Re: [PATCH 5/8] migrate_pages: batch _unmap and _move

["Huang, Ying" <ying.huang@intel.com>]

Zi Yan <ziy@nvidia.com> writes:

> On 26 Dec 2022, at 19:28, Huang Ying wrote:
>
>> In this patch the _unmap and _move stage of the folio migration is
>> batched.  That for, previously, it is,
>>
>>   for each folio
>>     _unmap()
>>     _move()
>>
>> Now, it is,
>>
>>   for each folio
>>     _unmap()
>>   for each folio
>>     _move()
>
> Also worth adding some notes here, we need extra code to undo the _unmap()
> if _move() fails. Andrew has asked for comments on *_undo_src/dst(),
> but I think it would be better to provide a high level new workflow,
> in the form of pseudo code, in git log and the comment for migrate_pages().
> The extra cleanup code for a failed _move() with a previously successful
> _unmap() might not be obvious to everyone.

Here, I removed the detailed error processing to make it easier to
understand the basic flow changing.  So, I would rather to keep the
pseudo code here as simple as possible and keep the detailed flow in the
diff below.

Best Regards,
Huang, Ying

>>
>> Based on this, we can batch the TLB flushing and use some hardware
>> accelerator to copy folios between batched _unmap and batched _move
>> stages.
>>

[snip]