Add clipping support to lg_chunk option processing.

Modify processing of the lg_chunk option so that it clips an
out-of-range input to the edge of the valid range.  This makes it
possible to request the minimum possible chunk size without intimate
knowledge of allocator internals.

Submitted by Ian Lepore (see FreeBSD PR bin/174641).

doc/jemalloc.xml.in

@@ -790,8 +790,11 @@ for (i = 0; i < nbins; i++) {
           (<type>size_t</type>)
           <literal>r-</literal>
         </term>
-        <listitem><para>Virtual memory chunk size (log base 2).  The default
+        <listitem><para>Virtual memory chunk size (log base 2).  If a chunk
-        chunk size is 4 MiB (2^22).</para></listitem>
+        size outside the supported size range is specified, the size is
+        silently clipped to the minimum/maximum supported size.  The default
+        chunk size is 4 MiB (2^22).
+        </para></listitem>
       </varlistentry>
 
       <varlistentry id="opt.dss">

src/jemalloc.c

@@ -469,7 +469,7 @@ malloc_conf_init(void)
 
 		while (*opts != '\0' && malloc_conf_next(&opts, &k, &klen, &v,
 		    &vlen) == false) {
-#define	CONF_HANDLE_BOOL_HIT(o, n, hit)					\
+#define	CONF_HANDLE_BOOL(o, n)						\
 			if (sizeof(n)-1 == klen && strncmp(n, k,	\
 			    klen) == 0) {				\
 				if (strncmp("true", v, vlen) == 0 &&	\
@@ -483,16 +483,9 @@ malloc_conf_init(void)
 					    "Invalid conf value",	\
 					    k, klen, v, vlen);		\
 				}					\
-				hit = true;				\
-			} else						\
-				hit = false;
-#define	CONF_HANDLE_BOOL(o, n) {					\
-			bool hit;					\
-			CONF_HANDLE_BOOL_HIT(o, n, hit);		\
-			if (hit)					\
 				continue;				\
-}
+			}
-#define	CONF_HANDLE_SIZE_T(o, n, min, max)				\
+#define	CONF_HANDLE_SIZE_T(o, n, min, max, clip)			\
 			if (sizeof(n)-1 == klen && strncmp(n, k,	\
 			    klen) == 0) {				\
 				uintmax_t um;				\
@@ -505,12 +498,22 @@ malloc_conf_init(void)
 					malloc_conf_error(		\
 					    "Invalid conf value",	\
 					    k, klen, v, vlen);		\
-				} else if (um < min || um > max) {	\
+				} else if (clip) {			\
-					malloc_conf_error(		\
+					if (um < min)			\
-					    "Out-of-range conf value",	\
+						o = min;		\
-					    k, klen, v, vlen);		\
+					else if (um > max)		\
-				} else					\
+						o = max;		\
-					o = um;				\
+					else				\
+						o = um;			\
+				} else {				\
+					if (um < min || um > max) {	\
+						malloc_conf_error(	\
+						    "Out-of-range "	\
+						    "conf value",	\
+						    k, klen, v, vlen);	\
+					} else				\
+						o = um;			\
+				}					\
 				continue;				\
 			}
 #define	CONF_HANDLE_SSIZE_T(o, n, min, max)				\
@@ -555,7 +558,8 @@ malloc_conf_init(void)
 			 * config_fill.
 			 */
 			CONF_HANDLE_SIZE_T(opt_lg_chunk, "lg_chunk", LG_PAGE +
-			    (config_fill ? 2 : 1), (sizeof(size_t) << 3) - 1)
+			    (config_fill ? 2 : 1), (sizeof(size_t) << 3) - 1,
+			    true)
 			if (strncmp("dss", k, klen) == 0) {
 				int i;
 				bool match = false;
@@ -581,14 +585,14 @@ malloc_conf_init(void)
 				continue;
 			}
 			CONF_HANDLE_SIZE_T(opt_narenas, "narenas", 1,
-			    SIZE_T_MAX)
+			    SIZE_T_MAX, false)
 			CONF_HANDLE_SSIZE_T(opt_lg_dirty_mult, "lg_dirty_mult",
 			    -1, (sizeof(size_t) << 3) - 1)
 			CONF_HANDLE_BOOL(opt_stats_print, "stats_print")
 			if (config_fill) {
 				CONF_HANDLE_BOOL(opt_junk, "junk")
 				CONF_HANDLE_SIZE_T(opt_quarantine, "quarantine",
-				    0, SIZE_T_MAX)
+				    0, SIZE_T_MAX, false)
 				CONF_HANDLE_BOOL(opt_redzone, "redzone")
 				CONF_HANDLE_BOOL(opt_zero, "zero")
 			}