Date: Fri, 09 Nov 2012 18:56:30 -0800 From: Alfred Perlstein <bright@mu.org> To: Eitan Adler <eadler@freebsd.org> Cc: svn-src-head@freebsd.org, svn-src-all@freebsd.org, Alfred Perlstein <alfred@freebsd.org>, src-committers@freebsd.org Subject: Re: svn commit: r242847 - in head/sys: i386/include kern Message-ID: <509DC25E.5030306@mu.org> In-Reply-To: <CAF6rxg=HPmQS1T-LFsZ=DuKEqH30iJFpkz%2BJGhLr4OBL8nohjg@mail.gmail.com> References: <201211100208.qAA28e0v004842@svn.freebsd.org> <CAF6rxg=HPmQS1T-LFsZ=DuKEqH30iJFpkz%2BJGhLr4OBL8nohjg@mail.gmail.com>
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On 11/9/12 6:34 PM, Eitan Adler wrote: > On 9 November 2012 21:08, Alfred Perlstein <alfred@freebsd.org> wrote: >> Modified: head/sys/kern/subr_param.c >> +#ifdef VM_MAX_AUTOTUNE_MAXUSERS >> + if (maxusers > VM_MAX_AUTOTUNE_MAXUSERS) >> + maxusers = VM_MAX_AUTOTUNE_MAXUSERS; >> +#endif >> + /* >> + * Scales down the function in which maxusers grows once >> + * we hit 384. >> + */ >> + if (maxusers > 384) >> + maxusers = 384 + ((maxusers - 384) / 8); >> + } > Hey, > > I know you didn't introduce this magic number 384. But can you (or > someone else) explain where it came from? > Sure, this is magic for i386 PAE machines. 384 maxusers was pretty much the highest you wanted auto-tuned SAFELY for 32bit KVA on i386. Now with 64 bit machines doing away with this hard ceiling, I wanted to change the slope so that it doesn't grow too much as a conservative measure to test the waters. Take for example my amd64 machine with 16GB of ram. Without the scaling factor of "maxusers = 384 + ((maxusers - 384) / 8)" then I get 8173 maxusers. 8173 maxusers translates to 524096 nmbclusters (1024 + 8173 * 64). That is 2GB RAM for just nmbclusters, nevermind jumbo9 and jumbo16. With the scaling adjustment I get 1357 maxusers which is 87872 nmbclusters. That is 343MB. Somewhat more reasonable. I'm open to other suggestions and people coming in here to open the value up higher... however I wanted a conservative value for now to avoid too much concern. We'll see where this takes us. -Alfred With this patch I get 75104 nmbclusters, which is 75104 pages which is 293 MB of ram!
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