Re: After memory pressure: can't read from tape anymore

[Vladislav Bolkhovitin <vst@vlnb.net>]

Stephen Hemminger, on 12/15/2010 01:23 AM wrote:
> On Tue, 14 Dec 2010 23:35:37 +0300
> Vladislav Bolkhovitin <vst@vlnb.net> wrote:
> 
>> What is interesting to me in this regard is how networking with 9K jumbo
>> frames manages to work acceptably reliable? Jumbo frames used
>> sufficiently often, including under high memory pressure.
>>
>> I'm not a deep networking guru, but network drivers need to allocate
>> physically continual memory for skbs, which means 16K per 9K packet,
>> which means order 2 allocations per skb.
> 
> Good network drivers support fragmentation and allocate a small portion
> for the header and allocate pages for the rest. This requires no higher
> order allocation. The networking stack takes fragmented data coming
> in and does the necessary copy/merging to access contiguous headers.
> 
> There are still some crap network drivers that require large contiguous
> allocation. These should not be used with jumbo frames in real
> environments.

I see. Thanks for clarifying it.

Vlad