Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> writes:
> On Fri, 24 Feb 2023 22:11:42 +0800 Huang Ying <ying.huang@xxxxxxxxx> wrote:
>
>> Two deadlock bugs were reported for the migrate_pages() batching
>> series.
>
> "migrate_pages(): batch TLB flushing"
Yes. Should have written as that.
>> Thanks Hugh and Pengfei. Analysis shows that if we have
>> locked some other folios except the one we are migrating, it's not
>> safe in general to wait synchronously, for example, to wait the
>> writeback to complete or wait to lock the buffer head.
>>
>> So 1/3 fixes the deadlock in a simple way, where the batching support
>> for the synchronous migration is disabled. The change is
>> straightforward and easy to be understood. While 3/3 re-introduce the
>> batching for synchronous migration via trying to migrate
>> asynchronously in batch optimistically, then fall back to migrate
>> synchronously one by one for fail-to-migrate folios. Test shows that
>> this can restore the TLB flushing batching performance for synchronous
>> migration effectively.
>
> If anyone backports the "migrate_pages(): batch TLB flushing" series
> into their kernels, they will want to know about such fixes. So we can
> help them by providing suitable Link: tags.
>
> Such a Link: may also be helpful to people who are performing git
> bisection searches for some issue but who keep stumbling over the
> issues which this series addresses.
>
> Being lazy, I slapped
>
> Fixes: 6f7d760e86fa ("migrate_pages: move THP/hugetlb migration support check to simplify code")
>
> on all three, as this was the final patch in that series. Inaccurate,
> but it means that these fixes will land in a suitable place if anyone
> needs them.
Sorry. I should have added the "Fixes:" tag. I will be more careful
in the future. And, I will add proper "Link:" tag too.
Best Regards,
Huang, Ying
