From: Takuya Yoshikawa <yoshikawa.takuya@oss.ntt.co.jp>
To: kvm-ia64@vger.kernel.org
Subject: Re: [RFC][PATCH 11/12] KVM: introduce new API for getting/switching
Date: Wed, 12 May 2010 05:59:58 +0000 [thread overview]
Message-ID: <4BEA44B8.7050409@oss.ntt.co.jp> (raw)
In-Reply-To: <20100504220821.d68bde57.takuya.yoshikawa@gmail.com>
>>> One alternative would be:
>>>
>>> KVM_SWITCH_DIRTY_LOG passing the address of a bitmap. If the active
>>> bitmap was clean, it returns 0, no switch performed. If the active
>>> bitmap was dirty, the kernel switches to the new bitmap and returns 1.
>>>
>>> And the responsability of cleaning the new bitmap could also be left
>>> for userspace.
>>>
>>
>> That is a beautiful approach but we can do that only when we give up using
>> GET api.
>>
>>
>> I follow you and Avi's advice about that kind of maintenance policy!
>> What do you think?
>
> If you introduce a switch ioctl that frees the bitmap vmalloc'ed by the
> current set_memory_region (if its not freed already), after pointing the
> memslot to the user supplied one, it should be fine?
>
You mean switching from vmalloc'ed(not do_mmap'ed) one to user supplied one?
It may be possible but makes things really complicated in my view:
until some point we use set_bit, and then use set_bit_user, etc.
IMO:
- # of slots is limited and the size of dirty_bitmap_old pointer is not problematic.
- Both user side and kernel side need not allocate buffers every time and once
paired buffers are registered, we will reuse the buffers until user side orders
to stop logging.
- We have a tiny advantage if we need not copy_from_user to get a bitmap address
for switch ioctl.
=> So I think having two __user bitmaps is not a bad thing.
prev parent reply other threads:[~2010-05-12 5:59 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-05-04 13:08 [RFC][PATCH 11/12] KVM: introduce new API for getting/switching Takuya Yoshikawa
2010-05-11 3:43 ` Marcelo Tosatti
2010-05-11 5:53 ` Takuya Yoshikawa
2010-05-11 14:07 ` Marcelo Tosatti
2010-05-12 5:59 ` Takuya Yoshikawa [this message]
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