Date: Mon, 11 Dec 2017 17:26:12 +0700 From: Eugene Grosbein <eugen@grosbein.net> To: Konstantin Belousov <kostikbel@gmail.com>, Conrad Meyer <cem@FreeBSD.org> Cc: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: Re: svn commit: r326758 - in head/sys/i386: conf include Message-ID: <5A2E5D44.9030904@grosbein.net> In-Reply-To: <20171211091943.GF2272@kib.kiev.ua> References: <201712110432.vBB4WbnE021090@repo.freebsd.org> <20171211091943.GF2272@kib.kiev.ua>
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On 11.12.2017 16:19, Konstantin Belousov wrote: > On Mon, Dec 11, 2017 at 04:32:37AM +0000, Conrad Meyer wrote: >> Author: cem >> Date: Mon Dec 11 04:32:37 2017 >> New Revision: 326758 >> URL: https://svnweb.freebsd.org/changeset/base/326758 >> >> Log: >> i386: Bump KSTACK_PAGES default to match amd64 > i386 is not amd64, the change is wrong. > > i386 has the word size two times smaller than amd64, which makes typical > frame smaller by 30-40% over same code on amd64. Also i386 has much > smaller available KVA size (tens of MB) and KVA fragmentation is both > more severe and more fatal due to this. I expect that your change will > make any non-trivial load which creates enough threads to either fail > randomly or deadlock. > > If somebody tries to fit large load onto i386 machine, he must know what to > do and how to configure the kernel to adapt to the load (which does not > require the recompilation). Its very easy to get kernel stack overflow with 11-STABLE/i386 without any significant load due to abuse of kernel stack in many kernel subsystems as shown in the https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=219476 Contrary, "enough threads" seems to be very non-trivial number of threads and pretty unusual load pattern for i386 as I run several such systems with kern.kstack_pages=4 for quite long time and have no problems. No random fails, no deadlocks. And with 2 pages only 11-STABLE/i386 is just unusable if one utilizes SCTP, IPv6, some WiFi connectivity, IPSEC or even very small ZFS pool. I still wonder if there is really such load pattern that creates "enough threads" for i386 to make 4-pages stack troublesome. Eugene Grosbein
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