[PATCH] mm: fix adaptive hash table sizing for 32b systems

[Michal Hocko]

Guenter Roeck has noticed that many qemu boot test on 32b systems
and bisected it to "mm: drop HASH_ADAPT". The patch itself only
makes the HASH_ADAPT unconditional for all users which shouldn't
matter. Except it does because ADAPT_SCALE_BASE is 64GB which is
out of 32b word size so the adapt_scale loop will never terminate
and so HASH_EARLY allocations lock up with the patch while we even
do not try to use the new hash adapt code because the early allocation
suceeded.

Fix this by reducint ADAPT_SCALE_BASE down to 32MB on 32b machines.

Fixes: mm: adaptive hash table scaling
Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
---
 mm/page_alloc.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index a26e19c3e1ff..70c5fc1fb89a 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -7174,11 +7174,15 @@ static unsigned long __init arch_reserved_kernel_pages(void)
 /*
  * Adaptive scale is meant to reduce sizes of hash tables on large memory
  * machines. As memory size is increased the scale is also increased but at
- * slower pace.  Starting from ADAPT_SCALE_BASE (64G), every time memory
- * quadruples the scale is increased by one, which means the size of hash table
- * only doubles, instead of quadrupling as well.
+ * slower pace.  Starting from ADAPT_SCALE_BASE (64G on 64b systems and 32M
+ * on 32b), every time memory quadruples the scale is increased by one, which
+ * means the size of hash table only doubles, instead of quadrupling as well.
  */
+#if __BITS_PER_LONG == 64
 #define ADAPT_SCALE_BASE	(64ul << 30)
+#else
+#define ADAPT_SCALE_BASE	(32ul << 20)
+#endif
 #define ADAPT_SCALE_SHIFT	2
 #define ADAPT_SCALE_NPAGES	(ADAPT_SCALE_BASE >> PAGE_SHIFT)
 
-- 
2.11.0

-- 
Michal Hocko
SUSE Labs