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Re: [patchv3] malloc: add mxfast tunable
- From: Carlos O'Donell <carlos at redhat dot com>
- To: DJ Delorie <dj at redhat dot com>
- Cc: libc-alpha at sourceware dot org
- Date: Fri, 9 Aug 2019 12:23:12 -0400
- Subject: Re: [patchv3] malloc: add mxfast tunable
- References: <xnblwzp7vf.fsf@greed.delorie.com>
On 8/8/19 7:14 PM, DJ Delorie wrote:
"Carlos O'Donell" <carlos@redhat.com> writes:
Reviewed. Please post v3. Three changes requested:
* Set mxfast to 0 in env var.
* Paragraph about intent of test.
* Clarify language in manual.
Done.
+tst-mxfast-ENV = GLIBC_TUNABLES=glibc.malloc.tcache_count=0:glibc.malloc.mxfast=1
Why isn't this 0?
I don't recall exactly, but at the time the value zero was a special
case for "default" or something, so a value of 1 bypasses that. I ran
the test case with =0 and =1, and both passed (and =160 failed) so I
changed it to =0.
This looks good to me now. OK for master.
Reviewed-by: Carlos O'Donell <carlos@redhat.com>
From 19869bd9dd8c20b3c96256a90588c6dce0f582af Mon Sep 17 00:00:00 2001
From: DJ Delorie <dj@delorie.com>
Date: Thu, 8 Aug 2019 19:09:43 -0400
Subject: Add glibc.malloc.mxfast tunable
* elf/dl-tunables.list: Add glibc.malloc.mxfast.
* manual/tunables.texi: Document it.
* malloc/malloc.c (do_set_mxfast): New.
(__libc_mallopt): Call it.
* malloc/arena.c: Add mxfast tunable.
* malloc/tst-mxfast.c: New.
* malloc/Makefile: Add it.
diff --git a/ChangeLog b/ChangeLog
index 760698b440..6f9bc2fe3e 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,13 @@
+2019-08-08 DJ Delorie <dj@redhat.com>
+
+ * elf/dl-tunables.list: Add glibc.malloc.mxfast.
+ * manual/tunables.texi: Document it.
+ * malloc/malloc.c (do_set_mxfast): New.
+ (__libc_mallopt): Call it.
+ * malloc/arena.c: Add mxfast tunable.
+ * malloc/tst-mxfast.c: New.
+ * malloc/Makefile: Add it.
OK.
+
2019-08-07 Joseph Myers <joseph@codesourcery.com>
* sysdeps/unix/sysv/linux/bits/fcntl-linux.h [__USE_GNU]
diff --git a/elf/dl-tunables.list b/elf/dl-tunables.list
index 1fc2d8886b..525c3767b5 100644
--- a/elf/dl-tunables.list
+++ b/elf/dl-tunables.list
@@ -85,6 +85,11 @@ glibc {
tcache_unsorted_limit {
type: SIZE_T
}
+ mxfast {
+ type: SIZE_T
+ minval: 0
+ security_level: SXID_IGNORE
OK.
+ }
}
cpu {
hwcap_mask {
diff --git a/malloc/Makefile b/malloc/Makefile
index d2fba29953..94b74b5c45 100644
--- a/malloc/Makefile
+++ b/malloc/Makefile
@@ -39,6 +39,7 @@ tests := mallocbug tst-malloc tst-valloc tst-calloc tst-obstack \
tst-malloc-too-large \
tst-malloc-stats-cancellation \
tst-tcfree1 tst-tcfree2 tst-tcfree3 \
+ tst-mxfast \
OK.
tests-static := \
tst-interpose-static-nothread \
@@ -196,6 +197,8 @@ tst-malloc-usable-static-ENV = $(tst-malloc-usable-ENV)
tst-malloc-usable-tunables-ENV = GLIBC_TUNABLES=glibc.malloc.check=3
tst-malloc-usable-static-tunables-ENV = $(tst-malloc-usable-tunables-ENV)
+tst-mxfast-ENV = GLIBC_TUNABLES=glibc.malloc.tcache_count=0:glibc.malloc.mxfast=0
OK.
+
ifeq ($(experimental-malloc),yes)
CPPFLAGS-malloc.c += -DUSE_TCACHE=1
else
diff --git a/malloc/arena.c b/malloc/arena.c
index 8309c1334c..a32eb403ec 100644
--- a/malloc/arena.c
+++ b/malloc/arena.c
@@ -236,6 +236,7 @@ TUNABLE_CALLBACK_FNDECL (set_tcache_max, size_t)
TUNABLE_CALLBACK_FNDECL (set_tcache_count, size_t)
TUNABLE_CALLBACK_FNDECL (set_tcache_unsorted_limit, size_t)
#endif
+TUNABLE_CALLBACK_FNDECL (set_mxfast, size_t)
OK.
#else
/* Initialization routine. */
#include <string.h>
@@ -323,6 +324,7 @@ ptmalloc_init (void)
TUNABLE_GET (tcache_unsorted_limit, size_t,
TUNABLE_CALLBACK (set_tcache_unsorted_limit));
# endif
+ TUNABLE_GET (mxfast, size_t, TUNABLE_CALLBACK (set_mxfast));
OK.
#else
const char *s = NULL;
if (__glibc_likely (_environ != NULL))
diff --git a/malloc/malloc.c b/malloc/malloc.c
index 343d89f489..2e4d8f246c 100644
--- a/malloc/malloc.c
+++ b/malloc/malloc.c
@@ -5115,6 +5115,19 @@ do_set_tcache_unsorted_limit (size_t value)
}
#endif
+static inline int
+__always_inline
+do_set_mxfast (size_t value)
+{
+ if (value >= 0 && value <= MAX_FAST_SIZE)
+ {
+ LIBC_PROBE (memory_mallopt_mxfast, 2, value, get_max_fast ());
+ set_max_fast (value);
+ return 1;
+ }
+ return 0;
OK.
+}
+
int
__libc_mallopt (int param_number, int value)
{
@@ -5134,13 +5147,7 @@ __libc_mallopt (int param_number, int value)
switch (param_number)
{
case M_MXFAST:
- if (value >= 0 && value <= MAX_FAST_SIZE)
- {
- LIBC_PROBE (memory_mallopt_mxfast, 2, value, get_max_fast ());
- set_max_fast (value);
- }
- else
- res = 0;
+ do_set_mxfast (value);
OK.
break;
case M_TRIM_THRESHOLD:
diff --git a/malloc/tst-mxfast.c b/malloc/tst-mxfast.c
new file mode 100644
index 0000000000..7a371d2f9d
--- /dev/null
+++ b/malloc/tst-mxfast.c
@@ -0,0 +1,50 @@
+/* Test that glibc.malloc.mxfast tunable works.
+ Copyright (C) 2018, 2019 Free Software Foundation, Inc.
+ This file is part of the GNU C Library.
+
+ The GNU C Library is free software; you can redistribute it and/or
+ modify it under the terms of the GNU Lesser General Public
+ License as published by the Free Software Foundation; either
+ version 2.1 of the License, or (at your option) any later version.
+
+ The GNU C Library is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public
+ License along with the GNU C Library; if not, see
+ <http://www.gnu.org/licenses/>. */
+
+/* This test verifies that setting the glibc.malloc.mxfast tunable to
+ zero results in free'd blocks being returned to the small bins, not
+ the fast bins. */
OK.
+
+#include <malloc.h>
+#include <assert.h>
+
+int
+do_test(void)
+{
+ struct mallinfo m;
+ char * volatile p1;
+ char * volatile p2;
+
+ /* Arbitrary value; must be in default fastbin range. */
+ p1 = malloc (3);
+ /* Something large so that p1 isn't a "top block" */
+ p2 = malloc (512);
+ free (p1);
+
+ m = mallinfo();
+
+ /* This will fail if there are any blocks in the fastbins. */
+ assert (m.smblks == 0);
OK. Perfect.
+
+ /* To keep gcc happy. */
+ free (p2);
+
+ return 0;
+}
+
+#include <support/test-driver.c>
diff --git a/manual/tunables.texi b/manual/tunables.texi
index ee0fdf28d1..1687f9c939 100644
--- a/manual/tunables.texi
+++ b/manual/tunables.texi
@@ -214,6 +214,18 @@ pre-fill the per-thread cache with. The default, or when set to zero,
is no limit.
@end deftp
+@deftp Tunable glibc.malloc.mxfast
+One of the optimizations malloc uses is to maintain a series of ``fast
+bins'' that hold chunks up to a specific size. The default and
+maximum size which may be held this way is 80 bytes on 32-bit systems
+or 160 bytes on 64-bit systems. Applications which value size over
+speed may choose to reduce the size of requests which are serviced
+from fast bins with this tunable. Note that the value specified
+includes malloc's internal overhead, which is normally the size of one
+pointer, so add 4 on 32-bit systems or 8 on 64-bit systems to the size
+passed to @code{malloc} for the largest bin size to enable.
+@end deftp
OK.
+
@node Elision Tunables
@section Elision Tunables
@cindex elision tunables
--
Cheers,
Carlos.