netdev - Re: surprising memory request

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Date:	Fri, 18 Jan 2013 09:46:30 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Dirk Hohndel <dirk@...ndel.org>, Jason Wang <jasowang@...hat.com>
Cc:	netdev@...r.kernel.org, David Woodhouse <dwmw2@...radead.org>
Subject: Re: surprising memory request

On Fri, 2013-01-18 at 08:58 -0800, Dirk Hohndel wrote:
> Running openconnect on a very recent 3.8 (a few commits before Linus cut
> RC4) I get this allocation failure. I'm unclear why we would need 128
> contiguous pages here...
> 
> /D
> 
> [66015.673818] openconnect: page allocation failure: order:7, mode:0x10c0d0
> [66015.673827] Pid: 3292, comm: openconnect Tainted: G        W    3.8.0-rc3-00352-gdfdebc2 #94
> [66015.673830] Call Trace:
> [66015.673841]  [<ffffffff810e9c29>] warn_alloc_failed+0xe9/0x140
> [66015.673849]  [<ffffffff81093967>] ? on_each_cpu_mask+0x87/0xa0
> [66015.673854]  [<ffffffff810ec349>] __alloc_pages_nodemask+0x579/0x720
> [66015.673859]  [<ffffffff810ec507>] __get_free_pages+0x17/0x50
> [66015.673866]  [<ffffffff81123979>] kmalloc_order_trace+0x39/0xf0
> [66015.673874]  [<ffffffff81666178>] ? __hw_addr_add_ex+0x78/0xc0
> [66015.673879]  [<ffffffff811260d8>] __kmalloc+0xc8/0x180
> [66015.673883]  [<ffffffff81666616>] ? dev_addr_init+0x66/0x90
> [66015.673889]  [<ffffffff81660985>] alloc_netdev_mqs+0x145/0x300
> [66015.673896]  [<ffffffff81513830>] ? tun_net_fix_features+0x20/0x20
> [66015.673902]  [<ffffffff815168aa>] __tun_chr_ioctl+0xd0a/0xec0
> [66015.673908]  [<ffffffff81516a93>] tun_chr_ioctl+0x13/0x20
> [66015.673913]  [<ffffffff8113b197>] do_vfs_ioctl+0x97/0x530
> [66015.673917]  [<ffffffff811256f3>] ? kmem_cache_free+0x33/0x170
> [66015.673923]  [<ffffffff81134896>] ? final_putname+0x26/0x50
> [66015.673927]  [<ffffffff8113b6c1>] sys_ioctl+0x91/0xb0
> [66015.673935]  [<ffffffff8180e3d2>] system_call_fastpath+0x16/0x1b
> [66015.673938] Mem-Info:

Thats because Jason thought that tun device had to have an insane number
of queues to get good performance.

#define MAX_TAP_QUEUES 1024

Thats crazy if your machine has say 8 cpus.

And Jason didnt care to adapt the memory allocations done in
alloc_netdev_mqs(), in order to switch to vmalloc() when kmalloc()
fails.

commit c8d68e6be1c3b242f1c598595830890b65cea64a
Author: Jason Wang <jasowang@...hat.com>
Date:   Wed Oct 31 19:46:00 2012 +0000

    tuntap: multiqueue support
    
    This patch converts tun/tap to a multiqueue devices and expose the multiqueue
    queues as multiple file descriptors to userspace. Internally, each tun_file were
    abstracted as a queue, and an array of pointers to tun_file structurs were
    stored in tun_structure device, so multiple tun_files were allowed to be
    attached to the device as multiple queues.
    
    When choosing txq, we first try to identify a flow through its rxhash, if it
    does not have such one, we could try recorded rxq and then use them to choose
    the transmit queue. This policy may be changed in the future.
    
    Signed-off-by: Jason Wang <jasowang@...hat.com>
    Signed-off-by: David S. Miller <davem@...emloft.net>



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