netdev - Re: [net-next rfc 1/3] net: avoid high order memory allocation for queues by using flex array

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Wed, 19 Jun 2013 02:56:03 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	Jason Wang <jasowang@...hat.com>, davem@...emloft.net,
	edumazet@...gle.com, hkchu@...gle.com, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [net-next rfc 1/3] net: avoid high order memory allocation for
 queues by using flex array

On Wed, 2013-06-19 at 12:11 +0300, Michael S. Tsirkin wrote:

> Well KVM supports up to 160 VCPUs on x86.
> 
> Creating a queue per CPU is very reasonable, and
> assuming cache line size of 64 bytes, netdev_queue seems to be 320
> bytes, that's 320*160 = 51200. So 12.5 pages, order-4 allocation.
> I agree most people don't have such systems yet, but
> they do exist.

Even so, it will just work, like a fork() is likely to work, even if a
process needs order-1 allocation for kernel stack.

Some drivers still use order-10 allocations with kmalloc(), and nobody
complained yet.

We had complains with mlx4 driver lately only bcause kmalloc() now gives
a warning if allocations above MAX_ORDER are attempted.

Having a single pointer means that we can :

- Attempts a regular kmalloc() call, it will work most of the time.
- fallback to vmalloc() _if_ kmalloc() failed.

Frankly, if you want one tx queue per cpu, I would rather use
NETIF_F_LLTX, like some other virtual devices.

This way, you can have real per cpu memory, with proper NUMA affinity.

--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html