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[Qemu-devel] Re: NBD server for QEMU images
From: |
Salvador Fandino |
Subject: |
[Qemu-devel] Re: NBD server for QEMU images |
Date: |
Wed, 13 Dec 2006 20:14:58 +0100 |
User-agent: |
Icedove 1.5.0.8 (X11/20061128) |
Avi Kivity wrote:
> Martin Guy wrote:
>>> - write tons of data to nbd device, data ends up in pagecache
>>> - memory gets low, kswapd wakes up, calls nbd device to actually write
>>> the data
>>> - nbd issues a request, which ends up on the nbd server on the same
>>> machine
>>> - the nbd server allocates memory
>>> - memory allocation hangs waiting for kswapd
>>
>> In other words, it can deadlock only if you are swapping to an nbd
>> device that is served by nbd-server running on the same machine and
>> kernel.
>
> No. It is possible if you issue non-O_SYNC writes.
I have run some tests and found that it's easy to cause a deadlock just
untaring a file over an nbd device being served from localhost (using
the standard nbd-server or my own, it doesn't matter).
Another interesting finding is that when the deadlock happens, qemu-nbds
is inside a read() call, waiting for new nbd requests to arrive over the
socket, and so, not trying to allocate memory or writing to disk.
BTW, I am using Debian unstable with kernel 2.6.18-1-686
Regards,
- Salva
- [Qemu-devel] Re: RE : Re: Re: NBD server for QEMU images, (continued)
- [Qemu-devel] Re: NBD server for QEMU images, Anthony Liguori, 2006/12/12
- [Qemu-devel] Re: NBD server for QEMU images, Salvador Fandino, 2006/12/12
- [Qemu-devel] Re: NBD server for QEMU images, Anthony Liguori, 2006/12/12
- Re: [Qemu-devel] Re: NBD server for QEMU images, Mark Williamson, 2006/12/12
- Re: [Qemu-devel] Re: NBD server for QEMU images, Avi Kivity, 2006/12/13
- Re: [Qemu-devel] Re: NBD server for QEMU images, Martin Guy, 2006/12/13
- Re: [Qemu-devel] Re: NBD server for QEMU images, Avi Kivity, 2006/12/13
- [Qemu-devel] Re: NBD server for QEMU images,
Salvador Fandino <=
- Re: [Qemu-devel] Re: NBD server for QEMU images, Avi Kivity, 2006/12/14
Re: [Qemu-devel] NBD server for QEMU images, Mulyadi Santosa, 2006/12/13