[PATCH] tcp.7: Document removal of TCP_SYNQ_HSIZE

[PATCH] tcp.7: Document removal of TCP_SYNQ_HSIZE

[Peter Adkins]

Hello there,

Looking over the man page for 'tcp' I came across a reference to
tuning the 'TCP_SYNQ_HSIZE' parameter when increasing
'tcp_max_syn_backlog' above 1024. However, this static sizing was
removed back in Linux 2.6.20 in favour of dynamic scaling - as part of
commit 72a3effaf633bcae9034b7e176bdbd78d64a71db.

I have included a patch below with reference to this commit, and that
the process detailed is not required on >= Linux 2.6.20. This is my
first patch for a man page, as well as groff, so I apologize if
anything is incorrect. If so, please let me know and I will resolve
and resubmit.

This patch was prepared against the current HEAD - at time of writing
- from the Kernel.org man-page repository
(f6d086878485f63e390d10f59b6beae7b96c4120), which looks to be version
3.82.


---
 man7/tcp.7 | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/man7/tcp.7 b/man7/tcp.7
index 5723bde..794c636 100644
--- a/man7/tcp.7
+++ b/man7/tcp.7
@@ -530,12 +530,16 @@ The default value of 256 is increased to
 1024 when the memory present in the system is adequate or
 greater (>= 128Mb), and reduced to 128 for those systems with
 very low memory (<= 32Mb).
-It is recommended that if this
-needs to be increased above 1024, TCP_SYNQ_HSIZE in
+
+Prior to Linux 2.6.20,
+.\" commit 72a3effaf633bcae9034b7e176bdbd78d64a71db
+it was recommended that if this needed to be increased above 1024,
+the size of the SYNACK hash table (TCP_SYNQ_HSIZE) in
 .I include/net/tcp.h
 be modified to keep
 TCP_SYNQ_HSIZE*16<=tcp_max_syn_backlog, and the kernel be
-recompiled.
+recompiled. In Linux 2.6.20, the fixed sized TCP_SYNQ_HSIZE was removed
+in favour of dynamic sizing.
 .TP
 .IR tcp_max_tw_buckets " (integer; default: see below; since Linux 2.4)"
 .\" Since 2.3.41
-- 
1.9.1


Thank you for your time.

Regards,
Peter Adkins
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Re: [PATCH] tcp.7: Document removal of TCP_SYNQ_HSIZE

[Michael Kerrisk (man-pages)]

On 03/12/2015 08:15 AM, Peter Adkins wrote:
> Hello there,
> 
> Looking over the man page for 'tcp' I came across a reference to
> tuning the 'TCP_SYNQ_HSIZE' parameter when increasing
> 'tcp_max_syn_backlog' above 1024. However, this static sizing was
> removed back in Linux 2.6.20 in favour of dynamic scaling - as part of
> commit 72a3effaf633bcae9034b7e176bdbd78d64a71db.
> 
> I have included a patch below with reference to this commit, and that
> the process detailed is not required on >= Linux 2.6.20. This is my
> first patch for a man page, as well as groff, so I apologize if
> anything is incorrect. If so, please let me know and I will resolve
> and resubmit.
> 
> This patch was prepared against the current HEAD - at time of writing
> - from the Kernel.org man-page repository
> (f6d086878485f63e390d10f59b6beae7b96c4120), which looks to be version
> 3.82.

Thanks, Peter! Applied.

Cheers,

Michael


> ---
>  man7/tcp.7 | 10 +++++++---
>  1 file changed, 7 insertions(+), 3 deletions(-)
> 
> diff --git a/man7/tcp.7 b/man7/tcp.7
> index 5723bde..794c636 100644
> --- a/man7/tcp.7
> +++ b/man7/tcp.7
> @@ -530,12 +530,16 @@ The default value of 256 is increased to
>  1024 when the memory present in the system is adequate or
>  greater (>= 128Mb), and reduced to 128 for those systems with
>  very low memory (<= 32Mb).
> -It is recommended that if this
> -needs to be increased above 1024, TCP_SYNQ_HSIZE in
> +
> +Prior to Linux 2.6.20,
> +.\" commit 72a3effaf633bcae9034b7e176bdbd78d64a71db
> +it was recommended that if this needed to be increased above 1024,
> +the size of the SYNACK hash table (TCP_SYNQ_HSIZE) in
>  .I include/net/tcp.h
>  be modified to keep
>  TCP_SYNQ_HSIZE*16<=tcp_max_syn_backlog, and the kernel be
> -recompiled.
> +recompiled. In Linux 2.6.20, the fixed sized TCP_SYNQ_HSIZE was removed
> +in favour of dynamic sizing.
>  .TP
>  .IR tcp_max_tw_buckets " (integer; default: see below; since Linux 2.4)"
>  .\" Since 2.3.41
> 


-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
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