Re: 2.6.17: networking bug??

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Mark Lord wrote:
..
The site www.everymac.com is still not browseable until
setting /proc/sys/net/ipv4/tcp_window_scaling===0.

There's one other difference I see in the tcpdump traces.
The first packets from each trace below show different
values for "wscale".  The old (working) kernels use "wscale 2",
whereas 2.6.17 uses "wscale 6".  In both cases, the value
seen in /proc/sys/net/ipv4/tcp_adv_win_scale is 2.

Okay.  More progress here.  The calculation of the "wscale" values
is based on the "tcp_rmem" sysctl numbers.

The defaults for these *differ* between 2.6.16.18 and 2.6.17-rc*.

2.6.16: 4096    87380    174760
2.6.17: 4096    87380   2097152

If I change the tcp_rmem setting on 2.6.17 to match the old value,
then the website www.everymac.com becomes accessible again:

echo 4096 87380 174760 > /proc/sys/net/ipv4/tcp_rmem

Looking at diffs between 2.6.16 and 2.6.17, I see a big rework
of the tcp_rmem code in linux/net/ipv4/tcp.c

Looks like something got broken there, or possibly the wscale
calculations have a bug that is only triggered by the new rmem values ??


Okay, here's the blob that broke it.

[TCP]: Set default max buffers from memory pool size
author	John Heffner <[email protected]>
	Sat, 25 Mar 2006 09:34:07 +0000 (01:34 -0800)
committer	David S. Miller <[email protected]>
	Sat, 25 Mar 2006 09:34:07 +0000 (01:34 -0800)
commit	7b4f4b5ebceab67ce440a61081a69f0265e17c2a
tree	ac02c685ce23f2440fecbebaa5b55cd47947c03e	tree
parent	2babf9daae4a3561f3264638a22ac7d0b14a6f52	commit | commitdiff
[TCP]: Set default max buffers from memory pool size

This patch sets the maximum TCP buffer sizes (available to automatic
buffer tuning, not to setsockopt) based on the TCP memory pool size.
The maximum sndbuf and rcvbuf each will be up to 4 MB, but no more
than 1/128 of the memory pressure threshold.

Signed-off-by: John Heffner <[email protected]>
Signed-off-by: David S. Miller <[email protected]>

John / David:  Any ideas on what's gone awry here?



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