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Re: [PATCH v10 7/7] multifd: Implement zero copy write in multifd migrat
From: |
Daniel P . Berrangé |
Subject: |
Re: [PATCH v10 7/7] multifd: Implement zero copy write in multifd migration (multifd-zero-copy) |
Date: |
Wed, 27 Apr 2022 09:46:31 +0100 |
User-agent: |
Mutt/2.1.5 (2021-12-30) |
On Tue, Apr 26, 2022 at 08:06:56PM -0300, Leonardo Bras wrote:
> Implement zero copy send on nocomp_send_write(), by making use of QIOChannel
> writev + flags & flush interface.
>
> Change multifd_send_sync_main() so flush_zero_copy() can be called
> after each iteration in order to make sure all dirty pages are sent before
> a new iteration is started. It will also flush at the beginning and at the
> end of migration.
>
> Also make it return -1 if flush_zero_copy() fails, in order to cancel
> the migration process, and avoid resuming the guest in the target host
> without receiving all current RAM.
>
> This will work fine on RAM migration because the RAM pages are not usually
> freed,
> and there is no problem on changing the pages content between
> writev_zero_copy() and
> the actual sending of the buffer, because this change will dirty the page and
> cause it to be re-sent on a next iteration anyway.
>
> A lot of locked memory may be needed in order to use multifd migration
> with zero-copy enabled, so disabling the feature should be necessary for
> low-privileged users trying to perform multifd migrations.
>
> Signed-off-by: Leonardo Bras <leobras@redhat.com>
> ---
> migration/multifd.h | 2 ++
> migration/migration.c | 11 ++++++++++-
> migration/multifd.c | 37 +++++++++++++++++++++++++++++++++++--
> migration/socket.c | 5 +++--
> 4 files changed, 50 insertions(+), 5 deletions(-)
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
With regards,
Daniel
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- [PATCH v10 5/7] multifd: multifd_send_sync_main now returns negative on error, (continued)