Date: Fri, 19 Aug 2016 12:35:30 +0300 From: Toomas Soome <tsoome@me.com> To: Konstantin Belousov <kostikbel@gmail.com> Cc: Warner Losh <imp@bsdimp.com>, Julian Elischer <julian@freebsd.org>, John Baldwin <jhb@freebsd.org>, src-committers <src-committers@freebsd.org>, "svn-src-all@freebsd.org" <svn-src-all@freebsd.org>, "svn-src-head@freebsd.org" <svn-src-head@freebsd.org> Subject: Re: svn commit: r304187 - in head: . share/man/man4 sys/conf sys/dev/mcd sys/modules sys/modules/mcd Message-ID: <514987E4-B953-467C-B53B-824B172A5211@me.com> In-Reply-To: <20160819092424.GE83214@kib.kiev.ua> References: <201608152038.u7FKc2NL026330@repo.freebsd.org> <2065331.KaGOSftJhd@ralph.baldwin.cx> <0d6c2e45-e4da-9bb7-a50c-212135d9ac4f@freebsd.org> <CANCZdfpY9S8ErwD6b7pHeH%2BRVF9JEszBb7zJ9m-wybfBr1ujAg@mail.gmail.com> <20160819073955.GC83214@kib.kiev.ua> <50AAF049-C8A7-4C69-A206-C3983FFA7867@me.com> <20160819092424.GE83214@kib.kiev.ua>
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> On 19. aug 2016, at 12:24, Konstantin Belousov <kostikbel@gmail.com> = wrote: >=20 > On Fri, Aug 19, 2016 at 11:50:35AM +0300, Toomas Soome wrote: >>=20 >>> On 19. aug 2016, at 10:39, Konstantin Belousov <kostikbel@gmail.com> = wrote: >>>=20 >>> On Thu, Aug 18, 2016 at 09:28:57PM -0600, Warner Losh wrote: >>>> On Thu, Aug 18, 2016 at 12:50 AM, Julian Elischer = <julian@freebsd.org> wrote: >>>>> On 16/08/2016 4:54 AM, John Baldwin wrote: >>>>>>=20 >>>>>> On Monday, August 15, 2016 08:38:02 PM John Baldwin wrote: >>>>>>>=20 >>>>>>> Author: jhb >>>>>>> Date: Mon Aug 15 20:38:02 2016 >>>>>>> New Revision: 304187 >>>>>>> URL: https://svnweb.freebsd.org/changeset/base/304187 >>>>>>>=20 >>>>>>> Log: >>>>>>> Remove the mcd(4) driver for Mitsumi CD-ROM players. >>>>>>> This is a driver for a pre-ATAPI ISA CD-ROM adapter. As = noted in >>>>>>> the manpage, this driver is only useful as a backend to = cdcontrol to >>>>>>> play audio CDs since it doesn't use DMA, so its data performance = is >>>>>>> "abysmal" (and that was true in the mid 90's). >>>>>>=20 >>>>>> No one stepped up to test patches for it either when I last = posted patches >>>>>> to >>>>>> convert it from timeout(9) to callout(9). I have a few more = drivers that >>>>>> are >>>>>> both very old and that people have no business using in 12 (think = ISA >>>>>> adapters that don't do DMA and can't be used with pccard) that I = will be >>>>>> removing over the next little while. I brought up a list of = drivers on >>>>>> arch@ >>>>>> a couple of years ago and the conversation drifted off into the = weeds >>>>>> about >>>>>> trimming GENERIC, etc. No one objected to the specific drivers I = listed >>>>>> though (and I got a few pleas of "please remove"). If someone = shows up >>>>>> desperately clutching an ISA adapter they can always dig up the = source >>>>>> from >>>>>> svn and deal with forward porting it for whatever API changes = have >>>>>> happened >>>>>> since it was removed. >>>>>=20 >>>>>=20 >>>>> I would imagine any machine still holding one of these probably = has not >>>>> enough memory to run FreeBSD. >>>>>=20 >>>>> would we still run in 2MB? >>>>=20 >>>> With insane levels of tuning, we can run in 32MB userland that can = do >>>> things. Even 64MB is tight w/o some tuning. 16MB is almost = certainly >>>> right out except for very specialized situations. 2MB? We can't = even >>>> load the loader in that :(. Oh, and all these memory configs are = only >>>> possible if you tweak the loader's block cache... >>>>=20 >>>=20 >>> 32MB is quite usable. Without any tuning, you get slightly less = than 10MB >>> for userspace, which is enough to for many things, and plenty if = swap is >>> added. >>>=20 >>> Note that you cannot boot on such configurations since loader was = broken, >>> but if you do manage to jump to kernel, things were fine several = months >>> ago. I tested my relatively recent OOM changes on 32MB qemu config. >>>> Warner >>>=20 >>=20 >> If the target is to go as low memory as possible, sure, you can strip = all off, from boot loader point, you should load kernel from stage2 and = not use loader at all (you can load and jump kernel even now from = stage2, assuming it wont need any special configuration from loader = config) etc etc. This means highly specialized build and has nothing to = do with generic all purpose system. >>=20 > Why you describe this as an 'alternative' ? Before that loader = changes, > I regularly tested on 32MB qemy i386 image and 64MB amd64 image. I do > not see anything extreme in these configs. They use normal boot path, > which provides kernels with debugging symbols, metadata, loaded = modules > etc. Why should I use deficient boot2-only loading, which, = additionally, > cannot work on amd64 ? >=20 > More, this is the only reasonable way for most developers to ensure = that > system is still usable on tiny configs found on embedded devices. = Right > now the min which I have to set up is 128MB, and VM changes are simply = not > tested on anything smaller. It is guaranteed that small systems will = grow > regressions fast. And I will not jump through the hoops to mitigate > breakage induced by other people' changes. >=20 >> Also at some point, there is an question about how reasonable it is = to have such configuration as part of generic code base for special bits = like boot loader itself, as the problem is, testing all those variants = is becoming impossible and even keeping reasonable code base in all of = the #if #else #endif spaghetti is getting quite hard and error prone. >>=20 >>> =46rom developers point of view, it is not really encouraging to = have possible feedback like ???oh, but you did break my 32MB system = boot??? ;) This does bring back some memories however. For first 2 unix = systems I was dealing with, one had 8MB and another had 12MB of = memory??? it was ~ 1992-1993;) >>=20 > Not mine, but you (?) indirectly broke system for people who do use = 32MB > on other arches, since low memory config on dev systems become 128MB. > I cared about 32MB before, but not any longer. Yep, I did set it to 64MB. And this is exactly why I wrote that small = systems do need special approaches, because getting updates for new = features and keeping tiny systems functional are conflicting options. So = far freebsd boot loader has managed this in some extent by massive = amount of preprocessor conditions and the result is insane list of = different boot programs in /boot - this is the price to pay. Even to = install the boot program you need to know when to use gpart and when = dd=E2=80=A6 rgds, toomas >=20 >> Right now the loader and stage2 are set to use 64MB heap to make it = possible to implement zfs feature support and later on, for more = features. >>=20 >> Also note that UEFI setups are much harder to deal with regard of = memory management, because as long as BS are in control, you can not = really control the memory management there and can end up with = fragmented unusable (for kernel loading) layout. This is especially = nasty as apparently some (buggy) systems actually have runtime services = using boot services memory areas, so you can end up in setup where you = can not re-use BS memory and those chunks can be all over the low memory = address space???=20 >=20 > Yes, I do suspect that eventually systems appear where our default > layout of the kernel physical segments is not workable and both loader > and kernel bootstrap would need to grow much more flexibility. Initial > 1GB-idmap page table structure and kernel page table would need to = handle > this, and we will need a kernel relocator either in loader or in = kernel > itself.
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