Subject: [RFC PATCH 1/5] mm: large system hash use vmalloc for size > MAX_ORDER when !hashdist

From: Nicholas Piggin <[email-masked]>
Date: Wed, 15 May 2019 23:19:40 +1000

The kernel currently clamps large system hashes to MAX_ORDER when
hashdist is not set, which is rather arbitrary.

vmalloc space is limited on 32-bit machines, but this shouldn't
result in much more used because of small physical memory.

Signed-off-by: Nicholas Piggin <[email-masked]>
---
 mm/page_alloc.c | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 59661106da16..1683d54d6405 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -7978,7 +7978,7 @@ void *__init alloc_large_system_hash(const char *tablename,
 			else
 				table = memblock_alloc_raw(size,
 							   SMP_CACHE_BYTES);
-		} else if (hashdist) {
+		} else if (get_order(size) >= MAX_ORDER || hashdist) {
 			table = __vmalloc(size, gfp_flags, PAGE_KERNEL);
 		} else {
 			/*
@@ -7986,10 +7986,8 @@ void *__init alloc_large_system_hash(const char *tablename,
 			 * some pages at the end of hash table which
 			 * alloc_pages_exact() automatically does
 			 */
-			if (get_order(size) < MAX_ORDER) {
-				table = alloc_pages_exact(size, gfp_flags);
-				kmemleak_alloc(table, size, 1, gfp_flags);
-			}
+			table = alloc_pages_exact(size, gfp_flags);
+			kmemleak_alloc(table, size, 1, gfp_flags);
 		}
 	} while (!table && size > PAGE_SIZE && --log2qty);
 
-- 
2.20.1