Use smaller zlib objects when under memory pressure

We add a compression level argument to tor_zlib_new, and use it to
determine how much memory to allocate for the zlib object.  We use the
existing level by default, but shift to smaller levels for small
requests when we have been over 3/4 of our memory usage in the past
half-hour.

Closes ticket 11791.

1 files changed, 39 insertions, 11 deletions

diff --git a/src/common/torgzip.c b/src/common/torgzip.c
index 4480e4b747..05a450e3fb 100644
--- a/src/common/torgzip.c
+++ b/src/common/torgzip.c
@@ -92,10 +92,27 @@ tor_zlib_get_header_version_str(void)
 
 /** Return the 'bits' value to tell zlib to use <b>method</b>.*/
 static INLINE int
-method_bits(compress_method_t method)
+method_bits(compress_method_t method, zlib_compression_level_t level)
 {
   /* Bits+16 means "use gzip" in zlib >= 1.2 */
-  return method == GZIP_METHOD ? 15+16 : 15;
+  const int flag = method == GZIP_METHOD ? 16 : 0;
+  switch (level) {
+    default:
+    case HIGH_COMPRESSION: return flag + 15;
+    case MEDIUM_COMPRESSION: return flag + 13;
+    case LOW_COMPRESSION: return flag + 11;
+  }
+}
+
+static INLINE int
+get_memlevel(zlib_compression_level_t level)
+{
+  switch (level) {
+    default:
+    case HIGH_COMPRESSION: return 8;
+    case MEDIUM_COMPRESSION: return 7;
+    case LOW_COMPRESSION: return 6;
+  }
 }
 
 /** @{ */
@@ -162,8 +179,9 @@ tor_gzip_compress(char **out, size_t *out_len,
   stream->avail_in = (unsigned int)in_len;
 
   if (deflateInit2(stream, Z_BEST_COMPRESSION, Z_DEFLATED,
-                   method_bits(method),
-                   8, Z_DEFAULT_STRATEGY) != Z_OK) {
+                   method_bits(method, HIGH_COMPRESSION),
+                   get_memlevel(HIGH_COMPRESSION),
+                   Z_DEFAULT_STRATEGY) != Z_OK) {
     log_warn(LD_GENERAL, "Error from deflateInit2: %s",
              stream->msg?stream->msg:"<no message>");
     goto err;
@@ -289,7 +307,7 @@ tor_gzip_uncompress(char **out, size_t *out_len,
   stream->avail_in = (unsigned int)in_len;
 
   if (inflateInit2(stream,
-                   method_bits(method)) != Z_OK) {
+                   method_bits(method, HIGH_COMPRESSION)) != Z_OK) {
     log_warn(LD_GENERAL, "Error from inflateInit2: %s",
              stream->msg?stream->msg:"<no message>");
     goto err;
@@ -315,7 +333,8 @@ tor_gzip_uncompress(char **out, size_t *out_len,
           log_warn(LD_BUG, "Error freeing gzip structures");
           goto err;
         }
-        if (inflateInit2(stream, method_bits(method)) != Z_OK) {
+        if (inflateInit2(stream,
+                         method_bits(method,HIGH_COMPRESSION)) != Z_OK) {
           log_warn(LD_GENERAL, "Error from second inflateInit2: %s",
                    stream->msg?stream->msg:"<no message>");
           goto err;
@@ -426,10 +445,11 @@ struct tor_zlib_state_t {
  * <b>compress</b>, it's for compression; otherwise it's for
  * decompression. */
 tor_zlib_state_t *
-tor_zlib_new(int compress, compress_method_t method)
+tor_zlib_new(int compress, compress_method_t method,
+             zlib_compression_level_t compression_level)
 {
   tor_zlib_state_t *out;
-  int bits;
+  int bits, memlevel;
 
   if (method == GZIP_METHOD && !is_gzip_supported()) {
     /* Old zlib version don't support gzip in inflateInit2 */
@@ -437,21 +457,29 @@ tor_zlib_new(int compress, compress_method_t method)
     return NULL;
  }
 
+ if (! compress) {
+   /* use this setting for decompression, since we might have the
+    * max number of window bits */
+   compression_level = HIGH_COMPRESSION;
+ }
+
  out = tor_malloc_zero(sizeof(tor_zlib_state_t));
  out->stream.zalloc = Z_NULL;
  out->stream.zfree = Z_NULL;
  out->stream.opaque = NULL;
  out->compress = compress;
- bits = method_bits(method);
+ bits = method_bits(method, compression_level);
+ memlevel = get_memlevel(compression_level);
  if (compress) {
    if (deflateInit2(&out->stream, Z_BEST_COMPRESSION, Z_DEFLATED,
-                    bits, 8, Z_DEFAULT_STRATEGY) != Z_OK)
+                    bits, memlevel,
+                    Z_DEFAULT_STRATEGY) != Z_OK)
      goto err;
  } else {
    if (inflateInit2(&out->stream, bits) != Z_OK)
      goto err;
  }
- out->allocation = tor_zlib_state_size_precalc(!compress, bits, 8);
+ out->allocation = tor_zlib_state_size_precalc(!compress, bits, memlevel);
 
  total_zlib_allocation += out->allocation;