[Top][All Lists]
[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [Qemu-devel] Re: Strategic decision: COW format
From: |
Avi Kivity |
Subject: |
Re: [Qemu-devel] Re: Strategic decision: COW format |
Date: |
Wed, 23 Feb 2011 17:59:16 +0200 |
User-agent: |
Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.13) Gecko/20101209 Fedora/3.1.7-0.35.b3pre.fc14 Lightning/1.0b3pre Thunderbird/3.1.7 |
On 02/23/2011 05:47 PM, Anthony Liguori wrote:
I don't see how that works, since the memory image is duplicated for
each snapshot. So thousands of snapshots = terabytes of storage, and
hours of creating the snapshots.
Fabrice wanted to use CoW to as a mechanism to deduplicate the memory
contents with the on-disk state specifically to address this problem.
For the longest time, there was a comment in the savevm code along
these lines. It might still be there.
I think the lack of on-disk hashes was a critical missing bit to make
this feature really work well.
So you have to use dirty logging to see which pages changed, otherwise
you have to dedup all of them. Still I think migration/kemari is a
better fit for this.
Can you elaborate? What's the problem with a linear array of
snapshots (say up to 10,000 snapshots)?
Lots of things. The array will start to consume quite a bit of
contiguous space as it gets larger which means it needs to be relocated.
If you double the space each time, it amortizes out.
A snapshot seems to be around 40 bytes. So 10K snapshots = 400KB,
hardly a huge amount (sans pointed-to data which doesn't need to move).
Deleting a snapshot is a far more expensive operation than it needs to
be.
Move the last snapshot into the deleted entry?
--
error compiling committee.c: too many arguments to function
- Re: [Qemu-devel] Re: Strategic decision: COW format, (continued)
- Re: [Qemu-devel] Re: Strategic decision: COW format, Avi Kivity, 2011/02/23
- Re: [Qemu-devel] Re: Strategic decision: COW format, Anthony Liguori, 2011/02/23
- Re: [Qemu-devel] Re: Strategic decision: COW format, Kevin Wolf, 2011/02/23
- Re: [Qemu-devel] Re: Strategic decision: COW format, Anthony Liguori, 2011/02/23
- Re: [Qemu-devel] Re: Strategic decision: COW format, Avi Kivity, 2011/02/23
- Re: [Qemu-devel] Re: Strategic decision: COW format, Anthony Liguori, 2011/02/23
- Re: [Qemu-devel] Re: Strategic decision: COW format,
Avi Kivity <=
- Re: [Qemu-devel] Re: Strategic decision: COW format, Kevin Wolf, 2011/02/23
- Re: [Qemu-devel] Re: Strategic decision: COW format, Avi Kivity, 2011/02/23
- Re: [Qemu-devel] Re: Strategic decision: COW format, Anthony Liguori, 2011/02/23
- Re: [Qemu-devel] Re: Strategic decision: COW format, Avi Kivity, 2011/02/23
- Re: [Qemu-devel] Re: Strategic decision: COW format, Anthony Liguori, 2011/02/23
- Re: [Qemu-devel] Re: Strategic decision: COW format, Gleb Natapov, 2011/02/23
- Re: [Qemu-devel] Re: Strategic decision: COW format, Avi Kivity, 2011/02/23
- Re: [Qemu-devel] Re: Strategic decision: COW format, Anthony Liguori, 2011/02/23
- Re: [Qemu-devel] Re: Strategic decision: COW format, Avi Kivity, 2011/02/23
- Re: [Qemu-devel] Re: Strategic decision: COW format, Anthony Liguori, 2011/02/23