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Small tcache improvements 

Change the tcache->counts[] entries to uint16_t - this removes
the limit set by char and allows a larger tcache.  Remove a few
redundant asserts.

bench-malloc-thread with 4 threads is ~15% faster on Cortex-A72.

Reviewed-by: DJ Delorie <dj@redhat.com>

	* malloc/malloc.c (MAX_TCACHE_COUNT): Increase to UINT16_MAX.
	(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.

(cherry picked from commit 1f50f2ad854c84ead522bfc7331b46dbe6057d53)
This commit is contained in:
Wilco Dijkstra 2019-05-17 18:16:20 +01:00 committed by Arjun Shankar
parent 9a3ff995bd
commit 0ad788face
3 changed files with 15 additions and 9 deletions
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8
ChangeLog
View File

@ -1,3 +1,11 @@
2019-05-17 Wilco Dijkstra <wdijkstr@arm.com>
* malloc/malloc.c (MAX_TCACHE_COUNT): Increase to UINT16_MAX.
(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.
2019-02-04 Joseph Myers <joseph@codesourcery.com>
* malloc/malloc.c (tcache_get): Compare tcache->counts[tc_idx]

14
malloc/malloc.c
View File

@ -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 UINT16_MAX
#endif
@ -2915,12 +2919,10 @@ 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;
@ -2930,7 +2932,6 @@ 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. */
@ -2947,8 +2948,6 @@ 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;
@ -3053,9 +3052,8 @@ __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);
}

2
manual/tunables.texi
View File

@ -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 65535. If set to zero, the per-thread cache is effectively
disabled.
The approximate maximum overhead of the per-thread cache is thus equal