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Re: [PATCH v2 0/6] migration/ram: Optimize for virtio-mem via RamDiscard
From: |
Peter Xu |
Subject: |
Re: [PATCH v2 0/6] migration/ram: Optimize for virtio-mem via RamDiscardManager |
Date: |
Fri, 23 Jul 2021 12:12:46 -0400 |
On Thu, Jul 22, 2021 at 01:43:41PM +0200, David Hildenbrand wrote:
> > > a) In precopy code, always clearing all dirty bits from the bitmap that
> > > correspond to discarded range, whenever we update the dirty bitmap.
> > > This
> > > results in logically unplugged memory to never get migrated.
> >
> > Have you seen cases where discarded areas are being marked as dirty?
> > That suggests something somewhere is writing to them and shouldn't be.
>
> I have due to sub-optimal clear_bmap handling to be sorted out by
>
> 20210722083055.23352-1-wei.w.wang@intel.com">https://lkml.kernel.org/r/20210722083055.23352-1-wei.w.wang@intel.com
>
> Whereby the issue is rather that initially dirty bits don't get cleared in
> lower layers and keep popping up as dirty.
>
> The issue with postcopy recovery code setting discarded ranges dirty in
> the dirty bitmap, I did not try reproducing. But from looking at the
> code, it's pretty clear that it would happen.
>
> Apart from that, nothing should dirty that memory. Of course,
> malicious guests could trigger it for now, in which case we wouldn't catch it
> and migrate such pages with postcopy, because the final bitmap sync in
> ram_postcopy_send_discard_bitmap() is performed without calling notifiers
> right now.
I have the same concern with Dave: does it mean that we don't need to touch at
least ramblock_sync_dirty_bitmap in patch 3?
Doing that for bitmap init and postcopy recovery looks right.
One other trivial comment is instead of touching up ram_dirty_bitmap_reload(),
IMHO it's simpler to set all 1's to disgarded memories on dst receivedmap;
imagine multiple postcopy recovery happened, then with that we walk the disgard
memory list only once for each migration. Not a big deal, though.
--
Peter Xu
- Re: [PATCH v2 5/6] migration/postcopy: Handle RAMBlocks with a RamDiscardManager on the destination, (continued)
- Re: [PATCH v2 5/6] migration/postcopy: Handle RAMBlocks with a RamDiscardManager on the destination, David Hildenbrand, 2021/07/23
- Re: [PATCH v2 5/6] migration/postcopy: Handle RAMBlocks with a RamDiscardManager on the destination, Peter Xu, 2021/07/23
- Re: [PATCH v2 5/6] migration/postcopy: Handle RAMBlocks with a RamDiscardManager on the destination, David Hildenbrand, 2021/07/23
- Re: [PATCH v2 5/6] migration/postcopy: Handle RAMBlocks with a RamDiscardManager on the destination, Peter Xu, 2021/07/23
- Re: [PATCH v2 5/6] migration/postcopy: Handle RAMBlocks with a RamDiscardManager on the destination, David Hildenbrand, 2021/07/29
- Re: [PATCH v2 5/6] migration/postcopy: Handle RAMBlocks with a RamDiscardManager on the destination, Peter Xu, 2021/07/29
[PATCH v2 6/6] migration/ram: Handle RAMBlocks with a RamDiscardManager on background snapshots, David Hildenbrand, 2021/07/21
Re: [PATCH v2 0/6] migration/ram: Optimize for virtio-mem via RamDiscardManager, Dr. David Alan Gilbert, 2021/07/22
- Re: [PATCH v2 0/6] migration/ram: Optimize for virtio-mem via RamDiscardManager, David Hildenbrand, 2021/07/22
- Re: [PATCH v2 0/6] migration/ram: Optimize for virtio-mem via RamDiscardManager,
Peter Xu <=
- Re: [PATCH v2 0/6] migration/ram: Optimize for virtio-mem via RamDiscardManager, David Hildenbrand, 2021/07/23
- Re: [PATCH v2 0/6] migration/ram: Optimize for virtio-mem via RamDiscardManager, Peter Xu, 2021/07/23
- Re: [PATCH v2 0/6] migration/ram: Optimize for virtio-mem via RamDiscardManager, David Hildenbrand, 2021/07/27
- Re: [PATCH v2 0/6] migration/ram: Optimize for virtio-mem via RamDiscardManager, Peter Xu, 2021/07/27
- Re: [PATCH v2 0/6] migration/ram: Optimize for virtio-mem via RamDiscardManager, David Hildenbrand, 2021/07/28
- Re: [PATCH v2 0/6] migration/ram: Optimize for virtio-mem via RamDiscardManager, Peter Xu, 2021/07/28
- Re: [PATCH v2 0/6] migration/ram: Optimize for virtio-mem via RamDiscardManager, David Hildenbrand, 2021/07/28
- Re: [PATCH v2 0/6] migration/ram: Optimize for virtio-mem via RamDiscardManager, Peter Xu, 2021/07/28
- Re: [PATCH v2 0/6] migration/ram: Optimize for virtio-mem via RamDiscardManager, David Hildenbrand, 2021/07/29
- Re: [PATCH v2 0/6] migration/ram: Optimize for virtio-mem via RamDiscardManager, Peter Xu, 2021/07/29