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Date: Wed, 9 Jul 2008 18:28:02 -0400 From: "J. Bruce Fields" <bfields@...ldses.org> To: Evgeniy Polyakov <johnpol@....mipt.ru> Cc: Bill Fink <billfink@...dspring.com>, Stephen Hemminger <stephen.hemminger@...tta.com>, Roland Dreier <rdreier@...co.com>, David Miller <davem@...emloft.net>, aglo@...i.umich.edu, shemminger@...tta.com, netdev@...r.kernel.org, rees@...ch.edu Subject: Re: setsockopt() On Wed, Jul 09, 2008 at 10:43:30PM +0400, Evgeniy Polyakov wrote: > On Wed, Jul 09, 2008 at 02:11:22PM -0400, J. Bruce Fields (bfields@...ldses.org) wrote: > > > Yeah, its a bit confusing. It probably was copypasted, there is no > > > default, but minimum possible value. > > > > I don't understand; what do you mean by "there is no default"? (And if > > not, what does tcp_wmem[1] mean?) > > I meant there is no default value for tcp_w/rmem[2], which is calculated > based on tcp_mem, which in turn is calculated based on amount RAM of in > the system. tcp_wmem[2] will be at least 64k, but its higher limit > (calculated by system, which of course can be overwritten) is RAM/256 on > x86 (iirc only low mem is counted, although that was different in > various kernel versions), but not more than 4Mb. > > tcp_wmem[1] means initial send buffer size, it can grow up to tcp_wmem[2]. > There is a default for this parameter. Actually all this numbers are a > bit fluffy, so they are kind of soft rules for socket memory accounting > mechanics. OK, thanks. Would the following be any more clearer and/or accurate? --b. diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt index 17a6e46..a22af04 100644 --- a/Documentation/networking/ip-sysctl.txt +++ b/Documentation/networking/ip-sysctl.txt @@ -336,7 +336,7 @@ tcp_rmem - vector of 3 INTEGERs: min, default, max pressure. Default: 8K - default: default size of receive buffer used by TCP sockets. + default: initial size of receive buffer used by TCP sockets. This value overrides net.core.rmem_default used by other protocols. Default: 87380 bytes. This value results in window of 65535 with default setting of tcp_adv_win_scale and tcp_app_win:0 and a bit @@ -344,8 +344,10 @@ tcp_rmem - vector of 3 INTEGERs: min, default, max max: maximal size of receive buffer allowed for automatically selected receiver buffers for TCP socket. This value does not override - net.core.rmem_max, "static" selection via SO_RCVBUF does not use this. - Default: 87380*2 bytes. + net.core.rmem_max. Calling setsockopt() with SO_RCVBUF disables + automatic tuning of that socket's receive buffer size, in which + case this value is ignored. + Default: between 87380B and 4MB, depending on RAM size. tcp_sack - BOOLEAN Enable select acknowledgments (SACKS). @@ -419,19 +421,21 @@ tcp_window_scaling - BOOLEAN Enable window scaling as defined in RFC1323. tcp_wmem - vector of 3 INTEGERs: min, default, max - min: Amount of memory reserved for send buffers for TCP socket. + min: Amount of memory reserved for send buffers for TCP sockets. Each TCP socket has rights to use it due to fact of its birth. Default: 4K - default: Amount of memory allowed for send buffers for TCP socket - by default. This value overrides net.core.wmem_default used - by other protocols, it is usually lower than net.core.wmem_default. + default: initial size of send buffer used by TCP sockets. This + value overrides net.core.wmem_default used by other protocols. + It is usually lower than net.core.wmem_default. Default: 16K - max: Maximal amount of memory allowed for automatically selected - send buffers for TCP socket. This value does not override - net.core.wmem_max, "static" selection via SO_SNDBUF does not use this. - Default: 128K + max: Maximal amount of memory allowed for automatically tuned + send buffers for TCP sockets. This value does not override + net.core.wmem_max. Calling setsockopt() with SO_SNDBUF disables + automatic tuning of that socket's send buffer size, in which case + this value is ignored. + Default: between 64K and 4MB, depending on RAM size. tcp_workaround_signed_windows - BOOLEAN If set, assume no receipt of a window scaling option means the -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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