On 12/12/17 11:32, John Baldwin wrote:
On 12/11/17 5:26 AM, Eugene Grosbein wrote:
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.
I suspect two things are at play in running out of stack in 10.x and later.
1) Usage of XSAVE for AVX, etc. state uses more of the kstack (as kib@ alludes
to), and 2) clang. Certainly for MIPS I have found that compiling with clang
instead of gcc for mips64 gives a kernel that panics for stack overflow for any
use of NFS. It might be that this is due to something MIPS-specific, but it
might be worthwhile retesting with kstack_pages=2 and building the kernel
with CROSS_TOOLCHAIN=i386-gcc after installing the appropriate package.
For what it's worth, I see the same NFS-related stack overflows on
mips64 with in-tree GCC 4.2.1.
-Nathan
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