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From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
To: Peter Xu <peterx@redhat.com>
Cc: Peter Krempa <pkrempa@redhat.com>,
	Juan Quintela <quintela@redhat.com>,
	qemu-devel@nongnu.org, Markus Armbruster <armbru@redhat.com>,
	Paolo Bonzini <pbonzini@redhat.com>, Den Lunev <den@openvz.org>,
	Andrey Gruzdev <andrey.gruzdev@virtuozzo.com>
Subject: Re: [PATCH v4 0/6] UFFD write-tracking migration/snapshots
Date: Tue, 1 Dec 2020 20:01:37 +0000	[thread overview]
Message-ID: <20201201200137.GQ4338@work-vm> (raw)
In-Reply-To: <20201201192247.GF3277@xz-x1>

* Peter Xu (peterx@redhat.com) wrote:
> On Tue, Dec 01, 2020 at 06:40:55PM +0000, Dr. David Alan Gilbert wrote:
> > > Yep, seems that current userfaultfd supports hugetlbfs and shared memory for
> > > missing pages but not for wr-protected..
> > 
> > For hugepages, you'd need kernel support - but also you'd want to make
> > sure you write the whole hugepage at once.
> 
> Or we can do similar things by splitting the huge pages just like when we
> migrate.
> 
> I should have overlooked these facts when I replied previusly - we do need the
> same logic, but also special care on these special memory types.
> 
> > 
> > For shared, there's a harder problem to ask; what happens if RAM is
> > written by the other process - for postcopy, we get the other process
> > to send us a userfaultfd that they have registered with their VM.
> 
> Good point... so we should need similar things too.
> 
> Looks like we'd better explicitly disable shmem/hugetlbfs for now from qemu
> background snapshots before we have prepared these utilities, just in case it
> got run on some "future" kernels and accidentally got enabled, so the snapshot
> files could be corrupted ones.
> 
> Is shmem used a lot in libvirt, or is it even a default configuration?

No, but it's used with vhost-user applications; like dpdk.

Dave

> -- 
> Peter Xu
> 
-- 
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK



  reply	other threads:[~2020-12-01 20:03 UTC|newest]

Thread overview: 45+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-11-26 15:17 [PATCH v4 0/6] UFFD write-tracking migration/snapshots Andrey Gruzdev via
2020-11-26 15:17 ` [PATCH v4 1/6] introduce 'background-snapshot' migration capability Andrey Gruzdev via
2020-11-27 19:55   ` Peter Xu
2020-11-28 16:35     ` Andrey Gruzdev
2020-11-26 15:17 ` [PATCH v4 2/6] introduce UFFD-WP low-level interface helpers Andrey Gruzdev via
2020-11-27 21:04   ` Peter Xu
2020-11-29 20:12     ` Andrey Gruzdev
2020-11-30 15:34       ` Peter Xu
2020-11-30 18:41         ` Andrey Gruzdev
2020-12-01 12:24   ` Dr. David Alan Gilbert
2020-12-01 19:32     ` Andrey Gruzdev
2020-11-26 15:17 ` [PATCH v4 3/6] support UFFD write fault processing in ram_save_iterate() Andrey Gruzdev via
2020-11-27 21:49   ` Peter Xu
2020-11-29 21:14     ` Andrey Gruzdev
2020-11-30 16:32       ` Peter Xu
2020-11-30 19:27         ` Andrey Gruzdev
2020-11-26 15:17 ` [PATCH v4 4/6] implementation of background snapshot thread Andrey Gruzdev via
2020-11-26 15:17 ` [PATCH v4 5/6] the rest of write tracking migration code Andrey Gruzdev via
2020-11-27 22:26   ` Peter Xu
2020-11-30  8:09     ` Andrey Gruzdev
2020-11-26 15:17 ` [PATCH v4 6/6] introduce simple linear scan rate limiting mechanism Andrey Gruzdev via
2020-11-27 22:28   ` Peter Xu
2020-11-30  8:11     ` Andrey Gruzdev
2020-11-30 16:40       ` Peter Xu
2020-11-30 19:30         ` Andrey Gruzdev
2020-11-26 15:47 ` [PATCH v4 0/6] UFFD write-tracking migration/snapshots Peter Krempa
2020-11-27  8:21   ` Andrey Gruzdev
2020-11-27  9:49     ` Peter Krempa
2020-11-27 10:00       ` Andrey Gruzdev
2020-11-27 15:45         ` Peter Xu
2020-11-27 17:19           ` Andrey Gruzdev
2020-11-27 22:04 ` Peter Xu
2020-11-30  8:07   ` Andrey Gruzdev
2020-12-01  7:08 ` Peter Krempa
2020-12-01  8:42   ` Andrey Gruzdev
2020-12-01 10:53     ` Peter Krempa
2020-12-01 11:24       ` Andrey Gruzdev
2020-12-01 18:40         ` Dr. David Alan Gilbert
2020-12-01 19:22           ` Peter Xu
2020-12-01 20:01             ` Dr. David Alan Gilbert [this message]
2020-12-01 20:29               ` Andrey Gruzdev
2020-12-01 20:11           ` Andrey Gruzdev
2020-12-01 18:54         ` Peter Xu
2020-12-01 20:00           ` Dr. David Alan Gilbert
2020-12-01 20:26           ` Andrey Gruzdev

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