Re: [PATCH] mm/vmstat: Add events for PMD based THP migration without split

[John Hubbard]

On 2020-06-01 21:20, Anshuman Khandual wrote:
...
> > also important: maybe this patch should also be tracking other causes
> > of THP PMD migration failure, in order to get a truer accounting of the
> > situation.

I hope one of the experts here can weigh in on that...

> Is there any other failure reasons which are only specific to THP migration.
> Else, adding stats about generic migration failure reasons will just blur
> the overall understanding about THP migration successes and failure cases
> that results in splitting.

Thinking about that: we do have PGMIGRATE_SUCCESS and PGMIGRATE_FAIL, so I
suppose comparing those numbers with the new THP_PMD_MIGRATION_SUCCESS and
THP_PMD_MIGRATION_FAILURE events should cover it.

However, the fact that this is under discussion hints at the need for a
bit of documentation help. What do you think about adding some notes about
all of this to, say, Documentation/vm/page_migration.rst ?

thanks,
--
John Hubbard
NVIDIA