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malloc: Improve arena_for_chunk()

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Change heap_max_size() to improve performance of arena_for_chunk().
Instead of a complex calculation, using a simple mask operation to get the
arena base pointer.  HEAP_MAX_SIZE should be larger than the huge page size,
otherwise heaps will use not huge pages.

On AArch64 this removes 6 instructions from arena_for_chunk(), and
bench-malloc-thread improves by 1.1% - 1.8%.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>
This commit is contained in:
Wilco Dijkstra
2025-03-18 12:30:10 +00:00
parent dd003db8d1
commit 9f551e28a7
1 changed files with 7 additions and 6 deletions
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13
malloc/arena.c
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@@ -40,19 +40,20 @@
mmap threshold, so that requests with a size just below that mmap threshold, so that requests with a size just below that
threshold can be fulfilled without creating too many heaps. */ threshold can be fulfilled without creating too many heaps. */
/* When huge pages are used to create new arenas, the maximum and minimum /* HEAP_MAX_SIZE should be larger than the huge page size, otherwise heaps will
size are based on the runtime defined huge page size. */ use not huge pages. It is a constant so arena_for_chunk() is efficient. */
static inline size_t static inline size_t
heap_min_size (void) heap_min_size (void)
{ {
return mp_.hp_pagesize == 0 ? HEAP_MIN_SIZE : mp_.hp_pagesize; return mp_.hp_pagesize == 0 || mp_.hp_pagesize > HEAP_MAX_SIZE
? HEAP_MIN_SIZE : mp_.hp_pagesize;
} }
static inline size_t static inline size_t
heap_max_size (void) heap_max_size (void)
{ {
return mp_.hp_pagesize == 0 ? HEAP_MAX_SIZE : mp_.hp_pagesize * 4; return HEAP_MAX_SIZE;
} }
/***************************************************************************/ /***************************************************************************/
@@ -313,7 +314,7 @@ ptmalloc_init (void)
TUNABLE_GET (mxfast, size_t, TUNABLE_CALLBACK (set_mxfast)); TUNABLE_GET (mxfast, size_t, TUNABLE_CALLBACK (set_mxfast));
TUNABLE_GET (hugetlb, size_t, TUNABLE_CALLBACK (set_hugetlb)); TUNABLE_GET (hugetlb, size_t, TUNABLE_CALLBACK (set_hugetlb));
if (mp_.hp_pagesize > 0) if (mp_.hp_pagesize > 0 && mp_.hp_pagesize <= heap_max_size ())
{ {
/* Force mmap for main arena instead of sbrk, so MAP_HUGETLB is always /* Force mmap for main arena instead of sbrk, so MAP_HUGETLB is always
tried. Also tune the mmap threshold, so allocation smaller than the tried. Also tune the mmap threshold, so allocation smaller than the
@@ -460,7 +461,7 @@ alloc_new_heap (size_t size, size_t top_pad, size_t pagesize,
static heap_info * static heap_info *
new_heap (size_t size, size_t top_pad) new_heap (size_t size, size_t top_pad)
{ {
if (__glibc_unlikely (mp_.hp_pagesize != 0)) if (mp_.hp_pagesize != 0 && mp_.hp_pagesize <= heap_max_size ())
{ {
heap_info *h = alloc_new_heap (size, top_pad, mp_.hp_pagesize, heap_info *h = alloc_new_heap (size, top_pad, mp_.hp_pagesize,
mp_.hp_flags); mp_.hp_flags);