[core] reduce oversized mem alloc for backends

reduce oversized memory allocations when reading from backends:
avoid extra power-2 allocation for 1 byte ('\0') when data
available to read is exactly power-2

2 files changed, 10 insertions, 6 deletions

diff --git a/src/chunk.c b/src/chunk.c
index 43ee14a1..b88c2636 100644
--- a/src/chunk.c
+++ b/src/chunk.c
@@ -144,7 +144,7 @@ static void chunk_push_oversized(chunk * const c, const size_t sz) {
 }
 
 __attribute_returns_nonnull__
-static buffer * chunk_buffer_acquire_sz(size_t sz) {
+static buffer * chunk_buffer_acquire_sz(const size_t sz) {
     chunk *c;
     buffer *b;
     if (sz <= (chunk_buf_sz|1)) {
@@ -159,11 +159,15 @@ static buffer * chunk_buffer_acquire_sz(size_t sz) {
              * (and if doing so, might replace chunks_oversized_n) */
     }
     else {
-        /*(round up to nearest chunk_buf_sz)*/
-        sz = (sz + (chunk_buf_sz-1)) & ~(chunk_buf_sz-1);
         c = chunk_pop_oversized(sz);
-        if (NULL == c)
-            c = chunk_init(sz);
+        if (NULL == c) {
+            /*(round up to nearest chunk_buf_sz)*/
+            /* NB: round down power-2 + 1 to avoid excess allocation
+             *   (sz & ~1uL) relies on buffer_realloc() adding +1 *and* on callers
+             *   of this func never passing power-2 + 1 sz unless the direct caller
+             *   adds +1 for '\0', as is done in chunk_buffer_prepare_append() */
+            c = chunk_init(((sz & ~1uL)+(chunk_buf_sz-1)) & ~(chunk_buf_sz-1));
+        }
     }
     c->next = chunk_buffers;
     chunk_buffers = c;
diff --git a/src/http-header-glue.c b/src/http-header-glue.c
index 38a3a76d..a70b510c 100644
--- a/src/http-header-glue.c
+++ b/src/http-header-glue.c
@@ -1207,7 +1207,7 @@ handler_t http_response_read(request_st * const r, http_response_opts * const op
 
         if (avail < toread) {
             /*(add avail+toread to reduce allocations when ioctl EOPNOTSUPP)*/
-            avail = avail ? avail - 1 + toread : toread;
+            avail = toread < MAX_READ_LIMIT && avail ? avail-1+toread : toread;
             avail = chunk_buffer_prepare_append(b, avail);
         }