Add --with-lg-tiny-min, generalize --with-lg-quantum.
diff --git a/INSTALL b/INSTALL
index 73bf718..a00960a 100644
--- a/INSTALL
+++ b/INSTALL
@@ -230,10 +230,9 @@
roughly <lg-size-class-group>=4, depending on page size.
--with-lg-quantum=<lg-quantum>
- Specify the base 2 log of the minimum allocation alignment (only
- <lg-quantum>=3 and <lg-quantum>=4 are supported). jemalloc needs to know
- the minimum alignment that meets the following C standard requirement
- (quoted from the April 12, 2011 draft of the C11 standard):
+ Specify the base 2 log of the minimum allocation alignment. jemalloc needs
+ to know the minimum alignment that meets the following C standard
+ requirement (quoted from the April 12, 2011 draft of the C11 standard):
The pointer returned if the allocation succeeds is suitably aligned so
that it may be assigned to a pointer to any type of object with a
@@ -247,8 +246,8 @@
(<lg-quantum>=4), but the glibc developers chose not to meet this requirement
for performance reasons. An old discussion can be found at
https://sourceware.org/bugzilla/show_bug.cgi?id=206 . Unlike glibc,
- jemalloc does follow the C standard by default (caveat: jemalloc technically
- cheats by only providing 8-byte alignment for 8-byte allocation requests),
+ jemalloc does follow the C standard by default (caveat: jemalloc
+ technically cheats if --with-lg-tiny-min is smaller than --with-lg-quantum),
but the fact that Linux systems already work around this allocator
noncompliance means that it is generally safe in practice to let jemalloc's
minimum alignment follow glibc's lead. If you specify --with-lg-quantum=3
@@ -256,6 +255,27 @@
are not 16-byte-aligned (24, 40, and 56, assuming
--with-lg-size-class-group=2).
+--with-lg-tiny-min=<lg-tiny-min>
+ Specify the base 2 log of the minimum tiny size class to support. Tiny
+ size classes are powers of 2 less than the quantum, and are only
+ incorporated if <lg-tiny-min> is less than <lg-quantum> (see
+ --with-lg-quantum). Tiny size classes technically violate the C standard
+ requirement for minimum alignment, and crashes could conceivably result if
+ the compiler were to generate instructions that made alignment assumptions,
+ both because illegal instruction traps could result, and because accesses
+ could straddle page boundaries and cause segmentation faults due to
+ accessing unmapped addresses.
+
+ The default of <lg-tiny-min>=3 works well in practice even on architectures
+ that technically require 16-byte alignment, probably for the same reason
+ --with-lg-quantum=3 works. Smaller tiny size classes can, and will, cause
+ crashes (see https://bugzilla.mozilla.org/show_bug.cgi?id=691003 for an
+ example).
+
+ This option is rarely useful, and is mainly provided as documentation of a
+ subtle implementation detail. If you do use this option, specify a
+ value in [3, ..., <lg-quantum>].
+
The following environment variables (not a definitive list) impact configure's
behavior:
diff --git a/configure.ac b/configure.ac
index cc30da9..a7bf103 100644
--- a/configure.ac
+++ b/configure.ac
@@ -207,7 +207,7 @@
CPU_SPINWAIT=""
case "${host_cpu}" in
i686|x86_64)
- AC_CACHE_CHECK([whether pause instruction is compilable], [je_cv_pause],
+ AC_CACHE_VAL([je_cv_pause],
[JE_COMPILABLE([pause instruction], [],
[[__asm__ volatile("pause"); return 0;]],
[je_cv_pause])])
@@ -970,10 +970,21 @@
fi
fi
+AC_ARG_WITH([lg_tiny_min],
+ [AS_HELP_STRING([--with-lg-tiny-min=<lg-tiny-min>],
+ [Base 2 log of minimum tiny size class to support])],
+ [LG_TINY_MIN="$with_lg_tiny_min"],
+ [LG_TINY_MIN="3"])
+AC_DEFINE_UNQUOTED([LG_TINY_MIN], [$LG_TINY_MIN])
+
AC_ARG_WITH([lg_quantum],
[AS_HELP_STRING([--with-lg-quantum=<lg-quantum>],
[Base 2 log of minimum allocation alignment])],
- [AC_DEFINE_UNQUOTED([LG_QUANTUM], [$with_lg_quantum])])
+ [LG_QUANTA="$with_lg_quantum"],
+ [LG_QUANTA="3 4"])
+if test "x$with_lg_quantum" != "x" ; then
+ AC_DEFINE_UNQUOTED([LG_QUANTUM], [$with_lg_quantum])
+fi
AC_ARG_WITH([lg_page],
[AS_HELP_STRING([--with-lg-page=<lg-page>], [Base 2 log of system page size])],
@@ -1480,11 +1491,13 @@
])
AC_CONFIG_COMMANDS([include/jemalloc/internal/size_classes.h], [
mkdir -p "${objroot}include/jemalloc/internal"
- "${srcdir}/include/jemalloc/internal/size_classes.sh" ${LG_PAGE_SIZES} ${LG_SIZE_CLASS_GROUP} > "${objroot}include/jemalloc/internal/size_classes.h"
+ "${srcdir}/include/jemalloc/internal/size_classes.sh" "${LG_QUANTA}" ${LG_TINY_MIN} "${LG_PAGE_SIZES}" ${LG_SIZE_CLASS_GROUP} > "${objroot}include/jemalloc/internal/size_classes.h"
], [
srcdir="${srcdir}"
objroot="${objroot}"
- LG_PAGE_SIZES=${LG_PAGE_SIZES}
+ LG_QUANTA="${LG_QUANTA}"
+ LG_TINY_MIN=${LG_TINY_MIN}
+ LG_PAGE_SIZES="${LG_PAGE_SIZES}"
LG_SIZE_CLASS_GROUP=${LG_SIZE_CLASS_GROUP}
])
AC_CONFIG_COMMANDS([include/jemalloc/jemalloc_protos_jet.h], [
diff --git a/include/jemalloc/internal/jemalloc_internal.h.in b/include/jemalloc/internal/jemalloc_internal.h.in
index 3f65fad..294e2cc 100644
--- a/include/jemalloc/internal/jemalloc_internal.h.in
+++ b/include/jemalloc/internal/jemalloc_internal.h.in
@@ -181,7 +181,6 @@
(((unsigned)(flags >> 8)) - 1)
/* Smallest size class to support. */
-#define LG_TINY_MIN 3
#define TINY_MIN (1U << LG_TINY_MIN)
/*
diff --git a/include/jemalloc/internal/jemalloc_internal_defs.h.in b/include/jemalloc/internal/jemalloc_internal_defs.h.in
index 0ff939c..dccbb1e 100644
--- a/include/jemalloc/internal/jemalloc_internal_defs.h.in
+++ b/include/jemalloc/internal/jemalloc_internal_defs.h.in
@@ -144,6 +144,9 @@
/* Support lazy locking (avoid locking unless a second thread is launched). */
#undef JEMALLOC_LAZY_LOCK
+/* Minimum size class to support is 2^LG_TINY_MIN bytes. */
+#undef LG_TINY_MIN
+
/*
* Minimum allocation alignment is 2^LG_QUANTUM bytes (ignoring tiny size
* classes).
diff --git a/include/jemalloc/internal/size_classes.sh b/include/jemalloc/internal/size_classes.sh
index 733338c..38020dc 100755
--- a/include/jemalloc/internal/size_classes.sh
+++ b/include/jemalloc/internal/size_classes.sh
@@ -1,6 +1,6 @@
#!/bin/sh
#
-# Usage: size_classes.sh <lg_parr> <lg_g>
+# Usage: size_classes.sh <lg_qarr> <lg_tmin> <lg_parr> <lg_g>
# The following limits are chosen such that they cover all supported platforms.
@@ -8,19 +8,19 @@
lg_zarr="2 3"
# Quanta.
-lg_qarr="3 4"
+lg_qarr=$1
# The range of tiny size classes is [2^lg_tmin..2^(lg_q-1)].
-lg_tmin=3
+lg_tmin=$2
# Maximum lookup size.
lg_kmax=12
# Page sizes.
-lg_parr=`echo $1 | tr ',' ' '`
+lg_parr=`echo $3 | tr ',' ' '`
# Size class group size (number of size classes for each size doubling).
-lg_g=$2
+lg_g=$4
pow2() {
e=$1
diff --git a/src/jemalloc.c b/src/jemalloc.c
index fc490eb..4543959 100644
--- a/src/jemalloc.c
+++ b/src/jemalloc.c
@@ -60,15 +60,69 @@
JEMALLOC_ALIGNED(CACHELINE)
const uint8_t size2index_tab[] = {
+#if LG_TINY_MIN == 0
+#warning "Dangerous LG_TINY_MIN"
+#define S2B_0(i) i,
+#elif LG_TINY_MIN == 1
+#warning "Dangerous LG_TINY_MIN"
+#define S2B_1(i) i,
+#elif LG_TINY_MIN == 2
+#warning "Dangerous LG_TINY_MIN"
+#define S2B_2(i) i,
+#elif LG_TINY_MIN == 3
#define S2B_3(i) i,
+#elif LG_TINY_MIN == 4
+#define S2B_4(i) i,
+#elif LG_TINY_MIN == 5
+#define S2B_5(i) i,
+#elif LG_TINY_MIN == 6
+#define S2B_6(i) i,
+#elif LG_TINY_MIN == 7
+#define S2B_7(i) i,
+#elif LG_TINY_MIN == 8
+#define S2B_8(i) i,
+#elif LG_TINY_MIN == 9
+#define S2B_9(i) i,
+#elif LG_TINY_MIN == 10
+#define S2B_10(i) i,
+#elif LG_TINY_MIN == 11
+#define S2B_11(i) i,
+#else
+#error "Unsupported LG_TINY_MIN"
+#endif
+#if LG_TINY_MIN < 1
+#define S2B_1(i) S2B_0(i) S2B_0(i)
+#endif
+#if LG_TINY_MIN < 2
+#define S2B_2(i) S2B_1(i) S2B_1(i)
+#endif
+#if LG_TINY_MIN < 3
+#define S2B_3(i) S2B_2(i) S2B_2(i)
+#endif
+#if LG_TINY_MIN < 4
#define S2B_4(i) S2B_3(i) S2B_3(i)
+#endif
+#if LG_TINY_MIN < 5
#define S2B_5(i) S2B_4(i) S2B_4(i)
+#endif
+#if LG_TINY_MIN < 6
#define S2B_6(i) S2B_5(i) S2B_5(i)
+#endif
+#if LG_TINY_MIN < 7
#define S2B_7(i) S2B_6(i) S2B_6(i)
+#endif
+#if LG_TINY_MIN < 8
#define S2B_8(i) S2B_7(i) S2B_7(i)
+#endif
+#if LG_TINY_MIN < 9
#define S2B_9(i) S2B_8(i) S2B_8(i)
+#endif
+#if LG_TINY_MIN < 10
#define S2B_10(i) S2B_9(i) S2B_9(i)
+#endif
+#if LG_TINY_MIN < 11
#define S2B_11(i) S2B_10(i) S2B_10(i)
+#endif
#define S2B_no(i)
#define SC(index, lg_grp, lg_delta, ndelta, bin, lg_delta_lookup) \
S2B_##lg_delta_lookup(index)