buffer: do not round up allocation for reference-type chain objects

Skip rounding up memory allocations for:
  * evbuffer_add_reference()
  * evbuffer_add_buffer_reference()
  * evbuffer_add_file_segment()

These chain objects only store small structs with references to
other things, and these small structs do not themselves grow, so
bumping up the allocation to MIN_BUFFER_SIZE (512 bytes) is wasteful.

1 files changed, 37 insertions, 27 deletions

diff --git a/buffer.c b/buffer.c
index 822d97a5..6c96f054 100644
--- a/buffer.c
+++ b/buffer.c
@@ -158,17 +158,7 @@ evbuffer_chain_new(size_t size)
 	if (size > EVBUFFER_CHAIN_MAX - EVBUFFER_CHAIN_SIZE)
 		return (NULL);
 
-	size += EVBUFFER_CHAIN_SIZE;
-
-	/* get the next largest memory that can hold the buffer */
-	if (size < EVBUFFER_CHAIN_MAX / 2) {
-		to_alloc = MIN_BUFFER_SIZE;
-		while (to_alloc < size) {
-			to_alloc <<= 1;
-		}
-	} else {
-		to_alloc = size;
-	}
+	to_alloc = size + EVBUFFER_CHAIN_SIZE;
 
 	/* we get everything in one chunk */
 	if ((chain = mm_malloc(to_alloc)) == NULL)
@@ -188,6 +178,29 @@ evbuffer_chain_new(size_t size)
 	return (chain);
 }
 
+static struct evbuffer_chain *
+evbuffer_chain_new_membuf(size_t size)
+{
+	size_t to_alloc;
+
+	if (size > EVBUFFER_CHAIN_MAX - EVBUFFER_CHAIN_SIZE)
+		return (NULL);
+
+	size += EVBUFFER_CHAIN_SIZE;
+
+	/* get the next largest memory that can hold the buffer */
+	if (size < EVBUFFER_CHAIN_MAX / 2) {
+		to_alloc = MIN_BUFFER_SIZE;
+		while (to_alloc < size) {
+			to_alloc <<= 1;
+		}
+	} else {
+		to_alloc = size;
+	}
+
+	return evbuffer_chain_new(to_alloc - EVBUFFER_CHAIN_SIZE);
+}
+
 static inline void
 evbuffer_chain_free(struct evbuffer_chain *chain)
 {
@@ -326,7 +339,7 @@ static inline struct evbuffer_chain *
 evbuffer_chain_insert_new(struct evbuffer *buf, size_t datlen)
 {
 	struct evbuffer_chain *chain;
-	if ((chain = evbuffer_chain_new(datlen)) == NULL)
+	if ((chain = evbuffer_chain_new_membuf(datlen)) == NULL)
 		return NULL;
 	evbuffer_chain_insert(buf, chain);
 	return chain;
@@ -849,7 +862,7 @@ PRESERVE_PINNED(struct evbuffer *src, struct evbuffer_chain **first,
 		struct evbuffer_chain *tmp;
 
 		EVUTIL_ASSERT(pinned == src->last_with_datap);
-		tmp = evbuffer_chain_new(chain->off);
+		tmp = evbuffer_chain_new_membuf(chain->off);
 		if (!tmp)
 			return -1;
 		memcpy(tmp->buffer, chain->buffer + chain->misalign,
@@ -1418,7 +1431,7 @@ evbuffer_pullup(struct evbuffer *buf, ev_ssize_t size)
 		size -= old_off;
 		chain = chain->next;
 	} else {
-		if ((tmp = evbuffer_chain_new(size)) == NULL) {
+		if ((tmp = evbuffer_chain_new_membuf(size)) == NULL) {
 			event_warn("%s: out of memory", __func__);
 			goto done;
 		}
@@ -1766,10 +1779,9 @@ evbuffer_add(struct evbuffer *buf, const void *data_in, size_t datlen)
 	/* If there are no chains allocated for this buffer, allocate one
 	 * big enough to hold all the data. */
 	if (chain == NULL) {
-		chain = evbuffer_chain_new(datlen);
+		chain = evbuffer_chain_insert_new(buf, datlen);
 		if (!chain)
 			goto done;
-		evbuffer_chain_insert(buf, chain);
 	}
 
 	if ((chain->flags & EVBUFFER_IMMUTABLE) == 0) {
@@ -1808,7 +1820,7 @@ evbuffer_add(struct evbuffer *buf, const void *data_in, size_t datlen)
 		to_alloc <<= 1;
 	if (datlen > to_alloc)
 		to_alloc = datlen;
-	tmp = evbuffer_chain_new(to_alloc);
+	tmp = evbuffer_chain_new_membuf(to_alloc);
 	if (tmp == NULL)
 		goto done;
 
@@ -1858,10 +1870,9 @@ evbuffer_prepend(struct evbuffer *buf, const void *data, size_t datlen)
 	chain = buf->first;
 
 	if (chain == NULL) {
-		chain = evbuffer_chain_new(datlen);
+		chain = evbuffer_chain_insert_new(buf, datlen);
 		if (!chain)
 			goto done;
-		evbuffer_chain_insert(buf, chain);
 	}
 
 	/* we cannot touch immutable buffers */
@@ -1898,7 +1909,7 @@ evbuffer_prepend(struct evbuffer *buf, const void *data, size_t datlen)
 	}
 
 	/* we need to add another chain */
-	if ((tmp = evbuffer_chain_new(datlen)) == NULL)
+	if ((tmp = evbuffer_chain_new_membuf(datlen)) == NULL)
 		goto done;
 	buf->first = tmp;
 	if (buf->last_with_datap == &buf->first && chain->off)
@@ -2027,7 +2038,7 @@ evbuffer_expand_singlechain(struct evbuffer *buf, size_t datlen)
 		 * MAX_TO_COPY_IN_EXPAND bytes. */
 		/* figure out how much space we need */
 		size_t length = chain->off + datlen;
-		struct evbuffer_chain *tmp = evbuffer_chain_new(length);
+		struct evbuffer_chain *tmp = evbuffer_chain_new_membuf(length);
 		if (tmp == NULL)
 			goto err;
 
@@ -2073,12 +2084,11 @@ evbuffer_expand_fast_(struct evbuffer *buf, size_t datlen, int n)
 	if (chain == NULL || (chain->flags & EVBUFFER_IMMUTABLE)) {
 		/* There is no last chunk, or we can't touch the last chunk.
 		 * Just add a new chunk. */
-		chain = evbuffer_chain_new(datlen);
+		chain = evbuffer_chain_insert_new(buf, datlen);
 		if (chain == NULL)
 			return (-1);
-
-		evbuffer_chain_insert(buf, chain);
-		return (0);
+		else
+			return (0);
 	}
 
 	used = 0; /* number of chains we're using space in. */
@@ -2116,7 +2126,7 @@ evbuffer_expand_fast_(struct evbuffer *buf, size_t datlen, int n)
 		 * chains; we can add another. */
 		EVUTIL_ASSERT(chain == NULL);
 
-		tmp = evbuffer_chain_new(datlen - avail);
+		tmp = evbuffer_chain_new_membuf(datlen - avail);
 		if (tmp == NULL)
 			return (-1);
 
@@ -2148,7 +2158,7 @@ evbuffer_expand_fast_(struct evbuffer *buf, size_t datlen, int n)
 			evbuffer_chain_free(chain);
 		}
 		EVUTIL_ASSERT(datlen >= avail);
-		tmp = evbuffer_chain_new(datlen - avail);
+		tmp = evbuffer_chain_new_membuf(datlen - avail);
 		if (tmp == NULL) {
 			if (rmv_all) {
 				ZERO_CHAIN(buf);