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

[Wang, Wei W]

On Thursday, July 8, 2021 12:55 AM, Peter Xu wrote:
> On Wed, Jul 07, 2021 at 08:34:50AM +0000, Wang, Wei W wrote:
> > On Wednesday, July 7, 2021 1:47 AM, Peter Xu wrote:
> > > On Sat, Jul 03, 2021 at 02:53:27AM +0000, Wang, Wei W wrote:
> > > > +       do {
> > > > +            page_to_clear = start + (i++ <<
> > > > + block->clear_bmap_shift);
> > >
> > > Why "i" needs to be shifted?
> >
> > Just move to the next clear chunk, no?
> > For example, (1 << 18) pages chunk (i.e. 1GB).
> 
> But migration_clear_memory_region_dirty_bitmap() has done the shifting?
> 

Please see this example: start=0, npages = 2 * (1 <<18), i.e. we have 2 chunks 
of pages to clear, and start from 0.
First chunk: from 0 to (1 <<18);
Second chunk: from (1 << 18) to 2*(1<<18).

To clear the second chunk, we need to pass (start + "1 << 18") to 
migration_clear_memory_region_dirty_bitmap(),
and clear_bmap_test_and_clear() there will do ">>18" to transform it into the 
id of clear_bitmap, which is 1.

Best,
Wei