Date: Wed, 13 Sep 2017 11:24:26 -0600 From: Warner Losh <imp@bsdimp.com> To: Alan Somers <asomers@freebsd.org> Cc: "Michael W. Lucas" <mwlucas@michaelwlucas.com>, "freebsd-hackers@freebsd.org" <hackers@freebsd.org> Subject: Re: required kernel rebuilds Message-ID: <CANCZdfruXxGvYuk_Vg11maCgTOLdeGZbtyxwAXxKQB_KsC4NbA@mail.gmail.com> In-Reply-To: <CAOtMX2g6F9nb8xt-h=zWZHRsO9bFvyFaG-DXn9ki8NE49eQQhQ@mail.gmail.com> References: <20170913155542.GA25871@mail.michaelwlucas.com> <CAOtMX2g6F9nb8xt-h=zWZHRsO9bFvyFaG-DXn9ki8NE49eQQhQ@mail.gmail.com>
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On Wed, Sep 13, 2017 at 10:07 AM, Alan Somers <asomers@freebsd.org> wrote: > On Wed, Sep 13, 2017 at 9:55 AM, Michael W. Lucas > <mwlucas@michaelwlucas.com> wrote: > > Hi, > > > > Book research question. > > > > Way back in the Dark Ages of the 1990s, it wasn't uncommon to rebuild > > a kernel to fix a recurring panic. You'd have to tune MAXUSERS, or > > PMAP_SHPGPERPROC. > > > > AFAIK, dang near everything is tunable in either loader.conf or > > sysctl.conf. I really want to say that kernel rebuilds for these kinds > > of limits aren't needed any more. > > > > Does anyone have a counter-example, though? Is anything possibly > > crash-inducing non-tunable without a kernel rebuild? > > > > Thanks, > > ==ml > > Enabling VIMAGE still requires a kernel rebuild, because of the > possibility of crashes. I've seen such crashes on 10.2 or 10.3. I > don't know if they're fixed in 11.1, but I haven't seen any yet. > Changing MAXPHYS also requires a kernel rebuild. AFAIK MAXPHYS isn't > related to any kernel crashes, but it does have performance > implications. > MAXPHYS isn't currently dynamic. We have to set it at Netflix because we want to do super large I/Os. We'd just bump it in base, but it requires extra memory for every single I/O (since there's arrays in struct buf / bio based on this size for pages related to the I/O). I've had one kernel panic that was fixed by changing MAXPHYS, but that was due to a stupid driver bug... Warner
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