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

From: Stephen Hemminger <[email-masked]>
Date: Tue, 14 Dec 2010 14:23:20 -0800

On Tue, 14 Dec 2010 23:35:37 +0300
Vladislav Bolkhovitin <[email-masked]> 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.

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