From: Takuya Yoshikawa <yoshikawa.takuya@oss•ntt.co.jp>
To: Marcelo Tosatti <mtosatti@redhat•com>
Cc: linux-arch@vger•kernel.org, arnd@arndb•de, kvm@vger•kernel.org,
kvm-ia64@vger•kernel.org, fernando@oss•ntt.co.jp, x86@kernel•org,
agraf@suse•de, kvm-ppc@vger•kernel.org,
linux-kernel@vger•kernel.org, linuxppc-dev@ozlabs•org,
mingo@redhat•com, paulus@samba•org, avi@redhat•com,
hpa@zytor•com, tglx@linutronix•de,
Takuya Yoshikawa <takuya.yoshikawa@gmail•com>
Subject: Re: [RFC][PATCH 11/12] KVM: introduce new API for getting/switching dirty bitmaps
Date: Wed, 12 May 2010 15:03:36 +0900 [thread overview]
Message-ID: <4BEA44B8.7050409@oss.ntt.co.jp> (raw)
In-Reply-To: <20100511140712.GA7063@amt.cnet>
>>> 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.
next prev parent reply other threads:[~2010-05-12 5:59 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-05-04 12:56 [RFC][PATCH 0/12] KVM, x86, ppc, asm-generic: moving dirty bitmaps to user space Takuya Yoshikawa
2010-05-04 12:58 ` [RFC][PATCH 1/12 applied today] KVM: x86: avoid unnecessary bitmap allocation when memslot is clean Takuya Yoshikawa
2010-05-04 13:00 ` [RFC][PATCH 2/12] KVM: introduce slot level dirty state management Takuya Yoshikawa
2010-05-04 13:01 ` [RFC][PATCH 3/12] KVM: introduce wrapper functions to create and destroy dirty bitmaps Takuya Yoshikawa
2010-05-04 13:02 ` [RFC][PATCH 4/12] x86: introduce copy_in_user() for 32-bit Takuya Yoshikawa
2010-05-04 13:02 ` [RFC][PATCH 5/12] x86: introduce __set_bit() like function for bitmaps in user space Takuya Yoshikawa
2010-05-04 13:03 ` [RFC][PATCH 6/12 not tested yet] PPC: introduce copy_in_user() for 32-bit Takuya Yoshikawa
2010-05-04 13:04 ` [RFC][PATCH 7/12 not tested yet] PPC: introduce __set_bit() like function for bitmaps in user space Takuya Yoshikawa
2010-05-11 16:00 ` Alexander Graf
2010-05-12 9:25 ` Takuya Yoshikawa
2010-05-04 13:05 ` [RFC][PATCH resend 8/12] asm-generic: bitops: introduce le bit offset macro Takuya Yoshikawa
2010-05-04 15:03 ` Arnd Bergmann
2010-05-04 16:08 ` Avi Kivity
2010-05-05 2:59 ` Takuya Yoshikawa
2010-05-06 13:38 ` Arnd Bergmann
2010-05-10 11:46 ` Takuya Yoshikawa
2010-05-10 12:01 ` Avi Kivity
2010-05-10 12:01 ` Arnd Bergmann
2010-05-10 12:09 ` Takuya Yoshikawa
2010-05-04 13:06 ` [RFC][PATCH 9/12] KVM: introduce a wrapper function of set_bit_user_non_atomic() Takuya Yoshikawa
2010-05-04 13:07 ` [RFC][PATCH RFC 10/12] KVM: move dirty bitmaps to user space Takuya Yoshikawa
2010-05-11 3:28 ` Marcelo Tosatti
2010-05-12 6:27 ` Takuya Yoshikawa
2010-05-04 13:08 ` [RFC][PATCH 11/12] KVM: introduce new API for getting/switching dirty bitmaps 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 6:03 ` Takuya Yoshikawa [this message]
2010-05-04 13:11 ` [RFC][PATCH 12/12 sample] qemu-kvm: use " Takuya Yoshikawa
2010-05-10 12:06 ` [RFC][PATCH 0/12] KVM, x86, ppc, asm-generic: moving dirty bitmaps to user space Avi Kivity
2010-05-10 12:26 ` Takuya Yoshikawa
2010-05-11 10:11 ` Takuya Yoshikawa
2010-05-13 11:47 ` Avi Kivity
2010-05-17 9:06 ` Takuya Yoshikawa
2010-05-11 15:55 ` Alexander Graf
2010-05-12 9:19 ` Takuya Yoshikawa
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