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[PATCH] Small tcache improvements *
- From: Wilco Dijkstra <Wilco dot Dijkstra at arm dot com>
- To: "libc-alpha at sourceware dot org" <libc-alpha at sourceware dot org>
- Cc: nd <nd at arm dot com>, DJ Delorie <dj at redhat dot com>
- Date: Fri, 10 May 2019 18:03:54 +0000
- Subject: [PATCH] Small tcache improvements *
Change the tcache->counts[] entries to uint16_t - this removes
the limit set by char and allows a larger tcache. Since 65535
seems too large, limit MAX_TCACHE_COUNT to 1024.
bench-malloc-thread with 4 threads is ~15% faster on Cortex-A72.
OK for commit?
ChangeLog:
2019-05-10 Wilco Dijkstra <wdijkstr@arm.com>
* malloc/malloc.c (MAX_TCACHE_COUNT): Increase to 1024.
(tcache_put): Remove redundant assert.
(tcache_get): Remove redundant asserts.
(__libc_malloc): Check tcache count is not zero.
* manual/tunables.texi (glibc.malloc.tcache_count): Update maximum.
--
diff --git a/malloc/malloc.c b/malloc/malloc.c
index b8baaa2706d8d274b04b86e27fc72716753530b0..597406854ddbab8706e487a9ff1e1994a2bb2e83 100644
--- a/malloc/malloc.c
+++ b/malloc/malloc.c
@@ -321,6 +321,10 @@ __malloc_assert (const char *assertion, const char *file, unsigned int line,
/* This is another arbitrary limit, which tunables can change. Each
tcache bin will hold at most this number of chunks. */
# define TCACHE_FILL_COUNT 7
+
+/* Maximum chunks in tcache bins for tunables. This value must fit the range
+ of tcache->counts[] entries, else they may overflow. */
+# define MAX_TCACHE_COUNT 1024
#endif
@@ -2901,12 +2905,10 @@ typedef struct tcache_entry
time), this is for performance reasons. */
typedef struct tcache_perthread_struct
{
- char counts[TCACHE_MAX_BINS];
+ uint16_t counts[TCACHE_MAX_BINS];
tcache_entry *entries[TCACHE_MAX_BINS];
} tcache_perthread_struct;
-#define MAX_TCACHE_COUNT 127 /* Maximum value of counts[] entries. */
-
static __thread bool tcache_shutting_down = false;
static __thread tcache_perthread_struct *tcache = NULL;
@@ -2916,7 +2918,6 @@ static __always_inline void
tcache_put (mchunkptr chunk, size_t tc_idx)
{
tcache_entry *e = (tcache_entry *) chunk2mem (chunk);
- assert (tc_idx < TCACHE_MAX_BINS);
/* Mark this chunk as "in the tcache" so the test in _int_free will
detect a double free. */
@@ -2933,8 +2934,6 @@ static __always_inline void *
tcache_get (size_t tc_idx)
{
tcache_entry *e = tcache->entries[tc_idx];
- assert (tc_idx < TCACHE_MAX_BINS);
- assert (tcache->counts[tc_idx] > 0);
tcache->entries[tc_idx] = e->next;
--(tcache->counts[tc_idx]);
e->key = NULL;
@@ -3046,9 +3045,8 @@ __libc_malloc (size_t bytes)
DIAG_PUSH_NEEDS_COMMENT;
if (tc_idx < mp_.tcache_bins
- /*&& tc_idx < TCACHE_MAX_BINS*/ /* to appease gcc */
&& tcache
- && tcache->entries[tc_idx] != NULL)
+ && tcache->counts[tc_idx] > 0)
{
return tcache_get (tc_idx);
}
diff --git a/manual/tunables.texi b/manual/tunables.texi
index ae638823a21b9cc7aca3684c8e3067cb8cd287e0..cc244512d6893f2abddb9f203ab0ff14838b00e2 100644
--- a/manual/tunables.texi
+++ b/manual/tunables.texi
@@ -189,7 +189,7 @@ per-thread cache. The default (and maximum) value is 1032 bytes on
@deftp Tunable glibc.malloc.tcache_count
The maximum number of chunks of each size to cache. The default is 7.
-The upper limit is 127. If set to zero, the per-thread cache is effectively
+The upper limit is 1024. If set to zero, the per-thread cache is effectively
disabled.
The approximate maximum overhead of the per-thread cache is thus equal