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malloc: Enable THP always support on hugetlb tunable 

Enable support for THP always when glibc.malloc.hugetlb=1, as the tunable
currently only gives explicit support in malloc for the THP madvise mode
by aligning to a huge page size. Add a thp_mode parameter to mp_ and check
in madvise_thp whether the system is using madvise mode, otherwise the
`__madvise` call is useless. Set the thp_mode to be unsupported by default,
but if the hugetlb tunable is set this updates thp_mode. Performance of
xalancbmk improves by 4.9% on Neoverse V2 when THP always mode is set on the
system and glibc.malloc.hugetlb=1.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>
This commit is contained in:
William Hunt 2025-07-29 15:04:58 +00:00 committed by Wilco Dijkstra
parent 089b4fb90f
commit 9097cbf5d8
1 changed files with 11 additions and 7 deletions
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18
malloc/malloc.c
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@ -1871,6 +1871,7 @@ struct malloc_par
INTERNAL_SIZE_T arena_max;
/* Transparent Large Page support. */
enum malloc_thp_mode_t thp_mode;
INTERNAL_SIZE_T thp_pagesize;
/* A value different than 0 means to align mmap allocation to hp_pagesize
add hp_flags on flags. */
@ -1927,7 +1928,8 @@ static struct malloc_par mp_ =
.mmap_threshold = DEFAULT_MMAP_THRESHOLD,
.trim_threshold = DEFAULT_TRIM_THRESHOLD,
#define NARENAS_FROM_NCORES(n) ((n) * (sizeof (long) == 4 ? 2 : 8))
.arena_test = NARENAS_FROM_NCORES (1)
.arena_test = NARENAS_FROM_NCORES (1),
.thp_mode = malloc_thp_mode_not_supported
#if USE_TCACHE
,
.tcache_count = TCACHE_FILL_COUNT,
@ -2011,6 +2013,11 @@ static inline void
madvise_thp (void *p, INTERNAL_SIZE_T size)
{
#ifdef MADV_HUGEPAGE
/* Only use __madvise if the system is using 'madvise' mode.
Otherwise the call is wasteful. */
if (mp_.thp_mode != malloc_thp_mode_madvise)
return;
/* Do not consider areas smaller than a huge page or if the tunable is
not active. */
if (mp_.thp_pagesize == 0 || size < mp_.thp_pagesize)
@ -5648,12 +5655,9 @@ do_set_hugetlb (size_t value)
{
if (value == 1)
{
enum malloc_thp_mode_t thp_mode = __malloc_thp_mode ();
/*
Only enable THP madvise usage if system does support it and
has 'madvise' mode. Otherwise the madvise() call is wasteful.
*/
if (thp_mode == malloc_thp_mode_madvise)
mp_.thp_mode = __malloc_thp_mode ();
if (mp_.thp_mode == malloc_thp_mode_madvise
|| mp_.thp_mode == malloc_thp_mode_always)
mp_.thp_pagesize = __malloc_default_thp_pagesize ();
}
else if (value >= 2)