Qian Cai <[email protected]> writes:
> On Tue, Jun 09, 2020 at 10:50:50PM +0200, Thomas Gleixner wrote:
>> Thomas Gleixner <[email protected]> writes:
>> >> BAD (after oom02)
>> >> # cat /sys/kernel/debug/stackdepot/info
>> >> Unique stacks: 140476
>> >
>> > That's indeed odd. I try to reproduce and figure out what really breaks
>> > here.
>>
>> I checked your config file and I think I know where this comes from. Can
>> you plase disable KASAN just for testing purposes and compare before
>> after again?
>
> It turns out I'll need a few days to be able to get ahold of those
> affected systems again. I'll be reporting back as soon as possible.
I figured it out. It has nothing to do with asm_call_on...(). It's also
unrelated to page_owner. It's purely a KASAN issue.
KASAN trims stack traces with the help of filter_irq_stacks() which
relies on __irqentry_text_start/end
The entry rework moved the interrupt entry points out of the irqentry
section, which breaks that filter function.
I made it work again. Here are the numbers which make that obvious:
Mainline:
Unique stacks: 23403
Depot index: 244
Depot offset: 4208
x86/entry:
Unique stacks: 38835
Depot index: 464
Depot offset: 7616
x86/entry + fix:
Unique stacks: 23607
Depot index: 247
Depot offset: 14224
So with the non-working trimming this generates more unique stacks and
because they are not trimmed they become larger and eat more storage
space. The resulting average per stack shows that:
Mainline: 171 bytes per stack
x86/entry: 195 bytes per stack
x86/entry + fix: 172 bytes per stack
I'll point you to a test branch shortly.
Thanks,
tglx
