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Date: Tue, 03 Nov 2009 02:23:08 -0800 From: ebiederm@...ssion.com (Eric W. Biederman) To: Eric Dumazet <eric.dumazet@...il.com> Cc: "David S. Miller" <davem@...emloft.net>, Greg KH <greg@...ah.com>, Benjamin LaHaise <bcrl@...et.ca>, Octavian Purdila <opurdila@...acom.com>, netdev@...r.kernel.org, Cosmin Ratiu <cratiu@...acom.com>, linux-kernel@...r.kernel.org Subject: Re: [PATCH] sysctl: reduce ram usage by 40 % Eric Dumazet <eric.dumazet@...il.com> writes: > Eric Dumazet a écrit : > >> Its curious because in my tests the biggest problems come from >> kernel/sysctl.c (__register_sysctl_paths) consuming 80% of cpu >> in following attempt to create 20.000 devices I bet that is Al's cute glue all the sysctl data structures together patch. It improves readdir and lookup at a small cost at registration time. >> (disable hotplug before trying this, and ipv6 too !) >> modprobe dummy numdummies=20000 >> I believe we should address __register_sysctl_paths() scalability >> problems too. Agreed. >> I dont know what is the 'sentinel' we allocate after each struct ctl_table >> But I suspect we could reduce size requirement of the 'sentinel' to include >> only needed fields for the sentinel (and move them at start of ctl_table) The sentinel is just a NULL terminator. > Here is the patch to reduce ram usage of sysctl : > > [PATCH] sysctl: reduce ram usage by 40 % > > We currently reserve space for a so called sentinel, a full struct ctl_table > for each ctl_table. We can cheat a bit since only needed fields of a sentinel > are ctl_name and procname. Add a new structure (struct ctl_table_sentinel) > that includes a full ctl_table and only required part of a sentinel. Before we address sysctl I would like to get out my patchset that makes sys_sysctl a wrapper around the ascii version of /proc/sys/net. Once that goes in it becomes much easier to do things and perform radical surgery on sysctl. Little things like .ctl_name and .strategy go away. Have you happened to look at the other cost of /proc proper? Hmm. Except for /proc/net/dev_snmp6 it doesn't look like we keep per interface directories in proc so without ivp6 you won't see the proc generic code at all. The practical consequence is if /proc/net/dev_snmp6 is not painful during registration right now we can probably convert all of /proc/sys/net to proc generic after my other changes are in. Eric -- 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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