From b0ce6fa8bd3c171debd5589f3ee8a95e26b1d61b Mon Sep 17 00:00:00 2001
From: notaz <notasas@gmail.com>
Date: Mon, 2 Oct 2023 01:27:58 +0300
Subject: [PATCH] plat: add a thp-based huge page fallback

unlike MAP_HUGETLB it's often enabled in distros by default
---
 linux/plat.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/linux/plat.c b/linux/plat.c
index 707d5f7..b1c3314 100644
--- a/linux/plat.c
+++ b/linux/plat.c
@@ -13,6 +13,7 @@
 #include <stdio.h>
 #include <string.h>
 #include <stdarg.h>
+#include <stdint.h>
 #include <dirent.h>
 #include <sys/time.h>
 #include <time.h>
@@ -207,6 +208,16 @@ void *plat_mmap(unsigned long addr, size_t size, int need_exec, int is_fixed)
 		}
 		flags &= ~MAP_HUGETLB;
 		ret = mmap(req, size, prot, flags, -1, 0);
+#ifdef MADV_HUGEPAGE
+		if (ret != MAP_FAILED && ((uintptr_t)ret & (2*1024*1024 - 1))) {
+			// try to manually realign assuming bottom-to-top alloc
+			munmap(ret, size);
+			ret = (void *)((uintptr_t)ret & ~(2*1024*1024 - 1));
+			ret = mmap(ret, size, prot, flags, -1, 0);
+		}
+		if (ret != MAP_FAILED)
+			madvise(ret, size, MADV_HUGEPAGE);
+#endif
 	}
 	if (ret == MAP_FAILED)
 		return NULL;
-- 
2.39.5