@ -1,4 +1,4 @@
-static unsigned
+static inline unsigned
 do_arena_create(ssize_t dirty_decay_ms, ssize_t muzzy_decay_ms) {
 	unsigned arena_ind;
 	size_t sz = sizeof(unsigned);
@@ -24,7 +24,7 @@ do_arena_create(ssize_t dirty_decay_ms, ssize_t muzzy_decay_ms) {
 	return arena_ind;
 }
 
-static void
+static inline void
 do_arena_destroy(unsigned arena_ind) {
 	size_t mib[3];
 	size_t miblen = sizeof(mib)/sizeof(size_t);
@@ -35,14 +35,14 @@ do_arena_destroy(unsigned arena_ind) {
 	    "Unexpected mallctlbymib() failure");
 }
 
-static void
+static inline 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
+static inline void
 do_purge(unsigned arena_ind) {
 	size_t mib[3];
 	size_t miblen = sizeof(mib)/sizeof(size_t);
@@ -53,7 +53,7 @@ do_purge(unsigned arena_ind) {
 	    "Unexpected mallctlbymib() failure");
 }
 
-static void
+static inline void
 do_decay(unsigned arena_ind) {
 	size_t mib[3];
 	size_t miblen = sizeof(mib)/sizeof(size_t);
@@ -64,7 +64,7 @@ do_decay(unsigned arena_ind) {
 	    "Unexpected mallctlbymib() failure");
 }
 
-static uint64_t
+static inline uint64_t
 get_arena_npurge_impl(const char *mibname, unsigned arena_ind) {
 	size_t mib[4];
 	size_t miblen = sizeof(mib)/sizeof(size_t);
@@ -78,32 +78,32 @@ get_arena_npurge_impl(const char *mibname, unsigned arena_ind) {
 	return npurge;
 }
 
-static uint64_t
+static inline 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
+static inline 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
+static inline 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
+static inline 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
+static inline size_t
 get_arena_pdirty(unsigned arena_ind) {
 	do_epoch();
 	size_t mib[4];
@@ -118,7 +118,7 @@ get_arena_pdirty(unsigned arena_ind) {
 	return pdirty;
 }
 
-static size_t
+static inline size_t
 get_arena_pmuzzy(unsigned arena_ind) {
 	do_epoch();
 	size_t mib[4];
@@ -133,14 +133,14 @@ get_arena_pmuzzy(unsigned arena_ind) {
 	return pmuzzy;
 }
 
-static void *
+static inline 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
+static inline void
 generate_dirty(unsigned arena_ind, size_t size) {
 	int flags = MALLOCX_ARENA(arena_ind) | MALLOCX_TCACHE_NONE;
 	void *p = do_mallocx(size, flags);
diff --git a/test/unit/retained.c b/test/unit/retained.c
index 76bda50..53c90f2 100644
--- a/test/unit/retained.c
+++ b/test/unit/retained.c
@@ -104,7 +104,7 @@ TEST_BEGIN(test_retained) {
 
 	arena_ind = do_arena_create(NULL);
 	sz = nallocx(HUGEPAGE, 0);
-	size_t guard_sz = san_enabled() ? PAGE_GUARDS_SIZE : 0;
+	size_t guard_sz = san_enabled() ? SAN_PAGE_GUARDS_SIZE : 0;
 	esz = sz + sz_large_pad + guard_sz;
 
 	atomic_store_u(&epoch, 0, ATOMIC_RELAXED);
diff --git a/test/unit/san.c b/test/unit/san.c
index 93e292f..eb9ff51 100644
--- a/test/unit/san.c
+++ b/test/unit/san.c
@@ -122,7 +122,7 @@ TEST_BEGIN(test_guarded_decay) {
 	/* Verify that guarded extents as dirty. */
 	size_t sz1 = PAGE, sz2 = PAGE * 2;
 	/* W/o maps_coalesce, guarded extents are unguarded eagerly. */
-	size_t add_guard_size = maps_coalesce ? 0 : PAGE_GUARDS_SIZE;
+	size_t add_guard_size = maps_coalesce ? 0 : SAN_PAGE_GUARDS_SIZE;
 	generate_dirty(arena_ind, sz1);
 	verify_pdirty(arena_ind, sz1 + add_guard_size);
 	verify_pmuzzy(arena_ind, 0);
diff --git a/test/unit/san_bump.c b/test/unit/san_bump.c
new file mode 100644
index 0000000..fbee53e
--- /dev/null
+++ b/test/unit/san_bump.c
@@ -0,0 +1,111 @@
+#include "test/jemalloc_test.h"
+#include "test/arena_decay.h"
+
+#include "jemalloc/internal/arena_structs.h"
+#include "jemalloc/internal/san_bump.h"
+
+TEST_BEGIN(test_san_bump_alloc) {
+	test_skip_if(!maps_coalesce || !opt_retain);
+
+	tsdn_t *tsdn = tsdn_fetch();
+
+	san_bump_alloc_t sba;
+	san_bump_alloc_init(&sba);
+
+	unsigned arena_ind = do_arena_create(0, 0);
+	assert_u_ne(arena_ind, UINT_MAX, "Failed to create an arena");
+
+	arena_t *arena = arena_get(tsdn, arena_ind, false);
+	pac_t *pac = &arena->pa_shard.pac;
+
+	size_t alloc_size = PAGE * 16;
+	size_t alloc_n = alloc_size / sizeof(unsigned);
+	edata_t* edata = san_bump_alloc(tsdn, &sba, pac, pac_ehooks_get(pac),
+	    alloc_size, /* zero */ false);
+
+	expect_ptr_not_null(edata, "Failed to allocate edata");
+	expect_u_eq(edata_arena_ind_get(edata), arena_ind,
+	    "Edata was assigned an incorrect arena id");
+	expect_zu_eq(edata_size_get(edata), alloc_size,
+	    "Allocated edata of incorrect size");
+	expect_false(edata_slab_get(edata),
+	    "Bump allocator incorrectly assigned 'slab' to true");
+	expect_true(edata_committed_get(edata), "Edata is not committed");
+
+	void *ptr = edata_addr_get(edata);
+	expect_ptr_not_null(ptr, "Edata was assigned an invalid address");
+	/* Test that memory is allocated; no guard pages are misplaced */
+	for (unsigned i = 0; i < alloc_n; ++i) {
+		((unsigned *)ptr)[i] = 1;
+	}
+
+	size_t alloc_size2 = PAGE * 28;
+	size_t alloc_n2 = alloc_size / sizeof(unsigned);
+	edata_t *edata2 = san_bump_alloc(tsdn, &sba, pac, pac_ehooks_get(pac),
+	    alloc_size2, /* zero */ true);
+
+	expect_ptr_not_null(edata2, "Failed to allocate edata");
+	expect_u_eq(edata_arena_ind_get(edata2), arena_ind,
+	    "Edata was assigned an incorrect arena id");
+	expect_zu_eq(edata_size_get(edata2), alloc_size2,
+	    "Allocated edata of incorrect size");
+	expect_false(edata_slab_get(edata2),
+	    "Bump allocator incorrectly assigned 'slab' to true");
+	expect_true(edata_committed_get(edata2), "Edata is not committed");
+
+	void *ptr2 = edata_addr_get(edata2);
+	expect_ptr_not_null(ptr, "Edata was assigned an invalid address");
+
+	uintptr_t ptrdiff = ptr2 > ptr ? (uintptr_t)ptr2 - (uintptr_t)ptr
+	    : (uintptr_t)ptr - (uintptr_t)ptr2;
+	size_t between_allocs = (size_t)ptrdiff - alloc_size;
+
+	expect_zu_ge(between_allocs, PAGE,
+	    "Guard page between allocs is missing");
+
+	for (unsigned i = 0; i < alloc_n2; ++i) {
+		expect_u_eq(((unsigned *)ptr2)[i], 0, "Memory is not zeroed");
+	}
+}
+TEST_END
+
+TEST_BEGIN(test_large_alloc_size) {
+	test_skip_if(!maps_coalesce || !opt_retain);
+
+	tsdn_t *tsdn = tsdn_fetch();
+
+	san_bump_alloc_t sba;
+	san_bump_alloc_init(&sba);
+
+	unsigned arena_ind = do_arena_create(0, 0);
+	assert_u_ne(arena_ind, UINT_MAX, "Failed to create an arena");
+
+	arena_t *arena = arena_get(tsdn, arena_ind, false);
+	pac_t *pac = &arena->pa_shard.pac;
+
+	size_t alloc_size = SBA_RETAINED_ALLOC_SIZE * 2;
+	edata_t* edata = san_bump_alloc(tsdn, &sba, pac, pac_ehooks_get(pac),
+	    alloc_size, /* zero */ false);
+	expect_u_eq(edata_arena_ind_get(edata), arena_ind,
+	    "Edata was assigned an incorrect arena id");
+	expect_zu_eq(edata_size_get(edata), alloc_size,
+	    "Allocated edata of incorrect size");
+	expect_false(edata_slab_get(edata),
+	    "Bump allocator incorrectly assigned 'slab' to true");
+	expect_true(edata_committed_get(edata), "Edata is not committed");
+
+	void *ptr = edata_addr_get(edata);
+	expect_ptr_not_null(ptr, "Edata was assigned an invalid address");
+	/* Test that memory is allocated; no guard pages are misplaced */
+	for (unsigned i = 0; i < alloc_size / PAGE; ++i) {
+		*((char *)ptr + PAGE * i) = 1;
+	}
+}
+TEST_END
+
+int
+main(void) {
+	return test(
+	    test_san_bump_alloc,
+	    test_large_alloc_size);
+}