Re: suspending a domain in the ngio world

[Kip Macy <kmacy@fsmware.com>]

The dd is running in DOM1. The OOM killer is getting run in DOM0.
There is clearly a memory leak in the block I/O path.

DOM0 is curly and DOM1 is xen-vm0.

A large amount of memory has already been leaked:

kmacy@curly cat /proc/meminfo
        total:    used:    free:  shared: buffers:  cached:
Mem:  262565888 205619200 56946688        0 23339008 28123136
==
[root@xen-vm0 ~]$ dd if=/dev/zero of=/tmp/bwout bs=1024k count=256
==
kmacy@curly cat /proc/meminfo
        total:    used:    free:  shared: buffers:  cached:
Mem:  262565888 214687744 47878144        0 23339008 28123136
==
[root@xen-vm0 ~]$ dd if=/dev/zero of=/tmp/bwout count=256 bs=1024k
256+0 records in
256+0 records out
==
kmacy@curly cat /proc/meminfo | head -3
        total:    used:    free:  shared: buffers:  cached:
Mem:  262565888 223727616 38838272        0 23339008 28123136
==
[root@xen-vm0 ~]$ dd if=/dev/zero of=/tmp/bwout count=256 bs=1024k
256+0 records in
256+0 records out
==
kmacy@curly cat /proc/meminfo | head -2
        total:    used:    free:  shared: buffers:  cached:
Mem:  262565888 232873984 29691904        0 23339008 28123136

So ~40MB is leaked for every 1GB transferred.

I can give you a stack backtrace of the memory allocation failure in
DOM0 if you like, but as far as I can tell the horse has long since left
the barn at that point.

> This is within DOM1 (i.e., not DOM0) right? If so, I guess that doing
> this 'dd' test within DOM0 doesn't get you similar messages?
>
> This is rather unexpected -- if you could add a stack backtrace to the
> out-of-memory path in the page allocator (page_alloc.c in Xenolinux)
> an d post me that with the kernel image (vmlinux) then I'll see what I
> can work out. I guess I haven't tested all that hard so there might be
> a memory leak.

On a side note - I don't need suspend/restore, I just need coredump and
almost immediately after that PTRACE_STOP. So long as I can stop the
domain long enough to write out its state I have what I need.



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