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From: Adhemerval Zanella <azanella@sourceware.org> To: glibc-cvs@sourceware.org Subject: [glibc] malloc: Improve MAP_HUGETLB with glibc.malloc.hugetlb=2 Date: Wed, 29 Nov 2023 12:31:13 +0000 (GMT) [thread overview] Message-ID: <20231129123113.51E0D3858005@sourceware.org> (raw) 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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