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Re: [Qemu-devel] Re: [PATCH v2 6/7] qed: Read/write support

From: Anthony Liguori
Subject: Re: [Qemu-devel] Re: [PATCH v2 6/7] qed: Read/write support
Date: Wed, 13 Oct 2010 09:53:30 -0500
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv: Gecko/20100915 Lightning/1.0b1 Thunderbird/3.0.8

On 10/13/2010 09:16 AM, Avi Kivity wrote:
 On 10/13/2010 04:11 PM, Anthony Liguori wrote:
Why would you ever update the header, apart from relocating L1 for some reason?

To update the L1/L2 tables clean bit. That's what prevents a check in the normal case where you have a clean shutdown.

I see - so you wouldn't update it every allocation, only when the disk has been quiet for a while.

Right, the current plan is to flush the header dirty bit on shutdown or whenever there is an explicit flush of the device. Current that is caused by either a guest-initiated flush or a L1 update. We also plan to add a timer-based flush such that a flush is scheduled for some period of time (like 5 minutes) after the dirty bit is set.

The end result should be that the only window for requiring a metadata scan is if a crash occurs within 5 minutes of a cluster allocation and an explicit flush has not occurred for some other reason.


Anthony Liguori

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