Date: Thu, 08 Nov 2012 11:11:25 +0100 From: Andre Oppermann <andre@freebsd.org> To: Peter Wemm <peter@wemm.org> Cc: Alfred Perlstein <alfred@freebsd.org>, John Baldwin <jhb@freebsd.org>, svn-src-all@freebsd.org, Alfred Perlstein <bright@mu.org>, svn-src-head@freebsd.org, src-committers@freebsd.org, Konstantin Belousov <kostikbel@gmail.com> Subject: Re: svn commit: r242029 - head/sys/kern Message-ID: <509B854D.9020301@freebsd.org> In-Reply-To: <CAGE5yCobr4ZU0DEWZSez1kp4jo_V4gSby0kGqFF06Dev_Cc_jA@mail.gmail.com> References: <201210250146.q9P1kLi8043704@svn.freebsd.org> <20121025080551.GG35915@deviant.kiev.zoral.com.ua> <201210250950.57161.jhb@freebsd.org> <509B501F.5050109@mu.org> <CAGE5yCobr4ZU0DEWZSez1kp4jo_V4gSby0kGqFF06Dev_Cc_jA@mail.gmail.com>
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On 08.11.2012 08:46, Peter Wemm wrote: > On Wed, Nov 7, 2012 at 10:24 PM, Alfred Perlstein <bright@mu.org> wrote: >> [[ + peter ]] >> >> Folks, I spent quite a bit of time trying to figure out how to resolve >> maxusers scaling in a happy way for all. >> >> I think I came up with a solution. >> >> This solution should work for i386, and other 32 bit platforms, as well as >> scaling well for 64 bit (or higher) platforms that have virtually unlimited >> AND 64bit with limited kernel address space. >> >> Here is how it works: >> >> We calculate the maxusers value based on physical memory, and then clamp it >> down if physical memory exceeds kernel addressable memory. >> >> The algorithm actually remains the same for all architectures, with the >> exception that machines with large kernel address space it is no longer >> clamped at 384. >> >> I've attached a test program that lets you play with various values for >> VM_MIN_KERNEL_ADDRESS, VM_MAX_KERNEL_ADDRESS and physpages. (argv[1, 2, 3] >> respectively.) >> >> Please give me your feedback. > > This is still bogus. VM_MIN_KERNEL_ADDRESS and VM_MAX_KERNEL_ADDRESS > have no bearing on how much space should be allocated for mbuf > clusters on amd64. If anything, you want dmapbase / dmapend if you > want a practical cap for amd64. Even then, jumbo clusters are >4K so > they come out of kva rather than direct map. > > maxusers is the wrong thing for this. maxusers should, if anything, > be used to set things like kern.maxproc. Preferably it should be > deleted entirely and sysctl.conf should be used to change > kern.maxproc. > > Setting limits for the mbuf / cluster pool should be a MD parameter. > > Trying to scale maxusers based on physical ram in order to get mbuf > cluster limits set as a side effect is just plain wrong. > > It makes no more sense than trying to set nmbclusters based on > PRINTF_BUFR_SIZE, and then trying to scale PRINTF_BUFR_SIZE in order > to get desirable second and third order side effects. > > Scale nmbclusters based on physical ram, with a MD method for capping > it for when there are MD limits (eg: disproportionately small kva on > an i386 PAE machine). Don't use maxusers. ACK -- Andre
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