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* [glibc] malloc: Improve MAP_HUGETLB with glibc.malloc.hugetlb=2
@ 2023-11-29 12:31 Adhemerval Zanella
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From: Adhemerval Zanella @ 2023-11-29 12:31 UTC (permalink / raw)
To: glibc-cvs
https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=bc6d79f4ae99206e7ec7d6a8c5abf26cdefc8bff
commit bc6d79f4ae99206e7ec7d6a8c5abf26cdefc8bff
Author: Adhemerval Zanella <adhemerval.zanella@linaro.org>
Date: Thu Nov 23 14:29:15 2023 -0300
malloc: Improve MAP_HUGETLB with glibc.malloc.hugetlb=2
Even for explicit large page support, allocation might use mmap without
the hugepage bit set if the requested size is smaller than
mmap_threshold. For this case where mmap is issued, MAP_HUGETLB is set
iff the allocation size is larger than the used large page.
To force such allocations to use large pages, also tune the mmap_threhold
(if it is not explicit set by a tunable). This forces allocation to
follow the sbrk path, which will fall back to mmap (which will try large
pages before galling back to default mmap).
Checked on x86_64-linux-gnu.
Reviewed-by: DJ Delorie <dj@redhat.com>
Tested-by: Zhangfei Gao <zhangfei.gao@linaro.org>
Diff:
---
malloc/arena.c | 13 ++++++++++---
1 file changed, 10 insertions(+), 3 deletions(-)
diff --git a/malloc/arena.c b/malloc/arena.c
index a1a75e5a2b..c73f68890d 100644
--- a/malloc/arena.c
+++ b/malloc/arena.c
@@ -312,10 +312,17 @@ ptmalloc_init (void)
# endif
TUNABLE_GET (mxfast, size_t, TUNABLE_CALLBACK (set_mxfast));
TUNABLE_GET (hugetlb, size_t, TUNABLE_CALLBACK (set_hugetlb));
+
if (mp_.hp_pagesize > 0)
- /* Force mmap for main arena instead of sbrk, so hugepages are explicitly
- used. */
- __always_fail_morecore = true;
+ {
+ /* Force mmap for main arena instead of sbrk, so MAP_HUGETLB is always
+ tried. Also tune the mmap threshold, so allocation smaller than the
+ large page will also try to use large pages by falling back
+ to sysmalloc_mmap_fallback on sysmalloc. */
+ if (!TUNABLE_IS_INITIALIZED (mmap_threshold))
+ do_set_mmap_threshold (mp_.hp_pagesize);
+ __always_fail_morecore = true;
+ }
}
/* Managing heaps and arenas (for concurrent threads) */
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