Re: iwl3945: order 5 allocation during ifconfig up; vm problem?

On Tue, Sep 11, 2012 at 04:25:36PM -0700, Andrew Morton wrote:

On Mon, 10 Sep 2012 13:11:13 +0200
Pavel Machek [off-list ref] wrote:

quoted

On Sun 2012-09-09 15:40:55, David Rientjes wrote:

quoted

On Sun, 9 Sep 2012, Pavel Machek wrote:

quoted

On 3.6.0-rc2+, I tried to turn on the wireless, but got

root@amd:~# ifconfig wlan0 10.0.0.6 up
SIOCSIFFLAGS: Cannot allocate memory
SIOCSIFFLAGS: Cannot allocate memory
root@amd:~# 

It looks like it uses "a bit too big" allocations to allocate
firmware...? Order five allocation....

Hmm... then I did "echo 3  > /proc/sys/vm/drop_caches" and now the
network works. Is it VM problem that it failed to allocate memory when
it was freeable?

Do you have CONFIG_COMPACTION enabled?

Yes:

pavel@amd:/data/l/linux-good$ zgrep CONFIG_COMPACTION /proc/config.gz 
CONFIG_COMPACTION=y

Asking for a 256k allocation is pretty crazy - this is an operating
system kernel, not a userspace application.

I'm wondering if this is due to a recent change, but I'm having trouble
working out where the allocation call site is.

It may be indirectly due to a recent change and this was somewhat
deliberate. Order-5 is larger than PAGE_ALLOC_COSTLY_ORDER and I doubt
__GFP_REPEAT was set so it is treated as something that can fail in
preference to aggressively reclaiming pages to satisfy the allocation. In
older kernels with lumpy reclaim and an aggressive kswapd it would have
probably succeeded but now it errs on the side of failing early instead
assuming that the caller can recover. Drivers that depend on order-5
allocations to succeed for correct operation are somewhat frowned upon.

-- 
Mel Gorman
SUSE Labs