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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:1.9.1.12) 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.
Regards, Anthony Liguori
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