From 26d23da6cd91e4d7d6210c89de5194dedf0f0f60 Mon Sep 17 00:00:00 2001
From: Jason Evans <jasone@canonware.com>
Date: Thu, 9 Mar 2017 17:20:00 -0800
Subject: [PATCH] Prefer pages_purge_forced() over memset().

This has the dual advantages of allowing for sparsely used large
allocations, and relying on the kernel to supply zeroed pages, which
tends to be very fast on modern systems.
---
 src/extent.c | 13 ++++++++++---
 src/large.c  | 33 ++++++++++++++++++++-------------
 2 files changed, 30 insertions(+), 16 deletions(-)

diff --git a/src/extent.c b/src/extent.c
index 33589394..c44ecb89 100644
--- a/src/extent.c
+++ b/src/extent.c
@@ -759,8 +759,11 @@ extent_recycle(tsdn_t *tsdn, arena_t *arena, extent_hooks_t **r_extent_hooks,
 
 	if (*zero) {
 		if (!extent_zeroed_get(extent)) {
-			memset(extent_addr_get(extent), 0,
-			    extent_usize_get(extent));
+			if (pages_purge_forced(extent_base_get(extent),
+			    extent_size_get(extent))) {
+				memset(extent_addr_get(extent), 0,
+				    extent_usize_get(extent));
+			}
 		} else if (config_debug) {
 			size_t i;
 			size_t *p = (size_t *)(uintptr_t)
@@ -971,7 +974,11 @@ extent_grow_retained(tsdn_t *tsdn, arena_t *arena,
 		extent_interior_register(tsdn, rtree_ctx, extent);
 	}
 	if (*zero && !extent_zeroed_get(extent)) {
-		memset(extent_addr_get(extent), 0, extent_usize_get(extent));
+		if (pages_purge_forced(extent_base_get(extent),
+		    extent_size_get(extent))) {
+			memset(extent_addr_get(extent), 0,
+			    extent_usize_get(extent));
+		}
 	}
 	/*
 	 * Increment extent_grow_next, but take care to do so atomically and
diff --git a/src/large.c b/src/large.c
index e9536bca..5145f418 100644
--- a/src/large.c
+++ b/src/large.c
@@ -25,9 +25,13 @@ large_palloc(tsdn_t *tsdn, arena_t *arena, size_t usize, size_t alignment,
 		return NULL;
 	}
 
+	if (config_fill && unlikely(opt_zero)) {
+		zero = true;
+	}
 	/*
-	 * Copy zero into is_zeroed and pass the copy to extent_alloc(), so that
-	 * it is possible to make correct junk/zero fill decisions below.
+	 * Copy zero into is_zeroed and pass the copy when allocating the
+	 * extent, so that it is possible to make correct junk/zero fill
+	 * decisions below, even if is_zeroed ends up true when zero is false.
 	 */
 	is_zeroed = zero;
 	if (likely(!tsdn_null(tsdn))) {
@@ -46,11 +50,8 @@ large_palloc(tsdn_t *tsdn, arena_t *arena, size_t usize, size_t alignment,
 		prof_idump(tsdn);
 	}
 
-	if (zero || (config_fill && unlikely(opt_zero))) {
-		if (!is_zeroed) {
-			memset(extent_addr_get(extent), 0,
-			    extent_usize_get(extent));
-		}
+	if (zero) {
+		assert(is_zeroed);
 	} else if (config_fill && unlikely(opt_junk_alloc)) {
 		memset(extent_addr_get(extent), JEMALLOC_ALLOC_JUNK,
 		    extent_usize_get(extent));
@@ -144,7 +145,16 @@ large_ralloc_no_move_expand(tsdn_t *tsdn, extent_t *extent, size_t usize,
 		return true;
 	}
 
-	bool is_zeroed_trail = false;
+	if (config_fill && unlikely(opt_zero)) {
+		zero = true;
+	}
+	/*
+	 * Copy zero into is_zeroed_trail and pass the copy when allocating the
+	 * extent, so that it is possible to make correct junk/zero fill
+	 * decisions below, even if is_zeroed_trail ends up true when zero is
+	 * false.
+	 */
+	bool is_zeroed_trail = zero;
 	bool commit = true;
 	extent_t *trail;
 	bool new_mapping;
@@ -174,7 +184,7 @@ large_ralloc_no_move_expand(tsdn_t *tsdn, extent_t *extent, size_t usize,
 		arena_stats_mapped_add(tsdn, &arena->stats, trailsize);
 	}
 
-	if (zero || (config_fill && unlikely(opt_zero))) {
+	if (zero) {
 		if (config_cache_oblivious) {
 			/*
 			 * Zero the trailing bytes of the original allocation's
@@ -191,10 +201,7 @@ large_ralloc_no_move_expand(tsdn_t *tsdn, extent_t *extent, size_t usize,
 			assert(nzero > 0);
 			memset(zbase, 0, nzero);
 		}
-		if (!is_zeroed_trail) {
-			memset((void *)((uintptr_t)extent_addr_get(extent) +
-			    oldusize), 0, usize - oldusize);
-		}
+		assert(is_zeroed_trail);
 	} else if (config_fill && unlikely(opt_junk_alloc)) {
 		memset((void *)((uintptr_t)extent_addr_get(extent) + oldusize),
 		    JEMALLOC_ALLOC_JUNK, usize - oldusize);