[Top][All Lists]

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Qemu-devel] post-copy is broken?

From: Dr. David Alan Gilbert
Subject: Re: [Qemu-devel] post-copy is broken?
Date: Thu, 14 Apr 2016 13:34:41 +0100
User-agent: Mutt/1.5.24 (2015-08-30)

* Andrea Arcangeli (address@hidden) wrote:

> The next suspect is the massive THP refcounting change that went
> upstream recently:

> As further debug hint, can you try to disable THP and see if that
> makes the problem go away?

Yep, this seems to be the problem (cc'ing in Kirill).

122afea9626ab3f717b250a8dd3d5ebf57cdb56c - works (just before Kirill disables 
61f5d698cc97600e813ca5cf8e449b1ea1c11492 - breaks (when THP is reenabled)

It's pretty reliable; as you say disabling THP makes it work again
and putting it back to THP/madvise mode makes it break.  And you need
to test on a machine with some free ram to make sure THP has a chance
to have happened.

I'm not sure of all of the rework that happened in that series,
but my reading of it is that splitting of THP pages gets deferred;
so I wonder if when I do the madvise to turn THP off, if it's actually
still got THP pages and thus we end up with a whole THP mapped
when I'm expecting to be userfaulting those pages.


> Thanks,
> Andrea
Dr. David Alan Gilbert / address@hidden / Manchester, UK

reply via email to

[Prev in Thread] Current Thread [Next in Thread]