Messages in this thread | | | Date | Sat, 19 Apr 2008 22:29:16 -0500 | From | Eric Sandeen <> | Subject | Re: x86: 4kstacks default |
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Ingo Molnar wrote: > * Andrew Morton <akpm@linux-foundation.org> wrote: > >>> config 4KSTACKS >>> bool "Use 4Kb for kernel stacks instead of 8Kb" >>> - depends on DEBUG_KERNEL >>> depends on X86_32 >>> + default y >> This patch will cause kernels to crash. > > what mainline kernels crash and how will they crash? Fedora and other > distros have had 4K stacks enabled for years: > > $ grep 4K /boot/config-2.6.24-9.fc9 > CONFIG_4KSTACKS=y > > and we've conducted tens of thousands of bootup tests with all sorts of > drivers and kernel options enabled and have yet to see a single crash > due to 4K stacks.
Really, not one?
https://bugzilla.redhat.com/show_bug.cgi?id=247158 https://bugzilla.redhat.com/show_bug.cgi?id=227331 https://bugzilla.redhat.com/show_bug.cgi?id=240077
(hehe, ok, xfs is a common component there...)
and it's not always obvious that you've overflowed the stack.
CONFIG_DEBUG_STACKOVERFLOW isn't ery useful because the warning printk it generates uses the remaining amount of stack, and tips the box.
> So basically the kernel default just follows the > common distro default now. (distros and users can still disable it)
If Fedora is the common distro, ok. :)
Fedora is a pretty narrow sample in terms of IO stacks at least. I have plenty of fondness for Fedora, but it's almost 100% ext3[1]. I spent a fair amount of time getting xfs+lvm to survive 4k on F8; gcc caused stack usage to grow in general from F7 to F8, and F9 seems to have gotten tight again but I haven't gotten to the bottom of yet.
Heck my ext3-root-on-sda1 pre-beta F9 box, no nfs or lvm or xfs or anything gets within 744 bytes of the end of the 4k stack simply by *booting* (it was a modprobe process... maybe some module needs help)
How many other distros use 4K stacks on x86, really?
-Eric
[1] http://www.smolts.org/static/stats/stats.html shows 24588 ext3 filesystems, compared to 366 xfs, 248 reiserfs, 76 jfs ...
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