[PATCH v2] mm/huge_memory.c: disable THP with large THP size on small present memory

[Hao Peng <flyingpenghao@gmail.com>]

From: Peng Hao <flyingpeng@tencent.com>

After setting the page size to 64k on ARM64, the supported huge page
size is 512M and 1TB. Therefore, if the thp is enabled, the size
of the thp is 512M. But if THP is enabled, min_free_kbytes will
be recalculated. At this time, min_free_kbytes is calculated based
on the size of THP.

On an arm64 server with 64G memory, the page size is 64k, with thp
enabled.
cat /proc/sys/vm/min_free_kbytes
3335104

Therefore, when judging whether to enable THP by default, consider
the size of thp.

V2: title suggested by David Hildenbrand

Signed-off-by: Peng Hao <flyingpeng@tencent.com>
---
 mm/huge_memory.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 5e9ef0fc261e..03c7f571b3ae 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -437,7 +437,7 @@ static int __init hugepage_init(void)
         * where the extra memory used could hurt more than TLB overhead
         * is likely to save.  The admin can still enable it through /sys.
         */
-       if (totalram_pages() < (512 << (20 - PAGE_SHIFT))) {
+       if (totalram_pages() < (512 << (HPAGE_PMD_SHIFT - PAGE_SHIFT))) {
                transparent_hugepage_flags = 0;
                return 0;
        }
--
2.27.0