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Re: [Qemu-devel] [RFC] block-trace Low Level Command Supporting Disk Int
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] [RFC] block-trace Low Level Command Supporting Disk Introspection |
Date: |
Wed, 15 May 2013 05:16:15 -0400 (EDT) |
> > We don't need a way to pass data from before to after hooks, a simple
> > scan of a linked list will do.
>
> So in this case the linked list is the way.
Point taken. :)
> > > Does the "if there was no room" part mean that the mirror is active only
> > > sometimes?
> >
> > Yes, otherwise the guest can allocate arbitrary amounts of memory in the
> > host just by starting a few very large I/O operations.
>
> I think I would rather throttle I/O in this case, i.e. requests wait
> until they can get the space. At least for a synchronous mirror we
> have to do something like this.
Yes, but this is still asynchronous. The active part is just an optimization
to avoid write amplification (where small random writes require I/O of an entire
block as big as the bitmap granularity).
> > > And why even bother with a dirty bitmap for an active mirror? The
> > > background job that sequentially processes the whole image only needs a
> > > counter, no bitmap.
> >
> > That's not enough for the case when the host crashes and you have to
> > restart the mirroring or complete it offline.
>
> You're thinking of a persistent bitmap here? Makes sense then, I didn't
> think about that.
Yes.
Paolo
- Re: [Qemu-devel] [RFC] block-trace Low Level Command Supporting Disk Introspection, (continued)
- Re: [Qemu-devel] [RFC] block-trace Low Level Command Supporting Disk Introspection, Stefan Hajnoczi, 2013/05/14
- Re: [Qemu-devel] [RFC] block-trace Low Level Command Supporting Disk Introspection, Kevin Wolf, 2013/05/14
- Re: [Qemu-devel] [RFC] block-trace Low Level Command Supporting Disk Introspection, Paolo Bonzini, 2013/05/14
- Re: [Qemu-devel] [RFC] block-trace Low Level Command Supporting Disk Introspection, Wolfgang Richter, 2013/05/14
- Re: [Qemu-devel] [RFC] block-trace Low Level Command Supporting Disk Introspection, Paolo Bonzini, 2013/05/14
- Re: [Qemu-devel] [RFC] block-trace Low Level Command Supporting Disk Introspection, Wolfgang Richter, 2013/05/14
- Re: [Qemu-devel] [RFC] block-trace Low Level Command Supporting Disk Introspection, Kevin Wolf, 2013/05/15
- Re: [Qemu-devel] [RFC] block-trace Low Level Command Supporting Disk Introspection, Paolo Bonzini, 2013/05/15
- Re: [Qemu-devel] [RFC] block-trace Low Level Command Supporting Disk Introspection, Kevin Wolf, 2013/05/15
- Re: [Qemu-devel] [RFC] block-trace Low Level Command Supporting Disk Introspection,
Paolo Bonzini <=
- Re: [Qemu-devel] [RFC] block-trace Low Level Command Supporting Disk Introspection, Kevin Wolf, 2013/05/15
- Re: [Qemu-devel] [RFC] block-trace Low Level Command Supporting Disk Introspection, Paolo Bonzini, 2013/05/15
- Re: [Qemu-devel] [RFC] block-trace Low Level Command Supporting Disk Introspection, Wolfgang Richter, 2013/05/22
Re: [Qemu-devel] [RFC] block-trace Low Level Command Supporting Disk Introspection, Wolfgang Richter, 2013/05/14
Re: [Qemu-devel] [RFC] block-trace Low Level Command Supporting Disk Introspection, Richard W.M. Jones, 2013/05/16