Re: [E1000-devel] Page Allocation Failure with e1000 using jumbo frame

[Michael Iatrou <m.iatrou@freemail.gr>]

When the date was Friday 19 August 2005 19:51, Jesse Brandeburg wrote:

> included netdev...
>
> On Wed, 17 Aug 2005, Ming Zhang wrote:
> > Hi folks
> >
> > We ran into this problem when running jumbo frame with iscsi over e1000.
> > the MTU1500 is fine while jumbo frame can stably reproduce this error.
> >
> > when meet this error, as reported in iet list, the box still has >600MB
> > ram free. also the slab is not heavily used.
> >
> > any idea on this?
>
> So, what we do know is that your kernel memory manager is (for whatever
> unknown reason) having trouble finding contiguous 2^3 pages (32kB) chunks
> of memory.  This occurs because we need to give our hardware 16kB
> contiguous (currently, we actually have a patch for this in internal
> testing) which means that when we do dev_alloc_skb, it allocates 16kB + 16
> bytes reserve, plus 2 bytes NET_IP_ALIGN, which takes us into the 32kB
> slab (power of two roundup)

I don't get it: For MTU = 9000, you already have to allocate 2^3 pages, but 
testing shows that the problem only occurs for MTU > 3*PAGE_SIZE

http://members.hellug.gr/iatrou/plain_ip_mtu.png

(reference to previous discussion)
http://sourceforge.net/mailarchive/forum.php?forum_id=12401&max_rows=25&style=ultimate&viewmonth=200505

-- 
 Michael Iatrou
 Electrical and Computer Engineering Dept.
 University of Patras, Greece


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