[PATCH v6] malloc: Add tcache path for calloc
H.J. Lu
hjl.tools@gmail.com
Tue Dec 10 21:16:46 GMT 2024
On Wed, Dec 4, 2024 at 7:19 PM Wangyang Guo <wangyang.guo@intel.com> wrote:
>
> This commit add tcache support in calloc() which can largely improve
> the performance of small size allocation, especially in multi-thread
> scenario. tcache_available() and tcache_try_malloc() are split out as
> a helper function for better reusing the code.
>
> Also fix tst-safe-linking failure after enabling tcache. In previous,
> calloc() is used as a way to by-pass tcache in memory allocation and
> trigger safe-linking check in fastbins path. With tcache enabled, it
> needs extra workarounds to bypass tcache.
>
> Result of bench-calloc-thread benchmark
>
> Test Platform: Xeon-8380
> Ratio: New / Original time_per_iteration (Lower is Better)
>
> Threads# | Ratio
> -----------|------
> 1 thread | 0.656
> 4 threads | 0.470
>
> ---
> Changes in v6:
> - Split out tcache_try_malloc()
> - Link to v5: https://sourceware.org/pipermail/libc-alpha/2024-December/162000.html
> Changes in v5:
> - Spelling fix: tcache_availabe -> tcache_available
> - Rebase to latest code base.
> - Link to v4: https://sourceware.org/pipermail/libc-alpha/2024-November/161738.html
> No Changes in v4.
> Changes in v3:
> - Split out tcache_available() as helper function.
> - Link to v2: https://sourceware.org/pipermail/libc-alpha/2024-August/159430.html
> Changes in v2:
> - Merge tst-safe-linking fix to make sure CI check pass.
> - Link to v1: https://sourceware.org/pipermail/libc-alpha/2024-August/159362.html
> ---
> malloc/malloc.c | 89 ++++++++++++++++++++++++++++-----------
> malloc/tst-safe-linking.c | 81 +++++++++++++++++++++++++++++------
> 2 files changed, 132 insertions(+), 38 deletions(-)
>
> diff --git a/malloc/malloc.c b/malloc/malloc.c
> index ac3901bdd5..f16f89d283 100644
> --- a/malloc/malloc.c
> +++ b/malloc/malloc.c
> @@ -3208,6 +3208,18 @@ tcache_next (tcache_entry *e)
> return (tcache_entry *) REVEAL_PTR (e->next);
> }
>
> +/* Check if tcache is available for alloc by corresponding tc_idx. */
> +static __always_inline bool
> +tcache_available (size_t tc_idx)
> +{
> + if (tc_idx < mp_.tcache_bins
> + && tcache != NULL
> + && tcache->counts[tc_idx] > 0)
> + return true;
> + else
> + return false;
> +}
> +
> /* Verify if the suspicious tcache_entry is double free.
> It's not expected to execute very often, mark it as noinline. */
> static __attribute__ ((noinline)) void
> @@ -3330,6 +3342,32 @@ tcache_init(void)
> if (__glibc_unlikely (tcache == NULL)) \
> tcache_init();
>
> +/* Trying to alloc BYTES from tcache. If tcache is available, chunk
> + is allocated and stored to MEMPTR, otherwise, MEMPTR is NULL.
> + It returns true if error occurs, else false. */
> +static __always_inline bool
> +tcache_try_malloc (size_t bytes, void **memptr)
> +{
> + /* int_free also calls request2size, be careful to not pad twice. */
> + size_t tbytes = checked_request2size (bytes);
> + if (tbytes == 0)
> + {
> + __set_errno (ENOMEM);
> + return true;
> + }
> +
> + size_t tc_idx = csize2tidx (tbytes);
> +
> + MAYBE_INIT_TCACHE ();
> +
> + if (tcache_available (tc_idx))
> + *memptr = tcache_get (tc_idx);
> + else
> + *memptr = NULL;
> +
> + return false;
> +}
> +
> #else /* !USE_TCACHE */
> # define MAYBE_INIT_TCACHE()
>
> @@ -3354,26 +3392,13 @@ __libc_malloc (size_t bytes)
> if (!__malloc_initialized)
> ptmalloc_init ();
> #if USE_TCACHE
> - /* int_free also calls request2size, be careful to not pad twice. */
> - size_t tbytes = checked_request2size (bytes);
> - if (tbytes == 0)
> - {
> - __set_errno (ENOMEM);
> - return NULL;
> - }
> - size_t tc_idx = csize2tidx (tbytes);
> + bool err = tcache_try_malloc (bytes, &victim);
>
> - MAYBE_INIT_TCACHE ();
> + if (err)
> + return NULL;
>
> - DIAG_PUSH_NEEDS_COMMENT;
> - if (tc_idx < mp_.tcache_bins
> - && tcache != NULL
> - && tcache->counts[tc_idx] > 0)
> - {
> - victim = tcache_get (tc_idx);
> + if (victim)
> return tag_new_usable (victim);
> - }
> - DIAG_POP_NEEDS_COMMENT;
> #endif
>
> if (SINGLE_THREAD_P)
> @@ -3667,9 +3692,7 @@ _mid_memalign (size_t alignment, size_t bytes, void *address)
> }
> size_t tc_idx = csize2tidx (tbytes);
>
> - if (tc_idx < mp_.tcache_bins
> - && tcache != NULL
> - && tcache->counts[tc_idx] > 0)
> + if (tcache_available (tc_idx))
> {
> /* The tcache itself isn't encoded, but the chain is. */
> tcache_entry **tep = & tcache->entries[tc_idx];
> @@ -3751,8 +3774,8 @@ void *
> __libc_calloc (size_t n, size_t elem_size)
> {
> mstate av;
> - mchunkptr oldtop;
> - INTERNAL_SIZE_T sz, oldtopsize;
> + mchunkptr oldtop, p;
> + INTERNAL_SIZE_T sz, oldtopsize, csz;
> void *mem;
> unsigned long clearsize;
> ptrdiff_t bytes;
> @@ -3768,7 +3791,23 @@ __libc_calloc (size_t n, size_t elem_size)
> if (!__malloc_initialized)
> ptmalloc_init ();
>
> - MAYBE_INIT_TCACHE ();
> +#if USE_TCACHE
> + bool err = tcache_try_malloc (bytes, &mem);
> +
> + if (err)
> + return NULL;
> +
> + if (mem)
> + {
> + p = mem2chunk (mem);
> + if (__glibc_unlikely (mtag_enabled))
> + return tag_new_zero_region (mem, memsize (p));
> +
> + csz = chunksize (p);
> + clearsize = csz - SIZE_SZ;
> + return clear_memory ((INTERNAL_SIZE_T *) mem, clearsize);
> + }
> +#endif
>
> if (SINGLE_THREAD_P)
> av = &main_arena;
> @@ -3824,7 +3863,7 @@ __libc_calloc (size_t n, size_t elem_size)
> if (mem == NULL)
> return NULL;
>
> - mchunkptr p = mem2chunk (mem);
> + p = mem2chunk (mem);
>
> /* If we are using memory tagging, then we need to set the tags
> regardless of MORECORE_CLEARS, so we zero the whole block while
> @@ -3832,7 +3871,7 @@ __libc_calloc (size_t n, size_t elem_size)
> if (__glibc_unlikely (mtag_enabled))
> return tag_new_zero_region (mem, memsize (p));
>
> - INTERNAL_SIZE_T csz = chunksize (p);
> + csz = chunksize (p);
>
> /* Two optional cases in which clearing not necessary */
> if (chunk_is_mmapped (p))
> diff --git a/malloc/tst-safe-linking.c b/malloc/tst-safe-linking.c
> index 01dd07004d..5302575ad1 100644
> --- a/malloc/tst-safe-linking.c
> +++ b/malloc/tst-safe-linking.c
> @@ -111,22 +111,37 @@ test_fastbin (void *closure)
> int i;
> int mask = ((int *)closure)[0];
> size_t size = TCACHE_ALLOC_SIZE;
> + void * ps[TCACHE_FILL_COUNT];
> + void * pps[TCACHE_FILL_COUNT];
>
> printf ("++ fastbin ++\n");
>
> + /* Populate the fastbin list. */
> + void * volatile a = calloc (1, size);
> + void * volatile b = calloc (1, size);
> + void * volatile c = calloc (1, size);
> + printf ("a=%p, b=%p, c=%p\n", a, b, c);
> +
> + /* Chunks for later tcache filling from fastbins. */
> + for (i = 0; i < TCACHE_FILL_COUNT; ++i)
> + {
> + void * volatile p = calloc (1, size);
> + pps[i] = p;
> + }
> +
> /* Take the tcache out of the game. */
> for (i = 0; i < TCACHE_FILL_COUNT; ++i)
> {
> void * volatile p = calloc (1, size);
> - printf ("p=%p\n", p);
> - free (p);
> + ps[i] = p;
> }
>
> - /* Populate the fastbin list. */
> - void * volatile a = calloc (1, size);
> - void * volatile b = calloc (1, size);
> - void * volatile c = calloc (1, size);
> - printf ("a=%p, b=%p, c=%p\n", a, b, c);
> + for (i = 0; i < TCACHE_FILL_COUNT; ++i)
> + {
> + free (ps[i]);
> + }
> +
> + /* Free abc will return to fastbin in FIFO order. */
> free (a);
> free (b);
> free (c);
> @@ -136,11 +151,43 @@ test_fastbin (void *closure)
> memset (c, mask & 0xFF, size);
> printf ("After: c=%p, c[0]=%p\n", c, ((void **)c)[0]);
>
> + /* Filling fastbins, will be copied to tcache later. */
> + for (i = 0; i < TCACHE_FILL_COUNT; ++i)
> + {
> + free (pps[i]);
> + }
> +
> + /* Drain out tcache to make sure later alloc from fastbins. */
> + for (i = 0; i < TCACHE_FILL_COUNT; ++i)
> + {
> + void * volatile p = calloc (1, size);
> + ps[i] = p;
> + }
> +
> + /* This line will also filling tcache with remain pps and c. */
> + pps[TCACHE_FILL_COUNT - 1] = calloc (1, size);
> +
> + /* Tcache is FILO, now the first one is c, take it out. */
> c = calloc (1, size);
> printf ("Allocated: c=%p\n", c);
> +
> + /* Drain out remain pps from tcache. */
> + for (i = 0; i < TCACHE_FILL_COUNT - 1; ++i)
> + {
> + void * volatile p = calloc (1, size);
> + pps[i] = p;
> + }
> +
> /* This line will trigger the Safe-Linking check. */
> b = calloc (1, size);
> printf ("b=%p\n", b);
> +
> + /* Free previous pointers. */
> + for (i = 0; i < TCACHE_FILL_COUNT; ++i)
> + {
> + free (ps[i]);
> + free (pps[i]);
> + }
> }
>
> /* Try corrupting the fastbin list and trigger a consolidate. */
> @@ -150,21 +197,29 @@ test_fastbin_consolidate (void *closure)
> int i;
> int mask = ((int*)closure)[0];
> size_t size = TCACHE_ALLOC_SIZE;
> + void * ps[TCACHE_FILL_COUNT];
>
> printf ("++ fastbin consolidate ++\n");
>
> + /* Populate the fastbin list. */
> + void * volatile a = calloc (1, size);
> + void * volatile b = calloc (1, size);
> + void * volatile c = calloc (1, size);
> + printf ("a=%p, b=%p, c=%p\n", a, b, c);
> +
> /* Take the tcache out of the game. */
> for (i = 0; i < TCACHE_FILL_COUNT; ++i)
> {
> void * volatile p = calloc (1, size);
> - free (p);
> + ps[i] = p;
> }
>
> - /* Populate the fastbin list. */
> - void * volatile a = calloc (1, size);
> - void * volatile b = calloc (1, size);
> - void * volatile c = calloc (1, size);
> - printf ("a=%p, b=%p, c=%p\n", a, b, c);
> + for (i = 0; i < TCACHE_FILL_COUNT; ++i)
> + {
> + free (ps[i]);
> + }
> +
> + /* Free abc will return to fastbin. */
> free (a);
> free (b);
> free (c);
> --
> 2.43.5
>
LGTM.
Reviewed-by: H.J. Lu <hjl.tools@gmail.com>
Thanks.
--
H.J.
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