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Re: [Qemu-devel] [PATCH 2/3] qcow2: add option to clean unused cache ent

From: Max Reitz
Subject: Re: [Qemu-devel] [PATCH 2/3] qcow2: add option to clean unused cache entries after some time
Date: Thu, 28 May 2015 17:23:40 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0

On 28.05.2015 17:19, Alberto Garcia wrote:
On Thu 28 May 2015 05:14:12 PM CEST, Max Reitz wrote:
          'compat': 'str',
          '*lazy-refcounts': 'bool',
          '*corrupt': 'bool',
-      'refcount-bits': 'int'
+      'refcount-bits': 'int',
+      'cache-clean-interval': 'int'
      } }
I'm not too happy about making this part of ImageInfoSpecificQCow2.
Two reasons for this: First, it's eventually part of ImageInfo,
which is defined as "Information about a QEMU image file", but this
option cannot be set in the image file itself but is only a run-time

Can we mark the parameter optional, and only provide it when it is
non-zero?  That way, qemu-img (which cannot set an interval) will not
report it, and the only time it will appear is if it was set as part
of opening the block device under qemu.
That sounds good.
But what do we do with the other parameters (refcount-cache-size,
l2-cache-size)? We cannot have the same solution there because they
don't belong to the image file either, and they're never going go be

Pssht, don't mention it, or Eric will notice. :-)

Well, one solution would be to remember whether they have been set explicitly or not. But that gets ugly really quickly. Maybe Kevin's series helps there, but I don't know.

Of course, the simplest solution is to worry about cache-clean-interval for now and worry about the cache sizes later… But that basically means "We'll never worry about them unless someone complains", so…


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