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From: Peter Xu <peterx@redhat.com>
To: "Dr. David Alan Gilbert" <dgilbert@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 14:22:47 -0500	[thread overview]
Message-ID: <20201201192247.GF3277@xz-x1> (raw)
In-Reply-To: <20201201184055.GM4338@work-vm>

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?

-- 
Peter Xu



  reply	other threads:[~2020-12-01 19:24 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 [this message]
2020-12-01 20:01             ` Dr. David Alan Gilbert
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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