[PATCH 0/2] net: Replace custom page based bitmap with IDA

From: Tobin C. Harding
Date: Sat Feb 11 2017 - 21:58:13 EST

Current implementation of __dev_alloc_name uses a custom bitmap of
a single page to iterate network device id's and allocate an
unused id. This is seemingly the same task that the IDA does. Also the
current implementation leads to a upper limit of 8 * PAGE_SIZE on the
number of network id's (for each name format i.e eth0).

This patch uses the kernel's IDA as a replacement to the page based
bitmap. This has the effect of simplifying the code and removing
the upper limit.

Testing was carried out using a simple network device module, the
core of which is;

#define NDEVICES 32768 /* current implementation hard limit */

/* test driver */
static int tm_init_module(void)
int result;
int i;
unsigned long before, after, diff, msec;

pr_debug("tm: init module");

before = jiffies;

for (i = 0; i < NDEVICES; i++) {

devs[i] = alloc_netdev(0, "sn%d",

if (!devs[i])
return -ENOMEM;

result = register_netdev(devs[i]);
if (result) {
pr_err("tm: error %i registering device \"%s\"\n",
result, devs[i]->name);
return -ENODEV;

after = jiffies;
diff = (long)after - (long)before;
msec = diff * 1000 / HZ;
pr_debug("tm: Total milliseconds: %ld\n", msec);

return 0;

The main objective of this patch is to simplify the code of __dev_alloc_name.
As a side effect the hard limit is also removed. Results from running the,
admittedly convoluted, test module show that the patched version is slightly slower.


System: core i5 Linux 4.10.0-rc7+ #18 SMP

$ qemu-system-x86_64 -kernel arch/x86_64/boot/bzImage -drive file=/home/tobin/build/imgs/qemu-image.img,index=0,media=disk,format=raw -append "root=/dev/sda console=ttyS0" --enable-kvm --nographic -m 12G

Current implementation

#define NDEVICES 30000

[ 134.376741] tm: Total milliseconds: 127152

Patched version

#define NDEVICES 30000

[ 226.960212] tm: Total milliseconds: 220756

#define NDEVICES 35000

[ 276.590994] tm: Total milliseconds: 270620

Tobin C. Harding (2):
include: Fix checkpatch whitespace error and warning
net: Replace custom page based bitmap with IDA

include/linux/idr.h | 4 ++--
net/core/dev.c | 20 ++++++--------------
2 files changed, 8 insertions(+), 16 deletions(-)