RE: [PATCH] migration: Move bitmap_mutex out of migration_bitmap_clear_dirty()

[Wang, Wei W]

On Thursday, July 1, 2021 10:22 PM, David Hildenbrand wrote:
> On 01.07.21 14:51, Peter Xu wrote:
> Spoiler alert: the introduction of clean bitmaps partially broke free page 
> hinting
> already (as clearing happens deferred -- and might never happen if we don't
> migrate *any* page within a clean bitmap chunk, so pages actually remain
> dirty ...). "broke" here means that pages still get migrated even though they
> were reported by the guest. We'd actually not want to use clean bmaps with 
> free
> page hinting ... long story short, free page hinting is a very fragile beast 
> already
> and some of the hints are basically ignored and pure overhead ...

Not really. Both clear_bmap and free page hint are to "clear" the bitmap.
No matter who comes first to clear it, it won’t cause more (unexpected) pages 
to be sent.

Best,
Wei