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From bc6d79f4ae99206e7ec7d6a8c5abf26cdefc8bff Mon Sep 17 00:00:00 2001
From: Adhemerval Zanella <adhemerval.zanella@linaro.org>
Date: Thu, 23 Nov 2023 14:29:15 -0300
Subject: [PATCH] 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>
Conflict: this adapt the context from the origin commit.
---
malloc/arena.c | 12 +++++++++---
1 file changed, 9 insertions(+), 3 deletions(-)
diff --git a/malloc/arena.c b/malloc/arena.c
index f8e425e1..33dbc5ae 100644
--- a/malloc/arena.c
+++ b/malloc/arena.c
@@ -366,9 +366,15 @@ ptmalloc_init (void)
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;
+ }
#else
if (__glibc_likely (_environ != NULL))
{
--
2.33.0
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