RE: [PATCH for-next 03/11] IB/hns: Optimize the logic of allocating memory using APIs

-----Original Message-----
From: Leon Romanovsky [mailto:leon@kernel.org]
Sent: Wednesday, November 09, 2016 7:22 AM
To: Salil Mehta
Cc: dledford@redhat.com; Huwei (Xavier); oulijun;
mehta.salil.lnk@gmail.com; linux-rdma@vger.kernel.org;
netdev@vger.kernel.org; linux-kernel@vger.kernel.org; Linuxarm;
Zhangping (ZP)
Subject: Re: [PATCH for-next 03/11] IB/hns: Optimize the logic of
allocating memory using APIs

On Fri, Nov 04, 2016 at 04:36:25PM +0000, Salil Mehta wrote:

quoted

From: "Wei Hu (Xavier)" <redacted>

This patch modified the logic of allocating memory using APIs in
hns RoCE driver. We used kcalloc instead of kmalloc_array and
bitmap_zero. And When kcalloc failed, call vzalloc to alloc
memory.

Signed-off-by: Wei Hu (Xavier) <redacted>
Signed-off-by: Ping Zhang <redacted>
Signed-off-by: Salil Mehta  <redacted>
---
 drivers/infiniband/hw/hns/hns_roce_mr.c |   15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/drivers/infiniband/hw/hns/hns_roce_mr.c

b/drivers/infiniband/hw/hns/hns_roce_mr.c

quoted

index fb87883..d3dfb5f 100644

--- a/drivers/infiniband/hw/hns/hns_roce_mr.c
+++ b/drivers/infiniband/hw/hns/hns_roce_mr.c

@@ -137,11 +137,12 @@ static int hns_roce_buddy_init(struct

hns_roce_buddy *buddy, int max_order)

quoted

 	for (i = 0; i <= buddy->max_order; ++i) {
 		s = BITS_TO_LONGS(1 << (buddy->max_order - i));
-		buddy->bits[i] = kmalloc_array(s, sizeof(long),

GFP_KERNEL);

quoted

-		if (!buddy->bits[i])
-			goto err_out_free;
-
-		bitmap_zero(buddy->bits[i], 1 << (buddy->max_order - i));
+		buddy->bits[i] = kcalloc(s, sizeof(long), GFP_KERNEL);
+		if (!buddy->bits[i]) {
+			buddy->bits[i] = vzalloc(s * sizeof(long));

I wonder, why don't you use directly vzalloc instead of kcalloc
fallback?

As we know we will have physical contiguous pages if the kcalloc
call succeeds. This will give us a chance to have better performance
over the allocations which are just virtually contiguous through the
function vzalloc(). Therefore, later has only been used as a fallback
when our memory request cannot be entertained through kcalloc.

Are you suggesting that there will not be much performance penalty
if we use just vzalloc ?

quoted

+			if (!buddy->bits[i])
+				goto err_out_free;
+		}
 	}